Are uPVC windows waterproof? Here's an honest, precise answer.
The uPVC material itself absorbs essentially no water — it can't swell or rot. But a *window* being weathertight depends on more than the material: the gaskets, the glazing seals, the drainage, and the fitting all have to be right.
So: the material is waterproof; the window is weathertight if it's built and fitted properly. That distinction matters, because a uPVC window fitted badly will still let water in — through the gaps, not the plastic.
The uPVC material absorbs essentially no water and can't rot or swell. But the window's weathertightness depends on gaskets, glazing seals, drainage, and fitting — the material being waterproof isn't enough on its own.
Through poor sealing or bad fitting, yes — not through the material. Frames also have drainage channels to shed any water that does get in.
Well-made, well-fitted ones don't. Leaks trace to sealing, drainage, or fitting rather than the material.
Related guides covering this topic from other angles — different products, applications, or contexts.
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