How much window area can i have in passive house?
I understand Ecohome doesn't go by "old" rules of thumb 7-12% of floor area for direct gain or thermal mass. I have a 300 square foot area with direct gain (no thermal mass on floor) and another 300 sq ft of slab for my walk out basement. The orientation is south. I plan to use high performance windows, but not triple pane.
Are you just planning to build just using Passive House targets and performance standards or are you going for certification through a Passive House institution? A Passive House designer will be the one to determine the overall design and how many windows can be accommodated and still meet the performance criteria. This page will be helpful I think –
All you need to know about Passive House certification
But to address your question about windows – there is an overall performance target that needs to be met for any Passive House building, so the more windows you have in your design, the more you will need to beef up the insulation levels of other parts of the home. You mention using ‘high performance’ windows, but that they aren’t triple pane. In any cold climate, a window that isn’t triple pane just does not fall into the category of ‘high performance’, and it would be a smart upgrade in any home but particularly a Passive House, read here about windows to make your best selection, triple pane is very much worth the added cost–
How to choose the best windows for High Performance Homes
As an example of how the total window surface area and quality of windows affects design, here is an example - a Passive House we know of that has significant glazing required 24 inches of sub-slab insulation to make up for the loss through windows in order to achieve certification. There is simply no place on this globe outside of besides the North Pole where 24 inches of rigid insulation makes any sense. It is a bit of a glitch in the Passive House system regrettably, where the underlying goal - to reduce climate change causing emissions from buildings - goes right out the window in search of certification. You would be better at that point to forgo certification and reduce the insulation levels since there are more emissions from manufacturing that amount of insulation than it will ever save in the lifespan of a home. So... limit your window use if possible, and try to upgrade to triples!
Thanks a million ...totally agree about certification. I just want a passive "approach" I thought I read on ecohome that dual pane with suspended film is as efficient as low e triple
Thanks Tony, and suspended film is an entirely different story. You hadn't specified that so I assumed you were talking simple double pane windows and its not likely that many houses would achieve PH certification with just that, or is it even following the general principles. So yes, Suspended film windows act like triple pane windows, or better even as they can have several films. All around I say go for it - I look forward to trying suspended films soon myself, and I think aiming for Passive House performance but not worrying if you don't quite make it is the best way to go!