What’s the point of external window sills?

Aesthetics only or water management?

If water management, why; where there isn’t a window the wall gets wet when it rains.

easier to fix and seal inside a recess than flush. which leaves you with a sill.

I don’t think I have ever seen a question so easily and quickly answered on stw.

Being fixed in a recess also protects the whole window, extending its service life.
A window cill is also easier to replace, again meaning a cill can be replaced not just a whole window. This is for timber Windows.

The cill also makes it easier to keep water away from the bottom of the window opening – otherwise it would be harder to keep water out of the window/opening interface.

Thanks. Is this a timber windows thing. these days the bulk of windows fitted are not deteriorated by water as they’re plastic.

Also The opening interface is usually a reasonable margin above the sill though by the nature of the frame that holds the sash/opener

I never quite know if it’s cill or sill.

so students have somewhere to put their milk.

Whatever it is made of stone/wood/uPVC you need an overhang with a drip.

never quite know if it’s cill or sill.

It’s both, just to add to the confusion.

Otherwise you’d just see the ugly mess of foam left by the cowboys that fitted the window.
You can make a sill from concrete if you don’t want wood or plastic. Needs to slope out and preferably extend away from the wall so the drips don’t run back in. Some of our windows are mounted onto old concrete sills.

so students have somewhere to put their milk.

This is why they are often steeply sloped on public buildings and workplaces. Is the architect working with the fascist window sill police.

It also stops the windows being so manky having them recessed.

Water is tenacious it clings to edges and will flow through cracks you can’t see especially with a nice gust behind it. By recessing them the sealing only has to resist a fraction of the exposure to these things. Remember there are two seals, the opening mechanism and the one that connect the frame to the structure of the building.

It’s both, just to add to the confusion.

Both? At the same time? but in which order? Csill or Scill?

It’s both, just to add to the confusion.

Csill?

Also The opening interface is usually a reasonable margin above the sill though by the nature of the frame that holds the sash/opener

You’re missing the point – the opening is the physical hole in the building that the window fits into.

Without a cill [sill] water runs down the window and straight over the joint between the bottom of the window frame and the hole it fits into – this would eventually leak.
The cill keeps water away from this part of the hole/opening.

Ah, so if the sill is too short by a cm or so and the gap made up with mortar what might that mean- problems?

I don’t think I have ever seen a question so easily and quickly answered on stw.

It wouldn’t be STW if someone doesn’t come along and disagree with no evidence though

Psyll?

Ah, so if the sill is too short by a cm or so and the gap made up with mortar what might that mean- problems?

Probably not.
Pour some water down the glass and see where the water goes. Hopefully it will go across the cill and then drip off clear of the wall – if it runs along the bottom of the cill back towards the house and get to the mortar before dripping off then that’s a bit less good.

Ah, so if the sill is too short by a cm or so and the gap made up with mortar what might that mean- problems?

Yes. Sill (cill?) Needs to slope outwards and project a centimetre or two out from the wall. Easiest but ugly fix bodge is to put a thin plastic one one top.

Water is tenacious it clings to edges and will flow through cracks you can’t see especially with a nice gust behind it.

There’s medication for that.

Is this just a blatant attempt to get thread of the week?

But when the wind is blowing, rain hits the mortar elsewhere on the wall.

Is the point the that other mortar / brick is continuous and static, whereas the window is a flexible item that expands/contacts with temperatures and so the sealing around it less good?

You’ll be having a pop at doorsteps next.

No doorstep greater than 15mm allowed in UK new build now.

It’s the nanny state gone mad.

When I were a kid we had massive great doorsteps. Never did us any harm.

I prefer cill, not that it makes much difference.

But when the wind is blowing, rain hits the mortar elsewhere on the wall.

Is the point the that other mortar / brick is continuous and static, whereas the window is a flexible item that expands/contacts with temperatures and so the sealing around it less good?

Not flexible so much as the rest of the wall is sealed by mortar and any other supplementary coating, whereas the window is set into a hole in the wall, so requires a seal all the way round to prevent water ingress, but without a cill water would run down both the wall and the window, and collect along the bottom of the frame, so encouraging damp and leaking if the seal isn’t perfect, hence having a cill to encourage water to run off away from the wall. There should also be a small outward lip on the wall above the window, or else a small cill, also to encourage water to drip away from the window. I saw exactly this problem on a Grand Designs house, with larch cladding, where allowance hadn’t been made for a small angled timber lip above the windows, and it proved very problematic, they had to cobble a fix which actually looked ok, and solved the water leaking problem.

Cats,cats insisted that all windows should have inside and outside sitting areas.

No doorstep greater than 15mm allowed in UK new build now.

It’s the nanny state gone mad.

When I were a kid we had massive great doorsteps. Never did us any harm.

😁 As you get older you know is is just common sense as it it is easier to wheel your bike into the house.

Ask a silly (cilly?) question.

No doorstep greater than 15mm allowed in UK new build now.

The hilarity comes when you realise we still build flats….. With many stairs to the door.

kayak23
Full Member
You’ll be having a pop at doorsteps next.

First they came for the window sills…