Can Naiades: 15 steps towards a comfortable, healthy, resilient, and efficient home

Can Naiades is a single-family, 4 bedroom, 2 storey Passivhaus Plus home, located in Sant Julia d’Alfou, in the province of Barcelona, Catalonia, Spain. Designed by Daniel Tigges from Tigges Architekt, with Oftecnics as Quantity Surveyor/Site Supervisor, the house is built by House Habitat, with Fontalgar Instalaciones installing electrical and mechanical services, and Praxis Resilient Buildings providing Passivhaus design, HVAC system design and Blower Door testing. The house is being certified to Passivhaus standard by Micheel Wassouf of Energiehaus Arquitectos.

1. Bioclimatic design

The house is built on a site that is sloped from east to west, with large stone retaining walls creating a platform where the house can sit with the longest façades aligned south / north. To maximise solar gain and daylighting, the windows on the southern façade make up 72% of the total window area, meaning that around 79% of the home’s heating requirements will be provided by the sun (14% will be provided by internal heat gains and the remaining 7% by the active heating system). Southern glazing is shaded in the summer by the balcony on the intermediate floor and a roof overhang, with external venetian blinds on all windows. The house has a relatively compact design with a heat loss form factor of 462 ÷ 128 = 3.6 (total envelope area ÷ treated floor area).

2. Geobiological survey

Early in the design process, a geobiological survey of the site was done by Architect Sonia Hernandez from the Arquitectura Sana, to measure electromagnetic radiation on the plot and identify possible sources of contamination. Low frequency electric and magnetic fields, high frequency electromagnetic fields, geological alterations, gamma and neutronic radiation, and terrestrial magnetic fields were measured. The results of the survey showed some terrestrial magnetic fields where beds were located in two of the first-floor bedrooms. The layout of the upstairs bedrooms was therefore modified to avoid potential health problems associated with long-term exposure. Another recommendation from the survey was to ensure that cabling in the bedrooms was shielded to avoid electromagnetic radiation while sleeping. As far as possible, low emission materials have been used to reduce indoor contaminants.

3. Timber structure

The house is built with a lightweight timber structure assembled off-site by EGOIN, in the Basque country (northern Spain), using local radiata pine timber. The wall modules consist of 140mm timber studs, filled with recycled glass wool insulation and enclosed internally with a 12mm particle board and externally with a 12mm OSB 3 board.

The roof modules consist of 200mm joists, filled with recycled glass wool insulation, enclosed internally with a dynamic vapour control membrane and externally with an 18mm OSB 3 board.

The intermediate floor and roof modules all came factory fitted with a SIGA Wetguard waterproof membrane, to protect them from rain during on-site assembly. Due the double height design in the sitting room area, a part of the structure on the northern façade consists of 150mm Cross Laminated Timber (CLT) panels, together with a steel frame structure.

The wall and roof modules were delivered to site and the house was erected and waterproofed in only 8 working days, bringing with it all the advantages of off-site prefabrication: rapid onsite assembly, greater precision and build quality, less waste, and optimization of materials.

4. Earthing system

A good earthing system is particularly important in timber houses, to avoid electromagnetic radiation from cables and appliances that can affect occupants’ health. To this end, four 3-meter cooper earth rods were installed, connected to an earth cable, in turn connected to the reinforced steel structure of the concrete floor slab. The reinforced steel structure itself was also welded at specific points to ensure a good electrical connection across the slab. The connections between copper and steel were sealed with a special paste to prevent galvanic corrosion and ensure a good earth connection for the working life of the building. A resistance to ground of ≤ 6 Ohms is recommended: once the earthing system was complete, the measured result was 2.15 Ω. Fantastic!

5. Thermal insulation

The walls and roof of Can Naiades are insulated with Knauf Insulation recycled glass wool insulation, chosen for fire resistance, good thermal performance and because they incorporate a bio-based E-Technology binder, free from added phenols and formaldehydes, protecting both the workers on site and future occupants from harmful emissions. The walls are insulated within the timber structure with 140mm, together with 60mm externally, and a further 50mm in the internal service void. The roof has 200mm of insulation between the timber structure, and a further 150mm on top. Between 100mm and 200mm of XPS insulation has been installed under the concrete floor slab. Supplied by Pafile, small amounts of aerogel- about the most insulating material there is for use in buildings- has been used to insulate specific sections of steel I-beams that were needed to reinforce the structure. Steel is a good heat conductor, so the aerogel blankets reduce thermal bridging, heat loss and cold spots where the steel penetrates the thermal envelope. 

6. Radon gas barrier

The floor slab is painted with a Soudatight liquid membrane made by Soudal, to form a radon gas barrier. This prevents the entrance of radon gas, which is naturally occurring, carcinogenic, invisible, and odourless, emitted from granitic rocks, and which can seep into building through floor slabs and walls to ground (for more information, see this article on radon gas).

7. Openings

The windows consist of triple glazed, argon-filled, low emissivity glazing and Passivhaus certified Smartwin timber-aluminium window frames made by Ventanas Gardea. Window thermal bridges are reduced to a minimum by insulating most of the fixed part of the frames. For the sills of the sliding and french windows, the frames are installed on an Isotop Winframer high density EPS board made by Iso Chemie, to reduce thermal bridging and cold spots. A FAKRO DEC quadruple-glazed roof light provides daylighting to the stairwell to the north. A Passivhaus certified airtight and insulated Petwalk cat flap will let the cat in and out with minimal heat loss.

8. Airtightness and vapour control

SIGA airtight tapes have been used for all the airtight sealing. A SIGA Majrex 200 dynamic membrane provides the air barrier and vapour control layer in the roof. The membrane has a variable vapour diffusion resistance, which means in winter it acts as a vapour barrier, and in summer, it lets vapour pass through. This protects the roof modules from the exfiltration of warm and humid air in the winter (important for avoiding interstitial condensation damage in flat non-ventilated timber roofs) and allows back drying in the summer (in case any humidity has accumulated during the winter, or due a water leak- whether during construction or in the future). A FINSA Superpan VapourStop particle board provides the air barrier and vapour control layer in the external walls. The house will undergo a whole-building Blower Door airtightness test, to meet the stringent Passivhaus requirement of n50 ≤ 0.6 ach. This means the equivalent total surface area of all the air leaks in the house will constitute a hole about 10cm x 10cm.

9. Ventilation

Clearly you can’t build an airtight, draught-free home without making sure the space is adequately ventilated, otherwise air quality would be terrible and there’d be way too much humidity in the indoor air. Added to this, every day, while we eat an average of 1kg of food and drink around 2 litres of water, we breath around 8000 litres of air. So reliable ventilation and good air quality are really important! In Can Naiades we’re using a Zehnder balanced whole-house mechanical ventilation system with heat recovery, that recovers around 90% of the heat from outgoing stale air and uses it to preheat incoming air. In the summer the heat recovery process is reversed, whereby incoming air is cooled by the relatively cooler outgoing stale air. If the outdoor air temperature is lower than the indoor temperature, an automatic bypass opens so that relatively cooler outdoor air is let in directly, providing “free cooling”.  In the entire process, the heat recovery unit consumes about the same amount of electricity as 2 low-energy light bulbs. The system blows pre-heated (or pre-cooled in the summer) fresh air into the bedrooms, sitting room and office, and extracts stale air from the kitchen and bathrooms, working 24 h/d, 365 days/year, silently and efficiently. The heat recovery unit includes a F7 filter on the incoming outdoor, removing pollutants in the outdoor air, which will mainly come from wood fires in the winter.

10. Keeping cool in the summer

Heat waves have been a feature of recent years, and are set to increase over the coming decades, so a series of design strategies have been implemented that will help keep the house cool, using very little energy. A balcony between the ground and first floor, together with the roof overhang, shade the southern glazing in the summer. All windows have Griesser Solomatic external venetian blinds, with slats that can be adjusted to let in natural light but block direct sunlight. The FAKRO roof light has an external awning to block solar gain, together with a motorised opening mechanism, which means it can be opened when it’s hot inside and cooler outside, drawing cool air in through the ground floor and 1^st floor bedrooms and out through the roof light. The height difference provides higher air flow rates through what’s called the “stack” effect. The office and bedroom windows all have mosquito netting so then can be left tilted open at night, without bugs coming in. As in vernacular Mediterranean architecture, the house is rendered white on most of the façade, which means it reflects more sun in the summer and keeps cooler. 3 deciduous black poplar trees to the south and west of the house have been kept in place, to provide additional shading in the summer.

11. Heating & cooling

Comfort heating and cooling is provided by a Zehnder ComfoClime Q autonomous heat pump heating/cooling coil on the ventilation system. In heating mode, the heat pump extracts heat from the extract air and passes it to the supply air, heating it to up to 49ºC. In cooling mode, the unit extracts heat from the supply air and passes it to the extract air, cooling it down to 12ºC. This way, during most of the year, the heating and cooling needs of the home will be covered by the ventilation supply air, providing up to 3.8 kW of heating power and 1.7 kW of cooling power at a flow rate of 400 m3/h.

For peak cooling loads, a Panasonic Aquarea Ecoflex heat pump with a 7kW indoor ducted split unit, recirculates indoor air and removes heat from the building. Instead of dumping that heat to the outdoor air (as traditional air conditioners do) the Ecoflex recovers heat and transfers it the Domestic Hot Water (DHW) tank, thus reducing summer hot water energy consumption.

12. Domestic Hot Water (DHW)

The Panasonic Aquarea Ecoflex heat pump produces hot water for washing and showering, extracting heat from the outdoor air and transferring it to water in the DHW tank, moving- on average- 3.4 units of heat for every 1 unit of electricity (i.e. extremely efficient). As explained above, the heat pump has a heat recovery function when operating in cooling mode, where heat removed from the home is used to pre-heat hot water in the tank.  This increases the heat pump’s performance by around 52%, i.e. it moves 5.1 units of heat for every 1 unit of electricity. Alongside this, each shower is equipped with a Zypho drain water heat recovery system supplied by Aliaxis, using the heat from wastewater to preheat incoming cold water, reducing DHW energy consumption by between 30% and 50%. The hot water tank and the bathrooms have been located close enough to each other, to avoid the need for a DHW recirculation loop, avoiding the associated heat losses (which then become heat gains in the summer…).

13. Solar photovoltaic generation

Can Naiades will have 18 roof mounted solar PV panels (6,7 kWp in total) installed by Prot Energia, which’ll generate around 7000 kWh/a. This means the home, on an annual basis, will generate around 25% more electricity that it consumes.

14. Water saving

Saving energy is good but so is saving water. During the design phase there was a major drought in Catalonia, so the owners were clear that saving water was also a priority, given that droughts and heat waves are only set to increase over the coming decades. To this end, a series of water saving solutions have been included in the home, to radically reduce water consumption. First up, an Intewa grey water treatment system supplied by Ecospai takes wastewater from showers and sinks, cleans it, and pumps it back to toilet cisterns and to the washing machine. Secondly, low-flow shower heads and taps reduce water consumption. In the ground floor bathroom, there is a dry urinal, which precludes the need to use a flush toilet and saves around 4 litres of water that goes down the drain on each flush. Lastly, a rain catchment system collects water for garden watering. There will be no swimming pool, and the garden will include local Mediterranean plant species that don’t need much water.

15. Monitoring & control

The home will be monitored to track energy and water consumption using the Loxone control system, supplied by HEBHAUS, along with MICA indoor air quality sensors supplied by INBIOT and radon gas sensors supplied by Bequerel. Additionally, the Loxone system will be used to control blinds, outdoor lighting, a video intercom, a car charger and the heating, cooling and ventilation system.

The owners would like to thank all of the following people and companies for their support with the project:

Tigges Architekt

Aliaxis

Arquitectura Sana

Bequerel

Ecospai

EGOIN

Energiehaus Arquitectos

Fontalgar Instalaciones

FAKRO

Ventanas Gardea

Griesser

HEBHAUS

House Habitat

INBIOT

Iso Chemie

Knauf Insulation

Loxone

Pafile

Panasonic

Petwalk

Prot Energia

SIGA

Soudal

Zehnder

Delivering large Passivhaus buildings: Site Supervisor & Construction Verifier training

The article presents the experiences and lessons learned from our Passivhaus Site Supervisor and Construction Verifier training courses.

The courses provide architects and engineers with the tools they need for delivering large and complex Passivhaus buildings, achieving certification and reigning in cost overruns. 

Large and complex Passivhaus buildings: reducing risk and reigning in cost overruns through practical online training

“Your course has saved me at least 20,000 € in construction costs”

This was the feedback we got from the developer of a small multi-residential building we consulted on, following the online Site Supervisor course we gave to his team. The building was developed, designed, and built by a team with no prior experience in Passivhaus and has now achieved Passivhaus Classic certification.

Lack of experience increases the risk of cost overruns during the construction phase- particularly in relation to the execution of the airtight layer and achieving the required result in the final Blower Door test. Our experience with Site Supervisor and Construction Verifier training is that the courses provide architects and engineers with the tools they need for successful site supervision and navigation of the certification process, and deliver important on-site savings for developers and contractors. 

Another client, FIATC Residencias, who are developing 7 elderly people’s residencies that are all aiming for Passivhaus certification, have made our Site Supervisor and Construction Verifier course obligatory for the contractors, installers, and design teams on each project, with 3 courses held to date. In the course satisfaction survey, one student reported:

“I particularly want to highlight how useful it was to get all of us who’ll be working on-site together on the course, including both civil works and mechanical and electrical contractors”. 

Bridging the gap between Passivhaus design and Passivhaus construction: online Site Supervisor & Construction Verifier training

According to the PHI database, as of 2023, there were over 700 certified Passivhaus Designers in Spain and over 1300 Passivhaus Tradesperson, compared with 195 and 25 respectively in Germany. This suggests that Passivhaus design and tradesperson training has got off to a good start in the construction sector.

However, despite extensive Passivhaus Designer and Tradesperson training, there is a clear knowledge gap when it comes to the construction and certification of large and complex Passivhaus buildings. This is where the official Passivhaus Site Supervisor and Construction Verifier courses come in: they are especially designed to fill that gap, helping contractors, installers, site managers and tradespeople in the successful execution of large and complex Passivhaus buildings, on time, on budget, and compliant with Passivhaus certification. 

While the courses can be taken by any construction professional, those with Tradesperson and Designer qualifications can acquire the Site Supervisor or Construction Verifier add-ons, if they take the course and pass the exam (shown in Figure 2). At the time of writing, we have held two exams, leading to the first qualified Site Supervisors and Construction Verifiers in Spain. 

The format used for the courses and for the exam is 100 % online, making an easier fit with on-site work and other commitments. Exam preparation includes an intensive on-line class, with review of the course content and question and answer time. The Site Supervisor exam must be completed in under 45 minutes, and the Construction Verifier exam in under 2 hours, both done online. 

Praxis uses proprietary course material, based on abundant practical examples of on-site situations using photographs and videos. During each course, there are always two trainers, one giving the content and another attending the live chat, launching surveys, and posting references to documentation on the online campus, where 77 technical articles, guides and how-to documents are available for reading and download. A forum in the online campus provides a space for participants to ask questions, exchange ideas, and generate debate. The participants on our courses are often from very different countries and technical backgrounds, providing a rich and diverse learning environment.The Site Supervisor course consists of 4 modules, while the Construction Verifier course includes 8 modules, with the courses held concurrently.

Summary of the modules for each course and their content

Every online session includes a guest speaker, presenting a specific technical issue relating to the module in question. Both during and at the end of each session, multiple choice questions are presented online to the students, to consolidate learning and generate debate and reflection. Each online session is also recorded and made available for watching offline, with attendees commenting that they found them to be a useful resource for reviewing and taking notes after the online classes. Additionally, and to provide networking opportunities, we offer site visits for all students, so they can see a Passivhaus building under construction in the month or two following the course.

Feedback

Each course includes on online student satisfaction survey. Some of the answers provide by students are shown below:

Filling the gap for a successful execution of large and complex Passivhaus buildings

Official Passivhaus Site Supervisor and Construction Verifier courses come in: they are especially designed to fill that gap, helping contractors, installers, site managers and tradespeople in the successful execution of large and complex Passivhaus buildings, on time, on budget, and compliant with Passivhaus certification. 

The growth in Passivhaus construction in Spain in recent years has been significant: in 2021, Spain was ranked 2^nd in the world after China, with the most square meters of floor space certified to the Passivhaus standard. Increasingly, larger, and more complex Passivhaus buildings are being designed or retrofitted, tendered and built by large “mainstream” contractors and installers who often have little experience in executing Passivhaus buildings. The Site Supervisor and Construction Verifier courses provide contractors, installers, site managers and tradespeople with the knowledge they need for the successful execution of large and complex Passivhaus buildings.

Dealing with heat waves: can I use the PHPP to size cooling equipment?

The issue of correctly sizing cooling equipment is key if we are to maintain thermal comfort, at low power

The article looks at using the PHPP for sizing cooling equipment and compares results with multi-zone calculations using dynamic simulation

Given ever more frequent heat waves and the increasing need for active cooling in Passivhaus residential buildings, the issue of correctly sizing cooling equipment is key if we are to maintain thermal comfort, at low power. Over-sizing of cooling plant adds unnecessary cost and energy consumption, increasing stress on power grids as they try and meet peak loads, especially under heat wave conditions. Under-sizing cooling plant will lead to comfort problems, failed expectations and a performance gap that Passivhaus buildings have been consistently shown to fill. Once the work has gone into creating a working PHPP model, can we safely use the tool to size cooling kit?

The article looks at using the PHPP for sizing cooling equipment and compares results with multi-zone calculations using dynamic simulation, based on a simple worked example of a completed and certified Passivhaus residential building in climate zone 5-Warm. The research was prompted by the (painful) lessons learned some years ago, when using the PHPP to size cooling equipment for a single-family low-energy home with Passivhaus components, without adequate modification of boundary conditions. The home had active cooling but suffered from overheating problems and complaints from occupants.

How does PHPP calculate cooling loads?

PHPP calculates sensible and latent cooling loads as the maximum daily average cooling power required to maintain the operative temperature set point, providing an average cooling load across the whole building, based on maximum daily average outdoor air temperature, dew point, sky temperature and solar radiation. Occupancy gains are typically based on a default setting (e.g., for TFA = 150m², occupancy ratio = 51 m²/p, occupancy = 2.9 people. 

How does a dynamic simulation tool calculate cooling loads?

Dynamic simulation tools allow for a multi-zone calculation based on hourly climate data, occupancy activity, and equipment operation, providing a time-dependent, high-resolution calculation of cooling loads. Typically, solar gains are calculated on an hourly time-step, and occupancy gains are computed dynamically, such that latent gains increase, and sensible gains decrease, as indoor operative temperature increases (people begin to sweat more as indoor temperature increases…). Is this level of accuracy really necessary, or can we use the PHPP to size cooling plant?

Which kind of tool should I use to size cooling equipment?

Finding the right answer to the question involves asking some the following questions: what building typology are we dealing with? What are the local short-term climate conditions, over 24 hours, during the hottest days? What is the occupancy density of the building, what are the internal heat gains and solar gains, and at what time in the day do they occur? Logically, a single zone, quasi-steady state calculation method such as the one found in PHPP, will be pushed to its limits for larger buildings and/or those with short-term peak gains derived from solar radiation, occupancy or equipment use, particularly if they vary greatly from one zone to the other.

Worked example: PHPP vs. dynamic simulation cooling load calculation for single-family home

Table 1 and Figure 2 shows peak cooling load results per zone, for a single-family certified Passivhaus in Mallorca, Spain, with a TFA of 170m², comparing a dynamic multi-zone calculation using DesignBuilder/EnergyPlus, with PHPP single-zone results. The PHPP climate file for the energy balancing calculations is ES0022b-Palma de Mallorca, but the climate file boundary conditions have been adjusted in the PHPP for the conditions shown in Figure 1 (derived from an hourly data set generated by Meteonorm v.7), with an outdoor air temperature of 38.1ºC and a dew point temperature of 27.2ºC (taken from the average 24-hour relative humidity of 54% @ 38.1ºC dry air temperature). The following adjustments were also made in the PHPP: the occupancy was increased to 10 people, the cooling set-point was reduced to 24ºC, and the solar factor of the glazing was increased by 5% (to eliminate the default soiling factor included in the Glazing worksheet), in agreement with the boundary conditions used in the dynamic calculation.

Figure 1: Climate conditions for cooling load calculation

Figure 2: Results of total cooling loads

The results shown in Table 1 and Figure 2 indicate a negligible 1% difference in the total average peak cooling load results at building level, between the dynamic multi-zone calculation and the PHPP results, suggesting that if the PHPP boundary conditions are modified from those used for building certification, the tool can be safely used for sizing cooling equipment for small residential buildings. This approach has been used on many projects of this type for many years with no complaints of overheating from occupants. However, if we look at peak cooling loads on a zone-to-zone basis, they vary by a + 68% (toilet) and -58% (corridor). While this has generally not been found to be a problem in practice in single-family homes, this suggests caution is required with larger buildings or for zones in smaller buildings with higher short-term peak gains (from solar radiation, occupancy or equipment use). Also, cooling distribution must be carefully planned to ensure specific zones don’t suffer from overheating and sufficient heat is removed from each zone.

Finally, the correct sizing of refrigeration equipment is important for the following reasons:

• Oversized cooling equipment leads to higher than necessary energy consumption and therefore increased energy bills.
• If cooling power is much higher than necessary, the setpoint temperature is reached earlier and the equipment shuts down (under orders from a thermostat, which only understands temperature, not humidity). This can lead to comfort problems due to excessively high indoor humidity.

Praxis at the 27th International Passive House Conference

Held in Innsbruck, the International Passivhaus Conference combines technical presentations and visits to Passivhaus buildings.

Recent developments were presented, such as the new protocol to certify apartments within multi-family residential buildings.

The International Passive House Conference is a benchmark event in the construction sector, where professionals from all over the world get together to look at the latest trends in Passivhaus and high performance buildings. Held this year in the alpine city of Innsbruck in Austria, the event combined technical presentations, visits to passivhaus buildings and an exhibition of innovative materials and components for sustainable and energy efficient construction.

Recent developments were presented, such as the new protocol to certify apartments within multi-family residential buildings. This means it won’t be necessary to carry out a step-by-step retrofit plan to obtain EnerPHit certification, and will simplify the work for Passivhaus Designers and Certifiers, while offering a solution to owners who want to retrofit and certify their apartment. Also, a new simplified version of the PHPP was presented, for the certification of single-family homes. The idea is to streamline the design and certification process for this type of property.

Praxis CEO Oliver Style gave a presentation on the Site Supervisor and Construction Verifier training courses we provide at Praxis, which have helped developers, contractors and designers minimise risk and cost overruns. He explained how the seven editions of both courses have equipped more than 80 attendees with the tools and knowledge needed to bridge the gap between design and construction for large and complex Passivhaus projects.

It was exciting to be able to meet so many professionals from such a range of countries and share ideas on how to transform architecture and create more efficient, healthy and comfortable buildings. In these two videos, Bega Clavero and Macarena Rossetti, Passivhaus Designers at Praxis, share their experience at the 27th edition of the International Passive House Conference:

Prefabricated passive houses, a cornerstone of Construction 4.0

Is it possible to build a prefabricated Passivhaus building? Of course it is!

Prefabrication or industrialised construction is emerging as one of the cornerstones of what is known as Construction 4.0

Spain was the country with the second most Passivhaus certified square metres in the world

Prefabrication or industrialised construction is emerging as one of the cornerstones of what is known as Construction 4.0. According to the McKinsey Global Institute, the objective of this 4th Industrial Revolution is to ditch obsolete and traditional construction methods and improve productivity by more than 50%, through- among other things- the optimization of resources based on prefabrication, zero waste and circularity.

Alongside this, we have the growing trend of passive houses, or homes certified to the Passivhaus standard, a voluntary certification seal that prioritises maximum comfort and indoor air quality for users, with almost zero energy consumption. It is characterised by close attention to detail in the design phase and rigorous on site control to guarantee a high construction quality, and is based on 8 principles:

• Bioclimatic design
• Thermal insulation
• Air tightness
• Reduction of thermal bridges
• Mechanical ventilation with heat recovery
• High performance doors and windows
• Shading devices
• Efficient mechanical & electrical systems

The increase in the number of buildings with Passivhaus certification during the last 10 years is notable, reaching more than 3,86 million square metres of certified floor area in 2024. In 2020, Spain was the country with the second most Passivhaus certified square metres in the world, led by China.

The marriage of prefabrication with the Passivhaus standard seems a logical step to improve construction quality, reduce execution times and increase productivity. Let’s have a look at some of these together.

Prefabrication: What is it and how is it applied to construction?

Prefabrication or industrialization is the mass production, off site, of the construction elements of a building, transferring work that was previously carried out on site to a workshop or factory. It generally includes structural elements and thermal insulation, assembled in a series of modules such as slabs, façade walls, partitions or roofs. These modules are transported to the building site and assembled, like pieces of a puzzle to form the building.

Industrialisation opens up interesting possibilities, such as the off site installation of windows, external shading systems and some services such as electricity, waste water, ventilation or heating and cooling equipment, among others.

Advantages and drawbacks of prefabrication in passive houses

Advantages of prefabrication for passive houses:

• Rapid onsite assembly, allowing for quick weather-proofing and protection from rain and wind. This is especially important in timber construction, a material widely used in the construction of passive houses.

• Greater precision and build quality, essential for the construction of Passivhaus buildings, above all in relation to airtightness detailing and the sealing of windows and service penetrations.

• Less waste on site and a reduced environmental impact.

• Optimization of materials, through standardised production and off site assembly, reducing material waste and costs..

Some of the drawbacks:

• Detailed design of the project has to be fully complete before manufacturing and before on-site assembly begins, and allows for fewer or no modifications once on site. It should be noted that Passivhaus projects already require detailed design to be complete before beginning construction, and allow for very little on site improvisation anyway. 

• The time saved in assembling the prefabricated structure on site, is not always reflected in the total execution time of the building. Services, fittings and interior finishes continue to slow construction down.

• The size of the prefabricated elements is limited, in width and height, by the size of the transport trucks and the free height on the roads that connect the factory with the construction site.

Is it possible to build a prefabricated Passivhaus building? Of course it is! Below you can find some examples

LILU´s House: bio-based Passivhaus Plus

Passivhaus design and consultancy, for this single-family house in Abrera, Barcelona, designed by architecture firm OMB Arquitectura and built by House Habitat.

Single-family home in Sitges

Single-family home in Sitges Passivhaus design & consultancy, Blower Door Tests, M & E design, Site supervision Description Passivhaus design and consultancy, M & E engineering, and…

Learnlife Eco Hub: Passivhaus learning space

Passivhaus design & consultancy for a pop-up learning hub in Castelldefels, Barcelona, designed by the Learnlife team.

Original article written by Oliver Style and posted at caloryfrio.com

Dynamic hygrothermal simulation and full-scale validation of a structural insulated panel made from bio-based materials.

Given the environmental impact of the construction sector- responsible for 40% of the total primary energy consumption of the European Union- reducing both the embodied energy of materials at manufacturing stage and minimising operational energy consumption in buildings are urgent tasks. Timber, agricultural residues, and bio-based materials are local renewable resources that can be transformed into buildings products and components, fomenting the creation of circular economies, and reducing the environmental impact of the sector. The objective of the European ISOBIO project, that ran from 2015 to 2019, financed under the Horizon2020 program, was to address these problems through the development of new insulating materials and renders from plant fibres, agricultural residues, and bio-based binders. The article presents the results of dynamic hygrothermal simulations and full-scale validation of a structural insulated panel made from bio-based materials, for use in the construction of nearly-zero energy buildings.

ISOBIO structural insulated panel for new buildings

The prototype panel measured 1.95m x 1.95m, with a total thickness of 33.2cm in 8 layers with 9 different materials (Figure 1). The panel was rendered external with 25mm of lime and hemp plaster, applied on a rigid 50mm hemp insulation board, mechanically fixed to a 145mm red pine timber structure, filled with hemp, cotton, and flax insulation, followed by a 12mm OSB 3 timber board. An airtight and dynamic vapour control membrane was fixed to the inner face of the OSB, followed by a 45mm service void, insulated between timber battens with hemp, cotton, and flax insulation. The battens were positioned at 90º in relation to the main structural joists to reduce the thermal bridging through the timber. The inner service void was lined with a 40mm thermo-compressed straw board, plastered on the inside with 15mm of composite clay-hemp plaster, applied in 3 layers.

Test set-up

Figure 3 shows the installation of the panels in the demonstrator in Wroughton, UK. A monitoring system was installed, with a meteorological station recording external climate conditions: dry air temperature, relative humidity, solar radiation, wind speed, wind direction, rainfall, and barometric pressure. A temperature probe was installed on the outside of the panel, with a heat flow and temperature probe on the inner face, for measuring thermal transmittance in accordance with ISO 9869 [1]. In addition, temperature and relative humidity sensors were installed at 3 positions within the panel (Figure 2), to measure transient hygrothermal behaviour inside the panel and compare the results with dynamic hygrothermal simulations made with the WUFI Pro tool, following EN 15026 [2]. WUFI Pro 1D is a tool developed by the Fraunhofer Institute in Germany for assessing the hygrothermal performance of one-dimensional building envelope cross-sections, taking into account the moisture content of the materials, their transient hygrothermal performance, capillary transport and summer condensation, with hourly outdoor climate conditions. The software version used was WUFI Pro v. 6.2.1.2210

Data was measured at an interval of 5 minutes, from 24/02/2018 to 14/03/2018 in the HIVE demonstrator, UK, for a total 432 hours, or 18 days, with 5184 data points. The interior temperature was maintained at an average of 25.5 °C throughout the period, with the use of an electric convection heater.

Monitoring Results and Validation

Figure 4 shows a cross section of the modelled panel, with sensor locations. Figure 5 shows the WUFI model of the panel and corresponding sensor locations.

Figure 6 shows measured and modelled temperature and RH at position 2 (between the CAVAC rigid insulation and Biofib Trio insulation). Temperature dynamics are well reflected in the model. RH dynamics are less well reflected.

Figure 7 shows the measured and modelled temperature at position 3 (between the Biofib Trio insulation and OSB board). Temperature dynamics are well reflected in the model, with RH less so. The model nonetheless shows very close alignment with measured results.

Figure 8 shows the measured and modelled temperature and RH at position 4 (between the Intello membrane and the Biofib Trio insulation). Temperature and RH dynamics are well reflected in the model.

Figure 9 shows the measured average heat flow rate, compared with the WUFI modelled heat flow rate, showing very good agreement.

Conclusion

The results of the measured and modelled temperature and RH show good correlation, with dynamic temperature variations accurately reflected in the model. The short-term variations in relative humidity are not reflected with the same precision in the WUFI modelling results, possibly due to the assumption that the equilibrium water content in the materials is instantaneous, where in reality, there is hysteresis [3]. The hourly measured and modelled thermal transmittance data show very good correlation, with a difference of only 4% over the monitoring period.

The results indicate that bio-based materials combined in a composite SIP panel of this type can offer predictable hygrothermal performance for use in nearly-zero energy buildings.

References

• ISO 9869-1:2014 Thermal Insulation – Building elements – in-situ measurement of thermal resistance and thermal transmittance. (Aislamiento térmica – elementos constructivos – medición in-situ de la resistencia térmica y transmitancia térmica)
• UNE-EN 15026:2007, Comportamiento higrotérmico de componentes de edificios y elementos constructivos. Evaluación de la transferencia de humedad mediante simulación numérica.(Ratificada por AENOR en junio de 2010.)
• N. Reuge, F. Collet, S. Pretot, S. Moisette, M. Bart, O. Style, A. Shea, C. Lanos 2019, Hygrothermal transfers through a bio-based multilayered ISOBIO wall – Part I: Validation of a local kinetics model of sorption and simulations of the HIVE demonstrator. Laboratoire de Génie Civil et Génie Mécanique, Axe Ecomatériaux pour la construction, Université de Rennes, 3 rue du Clos Courtel, BP 90422, 35704 Rennes, France.

Healthy home: materials and indoor air quality

The U.S. EPA (Environmental Protection Agency) estimates that the air in our homes is 2 to 5 times more polluted than outdoor air. After spending so much time at home during successive COVID lockdowns, the importance of living in a healthy home has perhaps become clearer than ever before.

What kind of environmental conditions are we looking for in a healthy home? Operative or comfort temperatures of between 20 ºC – 25ºC, relative humidity between 40 % – 60%, and surface temperatures ≤ 3ºC of the indoor air temperature.  With an indoor air temperature of 20ºC and a relative humidity of 50%, interior surfaces need to be ≥ 13ºC to prevent the risk of mould growth, and ≥ 9ºC to avoid surface condensation. Exposure to mould spores can cause health issues such as eye, skin and throat irritation, nasal stuffiness, coughing and wheezing. Alongside healthy thermal conditions, good indoor air quality is key for wellbeing, solved largely by good ventilation, but also by preventing the entrance of outdoor contaminants (such as particulate matter, radon gas etc.) and by reducing the generation of indoor contaminants due to emissions from materials, furniture, and finishes.

If continuous and controlled ventilation is key, we need to get to the root of the problem: to reduce and avoid materials that emit toxic chemicals in our home. In this article Oliver Style explains what to be on the lookout for, and presents three certification systems that are useful for choosing healthy products and materials.

What does indoor air contain?

To live in a healthy environment, we need to look at the products, materials and furniture we have in our home, since we breathe the particles they emit and we are often in direct physical contact with them.

The first step is to choose paints, varnishes, timber, ceramics, textiles, and furniture with a very low emissions of Volatile Organic Compounds (VOCs). VOCs are of both natural and artificial origin. They all share the common characteristic that they are made of carbon and other elements such as hydrogen, halogens, oxygen, or sulphur. They are present in solids or liquids and are either volatile or occur in a gaseous state at room temperature, which means they move quickly around indoor spaces. Some of them modify the chemical composition of their local environment and are harmful to our health.

Formaldehyde, a colourless, volatile, and toxic gas (classified as carcinogenic by the EU), and other VOCs, are often found in paints, paint strippers, wood preservatives, wood products, binders, glues, waxes, plastics, pesticides, aerosols, synthetic carpets, cleaning products, disinfection products and degreasers. Health effects include asthma, eye, nose and throat irritation, headaches, loss of coordination, nausea, liver, kidney and central nervous system damage. VOCs can be endocrine disruptors and cause respiratory and hormonal diseases, prolonged sleep and behavioural disorders, reproductive disorders and foetal development, cancer, and multiple chemical sensitivity (MCS).

Another harmful component to pay close attention to is particulate matter (PM)- fine particles and fibres with a diameter of 10 micrometres (PM10) or less (PM2.5 and PM 1). PM2.5 particles can reach the lungs, and PM1 can reach the bloodstream. Short and long-term exposure to these particles is associated with cardiovascular and respiratory diseases, including lung cancer. These diseases become more evident when the fibres come from highly toxic materials such as asbestos.

Which are the best materials and products to use in our home?

To avoid and minimize harmful substances inside the home, it’s best to look for products that have been modified or processed as little as possible, made with low-emission paints, varnishes, and glues, formaldehyde free, and if possible, certification for low emissions. Three such certification systems are mentioned below, which classify materials and products and quantify their harmful emissions.

Linoleum or solid wood floors are recommended because they usually contain few adhesives and generally have low emissions. Anything that has been varnished or coated in a controlled factory environment (rather than on-site) will lead to lower emissions in the home. If you use laminated timber flooring, look for one that is free of formaldehyde.

Carpets are in generally not advisable, as they end up collecting all kinds of particles, and in some cases, contain volatile coal ash or polyurethane laminates. Natural fibre carpets are recommended.

Furniture and wood composite products can be a significant source of emissions because they are often made with urea-formaldehyde adhesives. Look for solid wood or plywood furniture, free of formaldehydes. 

As far as kitchen counters go, natural rock is a good option, such as quartz. Alternatively, look for Corian (a synthetic material for solid surfaces composed of acrylic resin and aluminium hydroxide).

As for thermal insulation, exposure to sprayed foam insulation containing isocyanates can cause asthma. If you use fiberglass or mineral wool insulation, make sure it’s formaldehyde free. In general, bio-based or mineral insulation are the healthiest options.

Be careful: products are sometimes sold as “ecological” due to their recycled content, but they can be harmful to your health. For example, some ceramic tiles are made with recycled glass from cathode ray tubes from old TVs, which are considered hazardous waste due to their high lead content.

Emissions & materials: certification systems

1. French certification for indoor air emissions

The label “Émissions dans l’air interieur” classifies building materials, furniture and finishing products marketed in France, being mandatory for all products sold there. The certification classifies products according to VOC emissions, from A+ to C (A+ being lowest emissions), according to the ISO 16000 standard. If a product exceeds the limits, it cannot be sold (admittedly “C” class is not very demanding…). The following emissions are evaluated:

• Formaldehyde
• Acetaldehydes
• Toluene
• Trichloroethylene
• Xylenes

• 1, 2, 4 Trimethylbenzene
• 1, 4 Dichlorobenzene
• Ethylbenzene
• 2 Butoxyethanol
• Estriol

2. Baubiologie Rosenheim Institute certification

The IBR, Institute for Biologically Sound Construction, is a German institution that certifies healthy and environmentally sustainable consumer construction products, and includes a series of tests that measure the emissions of a product, including:

• Radioactivity
• Biocides
• Polychlorinated biphenyls
• Heavy metals

• VOC
• Formaldehydes
• Biological compatibility
• Electrostatics

3. Eurofins Indoor Air Comfort certification

This certification systems classifies construction products into two categories: Standard level “Indoor Air Comfort – certified product”, which shows compliance with product emissions criteria established by EU authorities, and Higher level “Indoor Air Comfort GOLD – certified product”, which shows additional compliance for product emissions with the criteria set by the most relevant ecolabels and sustainable building organisations in the EU.

What you don’t measure you can’t improve

There are several testing laboratories in Spain for the measurement and certification of materials and their VOC emissions, such as Tecnalia, and SGS. What if I want to measure the indoor air quality of my home without spending a fortune? There’s affordable equipment with reasonable accuracy, such as the range of MICA sensors, manufactured by Inbiot. They measure VOC’s, formaldehydes, ozone, suspended particles, radon gas, CO₂, temperature and relative humidity.

The following figure shows measured data from a MICA sensor of formaldehyde concentration in a bedroom over the course of a week.

According to the technical standard of measurement in Baubiologie SBM2015 for rest areas, values above 100 μg/m3 are already extremely significant. “The search for emission sources is a bit like looking for a needle in haystack, based on the data and measurements. But you can gradually discard sources until you find the culprit” says Maria Figols, Project Manager at InBiot.

Better living with less emissions

Creating healthy indoor environments is clearly on the agenda, with the construction sector on centre stage. Choosing the right low-emission materials will improve indoor air quality and can help reduce illness for occupants, in the short, medium, and long term. Using products with some of the certification systems shown above is a good place to start. Alongside emissions, these kind of certification systems also assess the environmental impact of a product, making sure they don’t pose a significant hazard during manufacturing, deconstruction, recycling or waste treatment phases. Reducing the source of indoor contaminants should always be the first step. The second step- and equally important- is controlled and efficient ventilation.

Acknowledgements

To Maria Figols and Xabi Alaez from InBiot for their contributions.

Bibliography

Keys to the Passivhaus standard: what is it and how to achieve it?

The Passivhaus standard is a voluntary energy certification standard for new and retrofitted buildings, aimed at providing maximum comfort for occupants, excellent indoor air quality and near-zero energy consumption. It was developed in the 90’s by the Passivhaus Institute in Darmstadt Germany, and it has since been expanding across the globe. The current climate crisis is increasingly bringing the standard into the limelight due to its radical no-nonsense approach, rooted in buildings physics, a rigorous design process and an emphasis on proper site supervision and commissioning. The objective is to close the so-called “performance gap” (where buildings fail to perform as predicted), making them fit for purpose, comfortable, healthy, and resilient. A Passivhaus building typically consumes up to 90 % less energy than a conventional building.

This article, written by Oliver Style, explains some of the key aspects of the Passivhaus and what you need to do, to achieve certification.

Passivhaus: the Basic Principles

It is often said that the standard is based on the following 5 principles:

• High levels of thermal insulation
• High performance windows
• Efficient mechanical ventilation with heat recovery
• Air tightness
• Absence of thermal bridges

Although this simplification can make it easier to understand what Passivhaus is all about, a Passivhaus building requires a holistic design process where the whole is more than the sum of the parts… and there are many parts. So, beyond the 5 basic principles, there are several other factors that are important for achieving certification and making sure a building does what it says on the tin, especially in warm climates, namely:

• External shading devices to reduce solar gains and avoid summer overheating 
• Efficient Domestic Hot Water (DHW) systems, equipment and lighting: to reduce primary energy consumption and reduce internal heat gains in summer (helping avoid summer overheating).
• Efficient heating and cooling installations
• In climates with sufficiently low minimum night time temperatures: Natural night ventilation combined with thermal inertia, to remove heat from the building without relying only on active cooling.

A building designed to have very low heat losses in winter, will also keep heat out in the summer: if you fill a vacuum flask with cold water in the summer, the water will stay cool for longer than if you just left it in outside in ambient warm air.  However, once the heat is inside, it will logically dissipate more slowly due to the high level of thermal protection. That is why it’s particularly important to go beyond the “5 principles” if you want to avoid overheating problems, which will increasingly become an issue as summers get warmer due to global warming (Figure 2).

PHPP: “Passive House Planning Package”

For the design of a Passivhaus building, the PHPP (“Passive House Planning Package”) tool is used, a quasi-steady-state single zone energy modelling program, based on a series of spreadsheets in Excel, that provides monthly and annual energy balances. The algorithms in the tool are based on a number of ISO standards, mainly in the monthly method of EN ISO 13790, now replaced by ISO 52016 0.

The PHPP has been calibrated with thermodynamic simulations carried on with the DYNBIL tool, developed by the Passivhaus Institute, itself calibrated by extensive validations with monitored data.

PHPP stands out for its simplicity compared to dynamic tools and can be used to model (albeit in a simplified way) a wide variety of active and passive systems, at a very affordable price. The results indicate the energy balance of the building in both summer and winter, yielding results of heating and cooling demands and total and final and primary energy consumption. Although a dynamic tool is- in principle- more accurate, the large number of parameters and input data increases the possibility of modelling errors and requires experience and time for accurate use. In energy simulation, it is sometimes better to be approximately correct than precisely wrong…

Passivhaus for new build

The Passivhaus standard for new buildings is performance based: i.e., it doesn’t limit thermal transmittance values ​​of the different construction elements, but establishes maximum energy demands and energy consumption, calculated with the PHPP. The air infiltration level cannot exceed 0,6 air changes per hour (ACH) at a pressure difference of 50 Pascals, measured with an on-site test, known as the “Blower Door” test.

The limiting values for heating and cooling demands and total primary energy consumption, are shown in Figure 3.

There are 3 classes of certification: Classic, Plus and Premium. Classic does not have renewable energy generation. To get to Plus, you have to generate ≥ 60 kWh/m2·a of renewable energy (references to the building’s footprint)- typically at least as much as what the building consumes. To reach Premium, the building must generate ≥ 120 kWh/m2·a (or 4-5 times more than what the building consumes). This is shown in Figure 4. The advantage of this approach is that energy demands are reduced first, before considering on-site generation of renewable energy. This differs from the conventional net-zero energy approach, which inevitably favours buildings with very large roofs on which a large solar PV generator can be installed, leading to buildings with a poor form factor (the ratio of enclosed envelope area to useful floor area), higher losses and where on-site renewable energy generation is prioritised over reducing energy use.

PHI Low Energy Building

If the above requirements are not met, a building can be certified as PHI Low Energy Building, complying with less stringent requirements, shown below in Figure 5.

Passivhaus for retrofitting: EnerPHit

For the retrofitting of existing buildings, there is the EnerPHit seal, which offers two ways to achieve certification:

• EnerPHit, Demand Method: performance based, with the requirements shown in Figure 6
• EnerPHit, Component Method: prescriptive, with the requirements shown in Figure 7

For both methods, an air tightness test result of N50 ≤ 1.0 ach must be obtained. The Classic, Plus and Premium classes are also applicable to the EnerPHit standard.

Overheating risk in summer

For certification, overheating risk is assessed through one of the two following methods:

• With active cooling: the limiting total cooling demand must be met (sensible + dehumidification), calculated with the PHPP, with mechanical systems capable of maintaining thermal comfort at all times (according to ISO 7730), with an operating temperature ≤ 25 ºC and a maximum of 10% of the hours in the year with an absolute indoor humidity ≥ 12 g/kg dry air.
• With passive cooling:  the maximum overheating frequency must be met, calculated with the PHPP, with a maximum of 10% of the hours in the year with an indoor operating temperature > 25 ºC.

In the case of passive cooling, it is important to stress that 10% of the hours of the year are a total of 876 hours with an indoor operative temperature above 25 °C (the whole month of August, for example). Therefore, the recommendation is not to exceed 5%, with a good design objective being 2 – 5%, shown in Figure 8.

To reduce the risk of overheating where no active cooling is available, it is important to perform stress tests of extreme climate situations with the PHPP. For this purpose, Jessica Grove-Smith of the Passivhaus Institute has developed theSummer temperature tool[2], which adjusts the summer temperatures in the PHPP climate file, taking into account the urban heat island effect and the increase in temperatures according to IPCC’s predictions (Figure 9). This feature will be integrated directly into PHPP version 10.

For tertiary buildings and/or buildings with areas exposed to very different indoor and outdoor conditions, it is advisable to accompany the PHPP calculation (a single zone tool) with a dynamic multi-zone calculation, to analyse specific zones that may be more susceptible to overheating (for example, the top floors in a tall building with west-facing glazing).

Additionally, if the building does not have an active cooling system, it is important to test assumptions regarding user behaviour, for example, in relation to closing blinds and opening windows at night for natural ventilation. Is it realistic to think that a person will sleep all night with the blinds open, all windows fully open, and all interior doors open? It is more likely that occupants will close the blinds before going to sleep so the sun light doesn’t wake them up in the morning. If you live in an urban area, you might want to close all windows facing the street to avoid noise. All this reduces natural night ventilation flow rates and the amount of heat that can be extracted from the building.

Although the goal is always to reduce dependence on active systems to maintain comfort, in most cases, some active cooling in summer is advisable. Fortunately, the summer is also the time when there is the most solar radiation, which means active cooling energy consumption can be directly off set with on-site renewable energy production.

Air tightness: the “Blower Door” test

Central to the Passivhaus standard is the “Blower Door” airtightness test, that measures air infiltration through a piece of equipment that pressurizes and depressurizes the building. Preliminary tests must be carried out before the interior finishes are completed (to detect and correct leaks, if found), together with a final test, according to the EN 13829 [3].

The “Blower Door” test is a clear indicator of build quality. What are the advantages of reducing air leaks?

• Reduces energy losses and heating bills in the winter
• Reduces the entrance of moisture in warm-humid climates, thereby reducing dehumidification cooling consumption and cooling energy bills
• Improves comfort, eliminating air drafts
• Improves people’s health by preventing the entry of radon gas, suspended particles and other pollutants from outside

An air tightness strategy must always be accompanied by controlled mechanical ventilation, to ensure good air quality and the elimination of moisture and pollutants generated inside the building.

An existing building will typically have an infiltration level of n50 ~10 ach. A certified Passivhaus has an n50 ≤ 0.6 ach. The Spanish CTE Building Regulations, in the 2019 update, establishes a limit for air infiltration of n50 3 ach and 6 ach according to the compacity of the building (Figure 10).

Audits and certification: quality assurance from design to completed building

The certification process and auditing begin in the design phase and conclude when on-site construction is finished. Certification can only be carried out by the Passivhaus Institute or an approved Building Certifier. As an external agent to the project, the certifier verifies that the project complies with the standard and that construction has been completed as planned, accurately reflected in a the PHPP model. The client needs to supply detailed as-built architectural and service drawings, photographic documentation showing the execution of all elements related to energy and air tightness, the final certificate of the Blower Door test, the ventilation system commissioning results, together with a letter signed by the Site Supervisor, indicating that the project has been built as designed.

Passivhaus and health

Although the standard does not specify which materials you use in a building, the PHPP manual explicitly recommends the use of low-emission materials, to reduce VOC’s (volatile organic compounds) in indoor air.

To ensure good air quality, the correct sizing of the ventilation system at design stage is checked. Once installation is completed, the commissioning of the system and the measurement and adjustment of flow rates in all supply and return valves is mandatory.

The goal is to create healthy, comfortable, efficient and resilient buildings, closing the performance gap between projected and real-life performance.

Bibliography

• [1] EN ISO 13790, Energy performance of buildings – Calculation of energy use for space heating and cooling. This standard has been revised by ISO 52016-1:2017
• [2] Criteria for the Passivhaus, EnerPHit and PHI Low Energy Building Standard, version 9f. 15.08.2016 1/30. 2016 Passive House Institute.
• [3] Passive House Institute Summer Temperature Tool, Available at: https://passiv.de/en/05_service/02_tools/02_tools.htm
• [4] DIN-EN 13829, Thermal performance buildings – Determination of air permeability of buildings – Fan pressurization method. (ISO 9972:1996, modified).

Radon gas: invisible and lethal. What is it and how to prevent it?

Radon gas is a naturally occurring radioactive gas that can enter buildings. It is currently the second most predominant cause of lung cancer after tobacco. It’s colorless, tasteless and has no smell, and is produced from the natural radioactive decay of uranium, present in many types of soils and rocks.

How is radon gas measured in a building?

Becquerels (Bq) is the measurement of radioactivity. A becquerel corresponds to the transformation or decay of 1 atomic nucleus per second. In the air, radon concentration is measured by the number of transformations per second in one cubic meter of air (Bq/m3).

The national annual average reference level, set out by WHO in its “WHO Handbook on Indoor Radon: A Public Health Perspective”, is 100 Bq/m3. If this level cannot be reached due to country-specific conditions, the level should not exceed 300 Bq/m3.

Radon measuring devices are divided between passive and active detectors, with an uncertainty range of between 8% and 25%, depending on the type of device. The most common devices are usually passive, logically cheaper than active ones, and incorporate trace sensors for alpha particles, or ion electret chambers, to measure radon concentration.

As the concentration of the gas in indoor air can increase significantly in the short term (hours), is recommended to take long-term measurements (for example, 3 months). If the building has a ventilation or HVAC system, it is convenient to take measurements with the system on and off, in both cases for a long period time.

There are low-cost types of equipment such as the RadonEye RD200, or Airthings Wave, shown in Figure 2 and Figure 3.

Radon gas and the Spanish building regulations

In 2019, and for the first time, Spanish building regulations established the scope and requirement of radon gas with a reference level for the average annual radon concentration inside habitable premises of 300 Bq/m3 (triple of what is recommended by the WHO).

Applicable to all new buildings, extensions, changes of use, or refurbishment of existing buildings, the regulations require the following measures, according to the risk area:

Level 1:

• Radon barrier between living spaces and the ground
• Ventilated air gap between the living spaces and the ground

Level 2:

• Radon barrier between living spaces and the ground
• Additional protection system:
  • Ventilated air gap between the living spaces and the ground
  • Ground depressurization system that allows the gas to dissipate from the ground.

The radon gas map of Spain according to the HS6 level 1 and 2 classification is shown in Figure 4.

How does radon gas enter a building and how to avoid it?

Radon enters a building through the fissures and openings in the envelope, especially in parts of the building in contact with the ground (slabs, basement walls, etc.), where the concentration of the gas is generally higher on the floors above (ground and first floor, etc). This is accentuated in the building during the heating period, where warm air rises, and the stack effect creates air infiltration of air on the lower floors (and exfiltration on the upper floors).

Radon gas entry is reduced and/or eliminated by a gas-resistant membranes, with a diffusion coefficient against radon less than 10-11 m2/s. An example is shown in Figure 5. The barrier must be continuous, taped and sealed at all joints and service penetrations. It is advisable to conduct a Blower Door test during the construction phase to detect leaks and repair them.

In Level 1 areas, as an alternative, it is possible to build a ventilated crawl space between the living areas and the ground, although it is a less safe solution than a radon barrier.

In Level 2 areas, the radon barrier is essential, along with a ventilated crawl space or a ground depressurization system.

The ground depressurization system consists of installing a network of perforated intake ducts, with mechanical extractors that conduct the air to the outside, above the building. This system has the same drawbacks as the ventilated crawl space and depends on a mechanical system.

Although few epidemiological studies have been conducted on the possible link between radon gas in drinking water and the incidence of stomach cancer, a study by Kyle P Messier and Marc L Serre of the University of North Carolina, USA indicates that increases the risk of stomach cancer. Therefore, water becomes a double entry route, by ingestion of contaminated water or by breathing radon gas evaporated from drinking water. Under normal circumstances, the amount of radon inhaled when breathing is greater than that ingested when drinking.

Radon in drinking water can be reduced and/or eliminated by employing granular activated carbon filters, but the filter itself can accumulate radioactivity and should be located outside the thermal envelope (in a garage, for example), taking care of its treatment as toxic waste at the end of its useful life.

Study of the incidence of radon gas in 122 homes in Ireland

Barry Mc Carron, Xianhai Meng, and Shane Colclough conducted a radon gas measurement study on 122 homes in Ireland, 97 Passivhaus-certified homes, and 25 conventional homes (reference). The results can be seen in Figure 6. The average level of radon gas inside the Passivhaus dwellings was below 40 Bq/m3, both on the ground and first floors. However, in conventional homes, the average level was 104 Bq/m3 on the lower floor, and 69 Bq/m3 on the first floor.

The differences clearly show the effectiveness of airtight construction to prevent the entry of radon gas: one of the requirements of the Passivhaus certification is to have a level of air infiltrations n50 ≤ 0.60, verified by an air-tightness test.

But not only this, Passivhaus homes have a mechanical ventilation system with heat recovery, which constantly renews the air, eliminating stale and polluted air, and introducing fresh and filtered air. This can be seen in the graph in Figure 7, where Professor Walter Reinhold Uhlig of the HTW University of Dresden, measured radon gas in a Passivhaus dwelling with a mechanical ventilation system on and off. With the ventilation turned off, in certain rooms the radon level increased to 350 Bq/m3, having remained below 100 Bq/n3 with the ventilation working.

Considering how lethal it is, radon gas has- surprisingly- gone unnoticed among many professionals in the sector, public administrations, and health professionals. Thanks to increased awareness and the update of the Spanish building regulations, it’s an issue we clearly can’t ignore: we need to prevent radon from entering our buildings, and ensure correct ventilation! The empirical results shown above indicate that an air or radon gas barrier, together with a mechanical ventilation system, is a highly effective combination to reduce the entry of radon gas into a building and thus protect the health of users.