Because they have always leaked when raining and today I sprayed a hose on them for a good 20 mins with someone inside watching for leaks. Definitly started leaking when it was sprayed - just in a few different points on the tops and bottoms. Nothing on the sides.
On this point - I know that Keylight roof windows have an expanding foam strip which seals between window frame and roof rafters. What is usually done on velus windows? Presumably if nothing is added then this is likely to drip on plasterboard. Some expanding foam?
