Fitting Windows Behind Check Reveals - Sealant Options?

Not fitted windows before, but have some to do in the next few weeks. These are aluminium windows going in a mix of lead covered dormer and cedral clad wooden framing.

In my head I was going to use silicone around the opening as the windows go in for the frame face to but up to, then get up my scaffold to seal again from the outside with more silicone. But then I figured I should find out how it's done properly, did some Googling and came across EPDM rubber tape seals.

I've not really found a definitive answer as most of the search results are for fitting in the reveal rather than behind the reveal.

So, hows it done properly? If I use a tape seal, can I fit these to the check reveal before the window goes in and avoid having to setup my scaffold to seal these from the outside afterwards? If so what's the best tapes to use?

Thanks!

compriband tape could be a solution, I don't know how much time you get before it expands

http://www.compriband-tape.co.uk/

https://www.affixit.co.uk/expanding-foam-tape-compriband-alternative.html

Yeah, that was the one I'd seen, but also saw there are a few different profiles available. There's one with a D shape at the end which looks like it might fill the reveal corner/frame interface bit quite nicely.

I won't need much time to fit the windows once the tape is on as I'll be able to do all the prep first, but I guess I should drop that tape name into a YouTube search.....

Thanks

Had a look at a few videos, the bit I'm not sure about is that those tapes are designed to expand to fill a gap. With my windows behind a reveal, they will fit up tight to the inner reveal, which is well formed in timber, so will not let the tape expand in any meaningful way.

I guess it would work, certainly it should provide a better seal than the normal use, but I wonder if there something designed for my use that might be better.

paulrockliffe said:

that those tapes are designed to expand to fill a gap. With my windows behind a reveal, they will fit up tight to the inner reveal, which is well formed in timber, so will not let the tape expand in any meaningful way

Click to expand...

If you were going to use silicon you would be better to leave a gap so there would be a decent size bead all the way around, so it amounts to the same thing really.

Bear in mind a theoretical tight fit in reality means variable gaps as the timber stud work won't be perfectly flush nor will it be flat.

If you were to silicone a tight joint then the silicon bead would have to be on the surface and vulnerable to weathering.

For a dormer, I think I'd be wanting to trim the outside as well as sealing.

Are you sitting the window on a lead tray?

Dormers can experience high wind pressure, so rain will work its way into any gap.

Thanks that's helpful, the only bit I'd take issue with is that I built the dormer and the reveals knowing I'd be fitting the windows and dealing with any leaks, so they are perfectly flush and dead flat

The lead is wrapped into the reveal, so the sill will be sat onto the lead, the tray was properly welded in the corners too. The manufacturer says mortar or silicone bed for the sill, so I'll do that then any water that gets in and runs down will be directed back out again.

The dormer isn't in a particular exposed position, it's away from the prevailing wind and is shielded by a large extension to one side as well. It's been open to the elements with the hole filled with ply initially and then some insulation boards for the last few months and has stayed dry other than a couple of occasions.

I'm leaning towards fitting the foam tape then seeing how it goes. The inside isn't going to be plastered for a few months and it is the summer so I'll probably have a few opportunities to check it for leaks before it's covered inside. It's fairly easy to seal it or add trim alter if it's necessary.