Window Reveals

snow white

Ive just built a house and had a problem with a leaky window and a friend builder says the window is on the outer leaf and should be just be off centre in the cavity leaf...
I ordered the granite cills which look like they werent the extra wide ones and the window crowd said they just fit the windows to the cills...

Can someone tell me the correct detail for a window and the reveal of a window where there is a 200mm stone face to front of house also...

Ive seen on the internet that one house has the stone thickness of 200mm then 100mm of plaster then the window??

Im lost??

any help would be great?

Slig

Generally windows are positioned so that the outside face of the window frame is level with the inside face of the outer leaf of blockwork. The DPCs for this method are laid out in a specific manner and you have a 100mm(+render depth) plastered reveal on the outside.

By adding the stone to the outside but keeping this arrangement you will still have a 100mm(+render depth) plastered reveal followed by your stone cladding. To make this a nicer detail many people move the outside face of the window frame so that it is level with the outside face of the external leaf of blockwork. This ,however, requires the DPCs to be positioned differently and if your window frame isnt 100mm thick leaves a cold bridge around the reveal.

The position of the windows is determinded by the position of the DPCs not the cill. If they are not correct then the window will leak. Get them checked out by whoever is signing off your build.

mickdw

You have to assume in the general case that the inner leaf of blockwork in dry, the outer leaf wet and the stonework wet. This is the case except for special details which judging by your problem doesnt apply here.
The vertical dpc at the window is fitted tight against the inner side of the outer leaf. everything inside that point is dry and everything outside it is wet so the outer part of the windoww frame needs to be against the inner of the dpc.
With the stone work, it is best not to attempt to alter this arrangement as the block behind the stone is still a wet throughout. So there are 2 options to finish around the window in this case. Firstly the window must be setback 100mm + thickness of stone from finished wall surface, i.e tight behind the dpc. Get this right. Then you can finish the reveal by plastering the blockwork section or imo the proper detail is to stop the blockwork outer leaf 100mm short approx(this means the blockwork opening with 200 mm wider on the outside leaf than inner). The stone can then return back to the window and the plastered section can be cancelled out.
Now this means you have stonework meeting the window frame which doesnt give a seal like the plaster does. I would suggest sealing the DPC to the window frame thereby ensuring a waterproof detail and also then a mastic joint between the stone and the dpc to prevent wind/water blowing into the cavity although in theory, this should not give you a problem as it would be on the wet side but neccessary as the stonework with be irregular and there will possibly be large holes where it meets the frame/dpc
I will attach a detail if I get a chance

donal1981

Hi MickDW & Slig
Do you have a good drawing\detail of the window positioned in the outer leaf?

I am confused about the dpc?

I had planned to put my window in the cavity "as normal", however I ordered 15" cills - when the blocklayer went to install them we realised that they are too short to facilitate the window be placed in the cavity.

I rang the guy that sold me the stone,he said the 15" cills should be fine but i will be positioning them so that the window is in the outer leaf.

I am very unsure whether its wise to go with his advise or not. Hence i am hoping that you guys might have the knowledge that can help!

Thank you