Achieving an exceptional envelope could be quite cost effective if you didn’t like windows (surprising how often we hear engineers advocate for that solution). However, windows are rather important to the quality of life inside the house, so we are stuck with them.
We had always assumed we would use fiberglass windows from the beginning of the project with the only serious competitor to this being wood windows with the euro-style vented aluminum cladding on the outside. The more research we did, the more confirmation we received that fiberglass is indeed the best option for ultra efficient residential envelopes.
There are a number of manufacturers in the marketplace, but we really boiled ours down to 2 options – Thermotech Fibrerglass Fenestration from Ottawa ( http://www.thermotechfiberglass.com/), and Inline Fibreglass from Mississauga (http://www.inlinefiberglass.com/). As an aside, we also really liked the offering from Serious Windows (www.seriouswindows.com) but they did not have any kind of local representation. Both of these manufacturers build exceptional windows and it was hard to choose between them. In the end, it was the local dealer for Inline – confusingly called Thermotech Windows Ltd. ( http://www.thermotechwindows.com/index.html )– that was the deciding factor. We have worked with this dealer in the past on projects with good success and Arbnor helped us through the process. Inline is a much higher volume manufacturer than Thermotech so they can be slightly more cost competitive, but maybe not as flexible. The advantage of the local dealer is that he has some pull at the factory to ensure our relatively small order is not lost (we hope - Arbnor don't make us revise this post!).
If you are not familiar with the benefits of fiberglass, just go the Inline website and review the information there. This is not just sales talk - but is backed by good research from Building Scientists.
Since all orders are completely custom, we were able to select specific glazing for the different faces of the house. All windows are triple glazed – meaning 3 sheets of glass separated by a “warm edge spacer”, which is a non heat-conducting material. The spaces between the sheets are filled with Argon gas to further reduce thermal conductivity. Argon is a naturally occurring gas with no serious environmental impacts. On the southern façade, we chose coatings on the glass that would optimize heat gain from the sun. On the North we chose coatings that minimize thermal loss radiating back out. For our house, the East and West get very little direct sunshine – but they do get some, so we opted for solar gain glass on those walls as well. These windows perform very well. At the centre of the glass they are around R8 and the overall performance of an average sized window is around R5.
These windows are expensive. Our house is severely limited by code for windows on the East and West walls, and we are trying to limit the windows on the North for energy performance – so we really don’t have that many windows. In total we have 23 windows, averaging about 13 sq.ft. Each for a total of 300 sq.ft. Of window area. (This excludes our awesome folding glass wall on the south face – see other post). The total cost for our Inline windows is around $29,000. That works out to about $97/ sq.foot of glass area or an average of $1250 per window.
For comparison purposes, we asked Thermotech Windows to price our exact package in PVC from one of their other suppliers who provides “high quality” PVC windows (high quality and PVC don't really ever belong in the same sentence, hence the use of quotation marks). The price came back at $17,000. It is not an apples-to-apples comparison because there were a few windows which would have to be smaller if they were in PVC because the frames are not strong enough to hold the triple pane glazing unit over a long span, and the glass does not have a warm-edge-spacer. However, we can deduce that the premium for fiberglass is in the nieghbourhood of 60%. The thermal performance of the fiberglass windows is not 60% better than “high quality” PVC on the day they are installed, but they may last twice as long and will keep their performance much longer than the PVC windows. Also the use of PVC windows would run counter to our 'No Vinyl, That's Final' maxim that we try to use for all of our projects. Our research says it is worth the investment, and there is no way we could get near the Passive House standard without them. We will post some pictures in 10 weeks or so when they arrive.
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