passivhaus: frequently asked questions
Is the standard only applicable to houses?
No. The standard is very versatile and applies to all building types. There are many different types of certified passivhaus buildings in existence in the world today, from schools and offices, to banks and even a recently certified swimming pool.
Will the building really be warm enough without a conventional heating system?
Yes. The design temperature for the whole of the indoor space is 20 degrees C (maintained even when it drops to -10 degrees C externally), however this can be adjusted either up or down according to the occupants preferences. There are many examples of certified passivhaus buildings in many different climates that have been monitored and occupied for many years, proving that the standard is flexible and really does work, even despite a variety of occupant habits and lifestyles!
Can I open my windows in a passivhaus building?
Yes. Just like in a conventional building, opening the windows in a passivhaus simply lowers the indoor air temperature. The principle difference is that in a passivhaus building there is no need to open windows to improve the air quality due to the MVHR system. Opening windows is a key part of the design for additional ventilation in summer to counteract the risk of overheating.
Does the ventilation system cause draughts and is it noisy?
No. The ventilation system is very carefully designed and, when commissioned properly, should be installed to ensure very low air speeds at the various inlets and outlets within the building. There is barely any perceptible air movement until within centimetres of the outlets, and consequently no noise. This, coupled with the superior airtightness, ensure a draught free building.
Do I need a south facing plot?
No. Although a more open site to the south is helpful in increasing the available solar gain, it is still perfectly possible to construct a certified passivhaus building on a north facing or urban plot - this will influence the design, and a small additional heating input may be required, but it need not kill the proposal!
Does the building have to be a boxy shape?
Passivhaus buildings can be any shape you like, and be in any
architectural style. The important thing to remember is that the more
protrusions, overhangs, dormers, etc. that the building has, the more
potential area for thermal bridging there is, which means that this
added heat loss has to be compensated for elsewhere, by adding more
insulation to the walls for instance. All of this can in turn increase
the build cost, so it is worth considering the shape and form at a very
early stage in the design process.
Isn't it expensive to build a passivhaus building?
No. We don't believe it has to be so, and there are an increasing number of completed projects built to the passivhaus standards here in the UK that demonstrate this. The investment in higher quality building components is often off-set by the elimination of an expensive conventional heating / cooling system. Just like on any construction project, the key to reducing build costs is to prepare and plan in advance of construction starting. And of course, as with any other conventional building the reduced running costs for the future have to be taken into account and balanced with the initial investment.
Does the standard only apply to new construction?
No. It is possible to renovate some existing buildings to the EnerPHit standard, which is a slightly more relaxed set of values of the passivhaus criteria. Still considerably better standards than the current building regulations, this set of reduced criteria does make an allowance for the difficulties faced when trying to bring existing and historical buildings up to date in terms of energy efficiency.
Are there different criteria for different countries?
No. The criteria remain the same. The PHPP calculation is climate specific so a geographical location must be entered; the methods for meeting the criteria will vary depending on whether the building is in Siberia or Zimbabwe.