Good windows are a very important part of a passive house, as all element of the building envelope are to perform at their best. And poorly insulated windows are cold surfaces in the room and will need some sort of heat source nearby to compensate for the “cold draft”. The Passive House Institute certifies so called “warm” windows that fulfill the requirements for the passive house standard, in Europe there are around 60 manufacturers on the market. Four criteria are important: triple glazing, a warm edge spacer, insulated frame and thermally correct installation in the wall.
One issue here in Canada is that these windows have to be imported from Europe, mostly from Austria, Germany or Ireland. And that certainly adds to the cost. So what is so different from typical North American windows? Once you have installed one or operated one you know. They are heavier, have more seals, typically they have a tilt and turn operating hardware and in closed position they are really air tight. They are the BMW of windows.
Well insulated windows are necessary to provide solar heat gain the winter, because remember the passive house doesn’t have a furnace…. that works especially well on cold and sunny days as we have them here in Ottawa quite often. This could be achieved with any window, but overall the window has to contribute to a positive energy balance – meaning the house gains more heat through the window than it looses.
So how well insulated are they? As a guideline the u-value of the window assembly has to be below 0.8 w/m2K, the equivalent of R7.