Sealing UPVC windows?

13 Jul 2005
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United Kingdom
I'm just about to remove and re-fit two UPVC windows that are leaking. I want to make sure I re-fit these correctly - specifically sealing.

From the information I can find it seems that the sill should be screwed to the ledge (heads of screws on the back of the sill) - is that right? How do I make sure that water doesnt run down these screws, through the screw holes into the inside of the ledge and drip out of the ends to cause wet spots in the corner of my room (as is currently the case)?

I believe there should be silicone between the upstand of the sill and the back of the window?

I believe there should also be silicone at the ends of the sill/window as shown in my sketch. This wasn't added on my existing windows, I think this may be why I got damp patches at the bottom corners of the window inside the room?

Finally, silicone between frame and wall (also between sill and wall) as shown in my drawing.

Does this sound sensible or totally wrong?

Wall is brick cavity wall. Window is placed with back of sill flush with back of outer leaf brickwork. Cavity is closed off with plastic cavity closer.

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The drainage channels on the window frames exit from the lower front of the window frame; this then drains onto the top surface of the external drainage cill. You should have no water anywhere near the rear lip of the cill.

It sounds like your existing windows do not have drainage cut in them, hence the leak. Either that or your lintel is not getting rid of the water properly. Either way you do not want to silicone between the cill and the window, this could cause problems with the drainage.

After this you should fill any gaps around the frames with foam to stop any air leakage around the frame. Then silicone externally, looks better with brown silicone.

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