High Performance Windows

One of the things I am most excited about in our house are the windows. We have a lot of windows in the house, 25 to be exact. And they are not terribly small. Even before knowing anything about energy efficient building, I’d always loved homes with large expansive windows overlooking a beautiful view. However, when building an extremely energy efficient home, the placement, size, glazing, window to floor ratio, and type of window matter a lot.

First, and perhaps most important, is which direction your windows should face. Obviously in the northern hemisphere, the sun is in the south. Therefore, the majority of your windows should face south and be able to take in the sunlight through the winter months when the sun is lower in the sky to provide some passive heating. Conveniently the sun is higher in the sky in the summer, so as long as you have properly sized overhangs or shading in the summer then you can prevent overheating. Recently we were in a neighbour’s house that was not designed with energy efficiency in mind. They have large south windows that are completely exposed, as well as some larger east and west facing. Even though they would (theoretically) have a great view, they had the interior blinds drawn on almost all of the windows!  Interior blinds and shades do very little to prevent overheating as the light/heat has already entered the space and will simply heat the blinds and radiate inside anyway.

For us, we maximized our southern exposure (but not too much as you can still overheat in the winter – even at minus 40° Celsius). And minimized our northern, eastern and western windows. Fortunately for us our best view is to the south and east. We do have a couple large windows on the east side of the house to take advantage of the river valley and our unobstructed view of the sunrise (to not put windows there would be foolish). We would have liked to have put more windows on the east, but in order to do so that would require shutters on the exterior, thus obstructing the view anyway. Shutters are really the only way to “shade” light from the east and west as the sun is too low in the sky throughout the year (at sunrise and sunset) to actually “shade” it. As for the north we don’t have much of a view, and so only have two windows. One in a bedroom for ventilation and fire safety and the other in the hall for ventilation. Northern windows really don’t provide any benefit in energy efficiency and are actually an energy penalty.

As for glazings, these are really amazing and can help with heat gain or blocking unwanted heat.The glazing does not at all block the view. I think of it like sunscreen. On the east and west windows, you want more sunscreen because you don’t want to overheat. On the south you want minimal sunscreen because you want that good passive heating in the winter (as long as you account for passive shading in the summer).

Ok so what type of windows do you buy? Wood, PVC or fiberglass? We had really hoped that we would be able to afford fiberglass windows. These are simply the best for energy efficiency, durability and quality. The frames themselves are made of 60% glass (fiber-glass) and so they move with the expansion and contraction from the heat and cold of the windows. Consider -40°Celsius outside and +20°Celsius inside. That is a 60° change that occurs through about a one inch space. PVC and wood will flex and bend at a different rate then the glass, leading to more air leakage, reduced air seal, and eventual failure of the window over time. Fiberglass however does not have the same issues. Duxton Windows has some excellent information on their website.

Now that we had an idea of what we wanted, we needed to determine which supplier to go with. We priced out Duxton (fiberglass), Accurate Dorwin (fiberglass) and Plygem (PVC/wood). We did not consider any of the crazy German imported windows. Shockingly, people actually do this (this is where the economics of Passive House and extreme energy efficiency clash with reality and sustainability, as I’ve written about before). I was actually talking to a house designer the other day who was raving about some German windows they’d started to import. Indeed they are impressive windows – but they are coming from fricking Germany! My thought when building a “sustainable” home is that we should be really considering if we are spending our money wisely or if it could have a better effect elsewhere (for example, spending $15,000 more on windows to get a marginal energy improvement versus $15,000 in solar panels). AND if you are importing your high performance windows from 4000 miles away and shipping them on a cargo ship across the ocean… well… is that sustainable?!

Anyways, I knew that the fiberglass windows would be more expensive than wood/PVC – but how much more was the question? When we received the quotes back I was pleased to see that the fiberglass windows came in only 20% more expensive then PVC. For the added efficiency, durability, warranty and, not to mention the larger viewing area of the window (fiberglass is stronger therefore can have a smaller frame and more glass) it was a no-brainer to go with fiberglass. We ended up choosing Duxton over Accurate Dorwin due simply to the fact that our designer had recommended them. The price difference between the two companies was marginal.

In designing the house and choosing the windows I tend to think about what Christopher Alexander of the Pattern Language says: “light on two sides of every room.” I loved reading this book because it was all about aesthetics. Written in the 1960s, it did not give a crap about energy efficiency. It was a nice reality check against all of the energy efficient dogma that in some cases can really get out of control. You still need a home that you actually want to spend time in.