How good are window rubber seals?

[nebjamin]

Hi all,

Bit of an odd one this one.

I had external insulation applied earlier this year. This meant that my windows needed over-sills. Trouble is, the windows drain onto the sill via concealed drainage channels and the oversills block the drainage channel.

I have had my window company fit 1mm aluminium oversills (instead of the 3mm ones the insulation co fitted), but the fit in the drainage slot along the bottom of the window is still tight and even with a good dose of CT-1 to seal the sill any water poured into the drainage slots through the frame runs to the edge of the original sill and into the insulation.

Basically, it's looking increasingly impossible to retrofit oversills and keep the drainage channels clear. I have spent well over £1000 on new sills and labour to fit them to try and rectify this problem and am running out of options.

Therefore the question is.. how good are the rubber seals around the edge of modern windows, and what is the likelihood of water getting past the seals and into the frame anyway? The windows are all new within the last 2 years and there certainly hasn't been any water get past them yet (I can see this because there's a layer of dust in there from all the building work!)

I am inclined to just seal up the drainage channel completely and keep an eye on the seals between the glass and the frame. If, say in 10 years they have perished or shrunk I could run some black sealant along the bottom of the glass to ensure no water gets in.

Running out of options..

Thanks,
Ben

 

[Gazman16]

I have always though this was going to cause problems and am supprized we haven't had more people on here asking about it.

Assuming the 1mm overcill is well stuck down wouldn't a little blob of sealant in the 2 corners do the job? The water may still run to the corners and just pool a little until it can run over the cill.

The drainage holes are also there to allow ventilation around the double glazed unit, Its not just about the rubber seals stopping water getting in. Humid air can still build up in there and if it cant get out it will cause premature failure of the glass seals (misted up units).

 

[AronSearle]

Windows are not really my thing, but I've heard of so many failures of direct rendar allowing water in around windows on new builds, I am only suprised we have not heard of much more issue for retrofits, which is even more difficult to seal.

If you use sealants to fix the problem, inspect them yearly, certinaly don't expect them to last 10 years.