UPVC Window Drain

Am 24.09.2025 um 10:06 schrieb RJH:

This makes me assume it is the latter. But i really don't know for sure,

I'd concur with that - cill profiles you buy typically are solid without a path for water to run through them:

Theo

Thanks both - seems therefore to be the bit between the glass and window frames. Good.

Um - isn't a drip groove a characteristic of an overhanging cill? I can't see a way for water to percolate underneath if I manage a decent seal between the stone cill and the window's UPVC cill.

Not sure TBH . . . it just looks rubbish as it is.

I suppose I could pour water into the mid-bar drain holes accessible when the top bit is opened, and see where it pours out. Hadn't thought about that, thanks. The risk being there's a blockage somewhere and the water goes elsewhere.

Or, take a glass out. Which I'll have to do at some point as the unit's blown. All 4 DG units have now failed on these 2 windows because, as far as I can tell, the installers used the wrong type of packer.

Along with failing to seal around the frame, overtightening the frames to the wall, and failing to fit trim pieces. They were at least measured correctly and sit reasonably square.

I cannot see a problem with sealing between the UPVC cill and the stone cill other than it is going to be a large seal and probably look unsightly. Using some UPVC trimming strips might make the sealing neater.

I mean that if water runs over the top of the plastic cill, it'll drip down onto the stone and run away. If you slobber silicone between the plastic and the stone like you were sealing a bath, then eventually when the silicone cracks (due to UV and thermal cycling) water can potentially wick behind it and become trapped. If you push the silicone back so that the drip edge is maintained then the water will drip off and not touch the silicone.

Theo

There should be a cap on the cill.

When I fitted some cheap DG windows 12 years ago, there were slots milled into the bottom rail, towards the front of the frame and lateral plastic 'beads' directed any water that leaked past the outer seals into these slots and then out into that horintal gap twixt cill and frame.

If you take a DG unit out (quite easy) you should see those drainage slots inside the frame and under the front pane of glass.

The ugly gap at the end of the cill should have been fitted with a moulding specifically for that purpose. The cills that were supplied with my DIY DG windows had plastic inserts that clipped into the ends of the cill which were supplied 6 inches too long and intended to be cut to the length required, either to the same width of the window frame or projecting 30mm either side and built into the brickwork, as the original timber Boulton&Paul windows were.

Ah gotcha, thanks.

Thanks to you Rob for raisng this subject. I'm no help at all to you, but your queston prpmted me to do some googling, and I now know a lot more about DG windows: principally, that there are lots of different kinds; secondly that there are real holes in them!

I was going to google anyway because I made a horrific discovery in our own kitchen windows just before I saw your thread here! We have window feeders for the birds on our kitchen windows (the type that sucker on to the glass, holding a little tray). We very rarely open these windows, but the other day I wanted to let a bit of air in, opened one, and noticed what looked like seeds littering the inside 'gutters' of the frame. Went outside to open the window wider: it wasn't seeds it was 7 kinds of black s**t from woodlce, slugs, and god knows what. It coated the whole of the lower edges including the "gutter" (the profile of these DG windows is _incredible_!). There was even a 2" slug sitting halfway up *inside* the frame! It was then that I discovered the vents/drains (who knew?!), which probably gave these creatures easy access (??? I've no idea how these vents work: I naievly thought the units are sealed unless you open the window. Terrible job to clean these parts of the winodw, but I've done it now, and have moved the feeders to the part of the window which does not open (but maybe that has vents too!

I found two vids which I'll pass on here: (1) How to keep your vents clean (who knew!?).

AJ

Decided to take the glass out* and replace it with new (went for E glass**), as the original had blown.

While at it I tested the drain. It is indeed between the cill and the subframe, and not the stone cill.

Thanks for all the suggestions.

• and nothing like as simple as the online video guides seems to suggest. The glazing strips quite rigid and firmly fixed. The special tool I've got had no effect. Took a hammer and a slender scraper to get them to budge. But once the first one out the rest are easy; a quick clean and wipe with silcone and it's a 10 minute job.

** About a 50% premium for a 0.9m2 pane (£60/£90). We shall see.

Figuring out which corner to start in, and which way around to proceed, then remembering what order to refit in reverse, and yes I found a nice thin clean scraper works well, I don't have a special tool.