Weather seal on windows- flashing tape?

[Crofter]

My windows are now all installed and low expansion foam used around the perimeters. Following instructions that I was given by the supplier, I have not filled the whole of the depth of the window frame but have left a small gap as viewed from the outside. I now need to create a weather seal but at the same time not create a 'vapour sandwich'.

If I just use conventional sealant from a gun, this will almost certainly fill the whole remaining gap and there will be no drain space left. On a very narrow gap I might get a bead of sealant to adhere to the window and ajoining wall, but on the wider gaps this isn't going to happen,

 

So I am wondering whether I could use some form of tape instead? I see tape being sold as a self adhesive flashing and this appears to be appropriate, according to the blurb.

The front of the window frames is in line with the front edge of the house frame, so the tape would simply bridge the gap between them, leaving a drain cavity behind (and a suitable drain point located somewhere along the bottom edge of the window).

The tape would then be hidden behind the cladding and window reveals, which would provide an additional layer of weather protection.

 

Attached is a cross section as viewed from above, attempting to show what I'm talking about...

[ProDave]

Normally the cladding (timber in your case) would go on after the windows are in, and that would bridge the gap you are talking about.

 

 

Yours are Rationel aren't they? any moisture that gets between the wood frame and the ali cladding can drain out of the bottom of the gap onto the cill.
 

[jamiehamy]

Compriband? We've used that on ours and fills the small space beautifully. Iirc, it's breathable too, but weatherproof. We used Tremco TP600. I'll try get some pics at the weekend. 

[Crofter]

The cladding does indeed go on after the windows are in, and yes that will cover the gap around the perimeter. I just wanted something else as a seal though. It's a pretty exposed site here.

I'll look up compriband, thanks Jamie.

[Stones]

How big a drainage channel do you have to leave and where ?  I would have thought the best place for the weather seal would be in the gap you have left - using sealant or compriband, then as Dave says, bridge the gap / cover the weather seal with your cladding.  This is what we have done, and IIRC think Dave has done as well.  We used sealant rather than compriband, because of the poor reputation of compriband up here.

 

[Alex C]

I was advised to not let my window installers fill that gap with silicone, as it can crack away over time. Instead I foamed flush with the front of the frame, trimming it off neatly with a knife  and then fitted Siga Wigluv tape, which is designed specifically for this type of job. the tape is expensive at about £1 a meter, but I think the £280 I spent and few days fitting was time and money well spent. My windows are set back into the reveals so potentially is more of an issue as water can sit under the cill and track under the window.

[Crofter]

@Alex C I do like the method you describe and it is pretty much what I had in mind myself.

The Wigluv stuff is pricey though- I'd want to do it in black, in case any ends up being visible, so that would be about £55 a roll- ouch.

I could do it using 'flashband' for less than half the cost, and it seems to be fairly tough stuff, much more easily available. Soudal do a version and I've had good experience with their products in the past.