window / windowsill

[piapiapiano]

In our house, the window frames have been fitted in between the internal and external sills. The wood is fine on the inside but, on the two windows we were able to see from the outside, the wood at the bottom of the frame is completely rotten.

A friend who's a carpenter told me that the frames should really be sitting on top of the external sills. Is this right? I confess I was hoping we'd just be able to repair the rotten wood and otherwise leave the windows alone.

 

[Feltwell]

Can you post up some pictures? That would help people to comment.

 

[Lime]

In general older houses had their wooden windows recessed and used an extended sill to take the water away.
Modern houses tend to have wooden windows almost flush with the external wall surface.

 

[piapiapiano]

I'll take a few pictures when I'm up there this afternoon.

I had no idea windows were so complicated!

 

[Flyfisher]

If the window frame does not sit on top of the sill the I suspect there's a risk of water getting between the frame and the sill and percolating down into the wall. But, of course, this will depend on the condition of the paintwork and/or other sealing between the frame and the sill. If there is a good seal then I can't see how water could get in between.

 

[Penners]

In our house, the window frames have been fitted in between the internal and external sills. ...Is this right?

Well, it rather depends on the age of the window, and how it's been fitted. Most recent window-frames have a groove cut into the bottom horizontal member, and the window sill has a tongue that fits into this groove.

Here's a (very) rough sketch of what I mean:



The internal sill is often fitted the same way, although tends to be less thick than the external one.

Of course,the above is not definitive - there are many different ways to fit windows.

 

[piapiapiano]

In which case, they really have been put in wrong. I've taken a few photographs.

We slid the sill out on Wednesday and found a couple of inches of wet cement mortar underneath it. It was so wet it was like it'd just been applied. The inside sill was just flush against that strip of white-painted wood. Here it is, without the inside sill:

Here's the outside, to show the rot:

And here's a close-up of the outside. You can just tell from the picture that the sill goes straight down where it meets the window frame. There's no tongue. My carpenter friend was able to stick his screwdriver vertically down through that little gap.

If I get new windowframes, will I have to get new sills too? Or can I just ask the windowframe guys to make sure the new ones go on top of the current external sills?

 

[biffvernon]

A friend who's a carpenter told me that the frames should really be sitting on top of the external sills. Is this right?

Yes, He's quite right.

 

[Flyfisher]

Is it possible that the window was once correctly installed but that the original sill has been replaced at some time?

Which leads me on to the question of how to correctly replace an external sill? Once it has been cut off from the window frame, what sort of joint is used to fix the new sill? A simple butt-joint would seem prone to precisely the sort of problem that PPP is dealing with.

 

[Me!]

Can you confirm what the external sill is made from please? It looks to me from the pictures that it is not wood, and that it could be stone, tile, concrete or similar? It also looks like you have a deep enough window recess that you could easily build new frames that move closer to the external face of the wall by the thickness of the new frame, so that it would sit on top of the existing external sill. However, I must stress that I have only ever had wooden sills myself, and I've no idea if this would be an appropriate course of action.

 

[piapiapiano]

The external sills are concrete, from what I can tell. We did think that we could put the new windows on top of the current sills, but then we wouldn't be able to use the old internal sills -- which are actually really nice, solid, big pieces of wood. Or, rather, we could use the old internal sills, but only if we didn't insulate or render the internal walls!

Also, the external sills are in a horrible state. How much hassle/expense would it be to get them out (bearing in mind that all the internal and external cement render is coming off the walls, and the windows will have to come out anyway) and replace?

 

[Penners]

Ah, if the external sills are concrete, then that's a horse of a different kettle of fish.

As I said above, there are many ways that windows are installed. The example I gave assumed that your external sill was wood, and that your window was relatively modern.

As your sill is concrete, I can't really see any reason why a window frame can't be made to rest on top of it - provided you ensure that there's a thorough seal between the sill and the bottom of the window-frame. If that would make it impossible to re-use the internal sills (I didn't quite understand that point) then I really don't think it's worth compromising the whole thing for the sake of a bit of wood.

 

[middi]

Remove the existing rotten window, repair, recast or have purpose made sills in stone. ( size of pockets determines choise).

Any of the above must have at least a 9 degree external slope. A new wooden window (is wooden sill cannot be repaired) with an appropriate external (standard) wooden sill can then be positioned level on the restructered ( and sloping) masonary type cill .An internal window ledge can then be fitted and all window to masonary gaps well sealed.

Properly looked after this will see your great grand children out before the window rots again.