PHPP question - Windows for a Passive Build

BigGeorge

Am looking at windows for a passive build & there appears to be a large price increase when you go for the whole 0.8 U value certified window thing.

Have anyone any experience on using the PHPP to increase the U value of the walls ( which is fairly inexpensive) & to relax the standard on the windows ( say to a 1.0 or 1.1 U value window) whilst at the same time staying within the 15 PHI target required for certification

MicktheMan

While heat conduction through the window is obviously important in any build and especially in a passive house, the internal window surface temperature is equally important from a comfort point of view. The need for a conventional heating system is eliminated in a passive house and the window internal surface temperature has a lot to do with this, not just the level of heat loss through the building envelope and the airtightness level.
What I'm trying to say is that there is a lot more to a ph than just the 15kWh/m2/yr and 0.6ACH!

beyondpassive

Hi Big George,

Its possible

The price of glass for the 0.56-0.6 triple glazed not significantly more expensive than basic treble glazed. I've run scenarios looking at 9.6 frame value as compared to 0.7 certified frames. As with everything in passive it is related to the two big equations on which everything depends, the ratio of treated floor area to volume and the ratio of external envelope to footprint. Get them right, ie. close to a shoe box shape orientated to maximise solar gain without excessive overheating, and the windows and fabric are easy.

The difference in cost between upgrading to higher standard windows is easily justified. The quality of the finish and the sharpness of the profiles, the smooth operation of the mechanisms is what you get apart from the improved thermal performance. Fabric improvements can be costly in labour costs along with the additional materials. So I guess its not straight forward. Thats where the PHPP is quite handy, you can compare different scenarios and work out how much bang you are getting for your buck. Once the model is defined you can try out any number of scenarios. Takes the guesswork out of it.

The majority of clients get the fabric to about 0.17 and go for the certified window, with treble glazed rooflights and sometimes a lower performance slider screen wher the pane size is wider than 2.4 meters. You wont know whats best for your own situation untill you model it up.

sas

The price difference I've found between aluclad and timber only windows is pretty significant.

38k (Larch) vs 45k(Aluclad pine) on one occasion.

Obviously I don't know what your tolerance for maintenance is but it may be worth investigating.

Note however that the price difference really only applies if you want the same finish on the timber inside and outside i.e. black outside means black inside.

If you wanted black outside and varnished timber inside the price falls straight back into line with Aluclad due to the significant increase in labour.