A catalogue of problems in Belgian Passivhaus homes has added to growing concerns over “performance gaps” in low-energy Passivhaus-standard homes in the UK.
Researchers at the University of Leuven’s department of civil engineering uncovered a range issues related to moisture build up and poor air quality in Belgian Passivhaus properties, caused in many cases by inadequate design, construction detailing and installation.
The 2012 report, Passive Houses: What May Happen When Energy Efficiency Becomes the Only Paradigm, found homes where airflow vents were left out by construction teams, leading to drastically reduced ventilation rates.
In other examples, installation errors related to mechanical ventilation and heat recovery units (MVHR), essential to the removal of moisture from air in airtight homes, caused problems with high humidity and air quality.
One home, built in 2005, was so badly affected it had to be condemned, after its occupants suffered from allergic health complaints, including excessive tiredness, coughing and itching skin.
Researchers measured extremely low ventilation rates at the property, much lower than standards required in Belgium, caused, in part, by the MVHR system which was not designed to the proper dimensions, but also by the contractor’s failure to build flow through openings into internal walls to enable air flow from the air inlets to the extractor vents.
“It’s a construction mistake we see happening again and again,” said Professor Hugo Hens, professor of building physics at Leuven. “The biggest issue is design teams, who must ensure that properties are properly detailed, with the correct wall and window interfaces. This often isn’t done properly in Passivhaus and other energy efficient buildings,” he said.
Poor air tightness detailing also had a serious impact on MVHR efficiency in homes, he added: “We have measured several MVHR systems and found typical mistakes: if the building is not detailed properly to be airtight, the efficiency of heat recovery drops very fast, and because MVHR fans continue to consume electricity, more energy is lost than saved.”
The Belgian findings are mirrored in a recent NHBC Foundation report, published on January 10, that looked at lessons learnt from Passivhaus building programmes in Germany and Europe.
The report said there were 165 Passivhaus buildings completed or under construction in the UK in 2012, but this is likely to treble to around 500 by the end of 2013. Worldwide, some 37,000 Passivhaus buildings have been constructed.
The study warned that demanding energy performance and quality assurance standards, as well as extra costs, make the standard unsuitable for the UK volume market.
It found that the cost of building a Passivhaus in Germany is just 3% to 8% more than building to German building regulations, while the German population also has a stronger interest in the environment and a general enthusiasm for higher specification products, it said.