Help - problem with new window leaking (again)!

5 Dec 2021
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United Kingdom
Hi folks,

I'd appreciate your advice please. I've had some expensive aluminium windows installed - Alitherm 600 by Smart Systems.

One of the windows is a large dormer window with 4 panes. After it was installed it quickly became apparent that it was leaking. The installer took the panes and frame out to investigate.
The following issues were brought to my attention:

1. There was a mistake in the order/manufacturer that resulted in the window needing to be flipped round so that the drainage holes were at the top on the inside, and new drainage holes drilled by the installer. Apparently this was something to do with the glass needing to be fitted from the inside. I was assured this is not an issue.
2. The frame was a bit tight in the centre so the installer used a grinder to shave off about 5mm off the centre of the frame. As this is hidden I was assured this is not an issue.
3. The supplied cross sectional picture shows a large strip of foam insulation that sits in the space at the bottom of the frame and on the sill (ACET619 in the pic). This was not installed. I was assured this is not an issue.

Now to the leak:

1. The whole sill was full of water. There were no drain holes to drain water from the trough in the sill out under the lip.
2. The ends of the trough were not sealed with silicon sealant.

The installer drilled holes to drain the water from the trough in the sill and sealed up the ends with silicon. Window back in. Job done!

Of note, the 3.8m bit were the frame meets the sill is not sealed. The diagram doesn't say to seal it. The technical advisor from Smart systems said not to seal it. Apparently any water that comes in here will just drain away.

Also of note, the installer was of the opinion that the main source of water was not the 3.8m long metal on metal joint, but instead coming in at the corners of the seals. We caught about a litre of water over night before the first fix.

Anyway, window in. Plastering all done, including ceiling below. Then some rain. Now evidence that the leak is still there.

This window was very expensive. I feel uneasy about it being cut down to fit, with it being installed upside down and with new drain holes being drilled everywhere. I also feel uneasy about silicon sealant being used to prevent what is quite a significant leak.

I'm starting to think we need to start again and order a new window with the drainage in the correct place and all the foam inserts etc all in place. I don't want to be a d**k though if this is reasonable snagging. I'd very much appreciate your thoughts and suggestions.


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