Clients (and their designers) who want high-performance buildings on a limited budget need to consider uPVC windows. Elsewhere, almost every Passive House on a budget will use uPVC joinery, typically white inside and out to maximise performance and minimise cost.
Note though that uPVC windows are also available with an aluminium cladding on the exterior face to allow a choice of colour and further UV protection.
The main argument against (besides aesthetics) is the fear that uPVC ‘won’t last’. How long is long enough is an interesting question, but I’m advised uPVC windows will last more than 30 years without maintenance. I’d expect the aluminium clad ones to last 40; again without maintenance and that is a big plus. I’ve seen uPVC windows in Plimmerton (near Wellington, coastal environment) that are in good shape still after 30 years.
Do note that not all uPVC windows are the same and many of the ones sold in New Zealand are not acceptable for Passive House builds as they are ‘modified for local conditions’ without a deep understanding of performance.
Also, the life span of exposed uPVC is determined by how much UV stabilizer is added (titanium dioxide usually). My lifespans noted above refer to good quality uPVC. Like anything else, you get what you pay for.
—20 April 2020