Undertaking a self-build project is not for the faint-hearted and I always take my hat off to anyone considering this route. You have to acquire, almost overnight, technical research and project management skills and the ability to make, often quick, decisions on hundreds of minor, yet crucial, things. Of course, the upside is that you end up with a bespoke home ideally suited to the needs of your family and one that will hopefully bring you much enjoyment and comfort in years to come.
Which is why I’d like to make the case for making your self-build a Passivhaus. Passivhaus is the leading international low energy building standard and offers superlative levels of comfort, air quality and energy savings to its occupants. The standard is based on the sound principles of building physics and has been tried and tested for 25+ years so there is a mass of evidence that it works and that buildings certified to the Passivhaus standard perform as designed.
Passivhaus design relies on maximising the use of super insulation and stringent levels of airtightness. Special attention is paid to continuity of insulation and airtightness at key junctions in the building, such as between the wall and floor and between walls and windows. This is combined with optimising levels of passive solar gain and the use of mechanical ventilation and heat recovery systems for good levels of ventilation while also recovering heat lost through ventilation. The result is a healthy and comfortable home that requires minimal heating.
Passivhaus buildings achieve a 75% reduction in space heating requirements, compared to standard practice for UK new build. The Passivhaus Planning Package (PHPP) software tool is an accurate design and compliance tool and extensive monitoring of Passivhaus buildings shows that the they perform as designed. This offers self-builders an extra layer of quality assurance. You want your dream eco home to actually cut carbon emissions and bills as is promised.
Comfort is a huge element of the Passivhaus standard. Attention to detail on airtightness means that draughts are virtually eliminated in a Passivhaus and no down draughting from cold surfaces. By keeping all surfaces warm there is no cold radiance from surfaces and also no temperature differential between floor and waist level – avoiding the ‘cold feet effect’. Attention is also paid to the need for ‘summer comfort’ and careful modelling of the house to avoid summer overheating. The MVHR system good internal air quality due to continuous ventilation with no mould growth, low CO2 levels, and good extraction of pollutants from incoming air.
Sometime Passivhaus is portrayed as very technical and complicated but in reality it relies on very simple technology. The mechanical ventilation with heat recovery systems use a simple low energy fan to move air around the house, which can be easily repaired or replaced at the end of life. The MVHR systems do not require annual maintenance check-ups only regular filter changes to keep everything working smoothly. As the focus is on the building fabric itself, a Passivhaus effectively runs itself, with little input needed from occupants.
How much extra does Passivhaus cost?
The additional costs of building to the Passivhaus standard can vary quite widely. Keeping costs down during a Passivhaus self-build requires good planning and design and mainly ‘keeping it simple’. The Passivhaus methodology needs to be incorporated from the very beginning and ideally you need to work with architects or a consultant and contractors with Passivhaus training and experience, or at the very least a real willingness to learn. Recent research by the Passivhaus Trust has found that add-on costs, for an experienced team, of building to Passivhaus standard can be around 8% but they fully expect in the future that this could come down to around 4% with economies of scale and as the industry gears up.
By choosing the Passivhaus standard you are NOT restricting yourself as to design styles for your self-build home. You can use any construction type, from ICF to strawbale, and any design type from contemporary and minimalist to traditional and cottagey.
You will, however, need to think about the ‘heat loss form factor’ and how to create a compact house design. The heat loss form factor is the ratio of thermal envelope surface area (that can lose heat) to the floor area (that gets heated). It is a useful measure of the compactness of a building. Generally, the more compact a form, with few ‘sticking out’ features, the easier it will be to make it energy efficient. Keeping the form of the house simple has the added benefit of keeping design and build costs down.
By going down the Passivhaus route, you get to build your dream home with quality assured comfort, energy savings and air quality, while also creating an eco exemplar project that is helping to make the world a better place. What’s not to love?
Chayley Collis, Communications Manager, Green building Store Products and support for Passivhaus and low energy buildings www.greenbuildingstore.co.uk