Jackson DigneyDirector, Enduro Builders · Passive House Builder | Director, Enduro Builders

Window Design Matters - Energy Efficient Homes | Enduro Builders

8 Oct 2025 · 2 min

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2:12

The presenter explains how high‑performance glazing is a core pillar of Passive House construction, focusing on the use of double‑glazed uPVC windows and doors. These windows provide both thermal‑bridge‑free framing and superior insulation. He defines the two key glass performance metrics—U‑value (the inverse of R‑value, where lower values mean better insulation) and Solar Heat Gain Coefficient (SHGC, the proportion of solar energy transmitted). The talk emphasizes the need to balance these metrics: north‑facing windows may benefit from higher SHGC for winter heating, while shading can mitigate summer gain. He also notes that better U‑values increase cost and can lead to overheating if a house cannot shed heat at night, a particular concern in Australian climates. The overall message is to carefully select glazing that optimizes winter heat retention, summer heat rejection, cost, and thermal‑bridge avoidance.

Chapters

One of the pillars of a Passive House is high-performance glazing. In the case of this house, what we're using is double-glazed uPVC windows and doors. That also helps us tick 2 of the pillars of a Passive House: thermal bridge-free construction and high-performance glazing. The glass is double-glazed, which gives us the extra insulation that we need, and the frames are made out of uPVC, not a material that generates a thermal bridge. If you're thinking about your glass choices on your house, glass is measured via 2 different performance characteristics. The first one is the U-value, which is the thermal conductivity of the glass. So a U-value is basically the opposite of an R-value in walls and roofs. So as an R-value goes up, that means you've got more insulation. So U-values are the inverse of that. So as the U-value goes down, that means you've got insulation. The other measure that glass has is the solar heat gain coefficient, and essentially that's how much solar heat passes through the glass into the house. You actually have to balance those 2 against each other. For instance, on north-facing windows, you may want a higher solar heat gain coefficient so that in winter you get lots of heat coming into the house, And in summer you can counteract that with shading. You also want to consider the U-value of the glass because usually the better the U-value of the glass, the more money it costs. And sometimes you can have a problem where you have too much insulation and the house can't shed heat at night, particularly during summer in Australia. That's something that you really need to consider, balancing the ability to lose a bit of heat overnight in summer against the amount of heat loss in winter.