We moved into our self build two years ago, as an architectural designer I designed and specified the build throughout to be as close to a passivhaus standard as possible whilst utilising traditional build methods i.e masonry cavity wall, beam and block floor etc to appeal to as many builders as possible for build speed and tendering, I needed to get the house built v quickly for our disabled son and to get it done before brexit pushed material prices up, that was the plan and then the pandemic hit which made things interesting. Anyway, some rambling thoughts to hopefully help you out:
Our house is pretty airtight (2.5) considering this type of build is prone to being leaky. We have an ASHP, MVHR, UFH, Solar PV and rainwater harvesting (wc’s and washing machine). Triple glazed windows/rooflights and increased thermal insulation throughout. We were very keen not to have a new build feel internally (white box) and do have some rooms with carpets – lounge, study and all bedrooms. Oak window cills, window and door frames with a light grey finish, most importantly – colour on the walls! Have fun with it.
Regarding internal comfort, we were coming from the complete opposite, a 17th century cob cottage which we renovated. The cottage was always cold, damp and draughty. The new house is obviously the complete opposite and has taken us a while to get used to, it is far warmer and dryer than we were used to but not unpleasant – just different. The air always feels fresh inside and its really nice not worrying about mould/condensation anymore. I would not hesitate going for this spec again and now have the info to pass on to my clients. In terms of how we use the house, generally we have windows and doors open during the summer months day and night as you would in a traditional house (except in a heatwave). The MVHR is kept running all year – summer bypass mode during warmer months, in the colder months we begin to close the house up more so we then utilise the heat recovery. In winter we have found the MVHR to create quite a dry environment despite hanging clothes to dry in one of the bedrooms over night. If I was doing another build I would be speaking to the MVHR designer about how this can be factored in (Green Building Store designed ours and were excellent). Make sure the MVHR is designed with acoustic baffles to each habitable room, this reduces the risk of noise. We cannot hear our system at all.
Internal temperatures stay around 21 to 22 most of the year, dropping to 19 during the colder months with some heating. The biggest issue with a well insulated house is the potential for overheating, I put our design through the passivhaus software (PHPP modelling) and reduced the areas of glazing considerably, choose good quality triple glazed windows (G value important, less transmission = reduced overheat risk). Keep rooflights to a minimum, we have two with external roller blinds that are electrically operated and can be closed during heatwaves. Carpets/underlay – just go for ones that are suited to UFH, it wont be quite as reactive but it will be fine.
Unlikely that you will need to run the ASHP flow temps that high, were at 28 to 38 (weather dependant).
Cost seems about right.
Some more photos of builds/bikes on my insta if interested