Passive Houses are lauded for their low energy use, but does that come at the expense of occupant health?

According to Bo Gleditsch of the Norwegian asthma and allergy association, they can.

“We get many questions about passive houses,”  he noted. “They are almost hermetically sealed houses where the air does not change. This causes dust to accumulate and high temperatures.”

Regulations in Europe will require all new buildings to be nearly carbon neutral by 2020. Passive Houses are one way to reach that target. However, Gleditsch said, “in our eagerness to solve an environmental problem, we are causing a health problem.”

The Passive House standard was developed in Northern Europe and is optimized for that climate, with specifications for total energy use, heating and cooling energy use, and air-tightness of the structure. The US branch of Passive House broke away from the German branch and has developed its own standards for North America that vary the requirements by climate. Nonetheless, both versions of the Passive House standard require a very tight structure combined with extremely low energy use.

The standard does not prescribe methods or materials, but typical approaches have evolved to meet the three mandatory standards. Those include using thick insulation, and usually call for an active ventilation system, such as a heat-recovery ventilator.

Another technique that aims to reduce energy use is earth tubes. Tubes buried under the house or elsewhere on the site are used for the fresh air supply and are connected to a heat-recovery ventilator. Their location in the soil helps to cool the incoming air in hot weather, and warm the incoming air in cold weather. In theory, this simple approach lessens the amount of supplemental heating and cooling needed for a comfortable indoor temperature.

Problems can arise when they don’t perform as expected, or are not installed as designed. In those cases, earth tubes can harbor mould and condensation, leading to degraded and unhealthy indoor air. The air-tight construction and thick insulation required in a Passive House may then exacerbate air quality problems resulting in health issues for the occupants.

To cite one example, a home in Belgium was eventually declared uninhabitable after the family living there experienced myriad health problems immediately after moving in. Investigators determined that the earth tubes had standing water in them, leading to mould growth. The tubes also contained construction dust.

In addition, the air flow created by the heat recovery ventilator underperformed design specifications, and mould built up on the HRV filter.

Another problem with this home is the wall design, which used an unventilated air space between the exterior brick veneer and the wall sheathing. Investigators determined that after rain, some of the moisture absorbed by the exterior brick cladding migrated inward where it dampened the wall sheathing. This process is known as “solar driven vapor flow,” which increases with temperature. The investigator concluded that high relative humidity, along with high temperatures, facilitated the release of formaldehyde from the sheathing into the interior of the house.

These issues caused health problems for the family, including respiratory problems, diarrhea, muscle aches, and headaches. The earth tube contractor attempted to correct the problem twice, but without success, and the home was declared uninhabitable about two years after it was built.

In this case, the Passive House approach coincided with other problems, but was not the cause of the problems. Any nearly air-tight home would be susceptible to air quality issues caused by mouldy, humid incoming air, along with formaldehyde off-gassing. Those air quality issues were the direct result of design and construction flaws in the earth tubes and the walls.

The investigator, Dr. Hugo Hens, a professor in the Building Physics unit of the Department of Civil Engineering at the University of Leuven in Belgium, drew some conclusions in his paper, Passive Houses: What May Happen When Energy Efficiency Becomes the Only Paradigm.

“Though solely promoted as energy savers, their impact on energy consumed is too minimal [for] the possible risk they create in terms of degrading supply air quality,” he remarked.

Martin Holladay, a noted writer on green building, wrote in Green Building Advisor that “Homes with earth tubes and vapor-permeable exterior sheathing can perform well — but only if the designer uses a whole-building approach that considers moisture movement from all angles. Moreover, if a builder makes installation errors, all bets are off.”

  • I think the statement "They are almost hermetically sealed houses where the air does not change" is inaccurate, being that a passive house is required to have a ventilation system, therefore the air does change As a matter of fact the air quality in a passive house is generally much better than a "normal" house. Furthermore the article title should read "Do badly constructed house cause health problems?" The examples given are examples of bad construction practices, the fact that they are passive houses is not the reason for the resulting health problems.

  • Good comments from Keiran & Fiona.

    The Belgium example cited is a well-known disaster and *not* a certified Passivhaus.

  • Hello Steve

    It's important in this topic to be really clear, as there is so much confusion around sustainable building design and the word "passive".

    First, it should be noted that Brussels has now mandated the Passive House Standard for all new buildings and retrofits. They are leading Europe.

    Second, a certified passive house is better than, and not the same as, a "passive house". Passive house can mean anything. People can seal up their buildings, add a bit of insulation, and call it passive. Without proper meticulous design, using the PHPP (building physics program), there are risks inherent in a patchwork approach.

    I have heard of many houses and apartments in Australia with mould problems for a variety of reasons (see my last article on mould and thermal bridges). None of these are certified passive houses.

    Third, earth tubes are not a passive house component.

    When I was researching for our certified passive house design, I discovered that Dr Feist from the International Passive House Institute did not recommend earth tubes, for the reason you state. There are too many issues with potential mould sitting in the tubes and being brought into the home.

  • Ventilation is the 1st, (first) consideration in the design of Passive Houses (PH), has been, and still is, as expressed in all the PH classes of which I know. The founder of Passive House Institute United States (PHIUS) starts the classes with the absolute need for the ventilation system. The author should visit more real PH careful not to skip on the potentially wet floor caused by the PH devotees drooling over the ventilation system. If concerned, anyone can open the properly installed windows. PH optimizes materials and maximizes comfort utilizing the latest in building science.

  • Great article, thanks

  • Opening windows and doors can overcome all humidity problems in most climates.
    Since the Planning systems have taken control of windows and doors, that no longer applies.
    Awning windows that open only a 100mm at the bottom can have you cursing on hot humid nights unless other action has been taken. The worst house build today is no way as bad as the slum housing of inner Melbourne that lasted into this century.
    Anyone walking into a damp putrid terrrace house that was designed for Northern Englands climate with small windows that 100 years of painting have made unopenable, would vomit or collapse.

    Count your blessings, and open the windows when the sun is out; if you have openable windows in your new house or flat. If you do not, curse the Planner and buy a heater or air conditioner.
    If you die of a lung infection or cancer, at least the neighbours will not see you through through the obscure glazed unopenable windows gasping for air.

    • In a well constructed passive house there is no reason to open your window as the Ventilation system will keep the entire property at the optimal temperature all year round. This article cites poor construction. Obviously you can open your windows, it just shouldnt be necessary if the ventilation system is installed correctly.

  • We air pressure tested several homes with surprising results.

    They were all brick veneer construction. The internal fit out was similar. however the spread of results was radically different. The worst house had the equivalent of having a two inch air gap at the base of perimeter of the building. Basically this house was a wind tunnel.

    The best house was sealed up to almost no air movement. To look at the houses they looked very similar

    In pulling apart the results we found methods of construction make a massive difference to the end result.

    The good house used sealed awning windows, doors with door seals, power points were sealed. Draft excluders were used in wet area fans. They used standard light fittings.

    The poor house had alloy sliding windows. Poorly sealed doors. gaping holes around all power-points and switches, fans were open, and they had a massive amount of down-lights.

    These houses were built by the same builder under slightly different specifications.

    There is currently no need to measure the houses.

    The MBA is hot on the topic. The HIA put their head in the sand.

    This was a while ago, so things may have changed, but its a very serious problem. Someone will die!!!!

    Actually they already have. I seem to recall that there have been several cases of death related to this topic. One i clearly remember was carbon dioxide asphyxiation due to a space heater. Anywho , my two cent worth

  • All of the author's examples deal with Passive Houses that have design defects — Or ventilation systems which are installed poorly. Similar mold issues can be found in MANY conventional homes where design mistakes are made. These issues are not singular to Passive House construction techniques and more to do with poor building science as a whole. Most Passive Houses include a well designed E/HRV system which actually leads to superior indoor air quality when compared with standard construction techniques.

    • Agreed, Luke, which is why I wrote, "In this case, the Passive House approach coincided with other problems, but was not the cause of the problems."

  • This raise further attention for install a proper HRV/ERV system in Passive House to achieve design performance, even some of the ERV/HRV unit get the certified PH component, its only representing efficiency/unit leakage/electrical efficiency etc. That far from running the whole system very well, proper ventilation system need also well design of ductwork system and acoustic parts, and last but not least, Commission of the whole system to make the airflow balanced.

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