Damp Bay Window

[Downsey_95]

I haven't had one quite like yours, but I've had them with a strong timber frame, tile-hung or pebbledashed on the outside and L&P on the inside.

Easily improved by cleaning out and adding membrane, insulation and plasterboard, with extra sockets on the bay and mineral wool in the floor to block draughts. I like to pack mineral wool into the frame as it is easy to fill tightly with no gaps, blocking draughts, but the foam is a better insulated. You can lay an extra sheet onto the face.

But in your case I think a new timber box frame is needed, and I would use sheathing ply on the outside for extra strength and rigidity, and new brackets off the wall. IMO the old frame is poor and falling off.

If you can find a leadworker, they can probably make it more weathertight than you could do yourself.

I don't think your window contractor is up to it.

When you expose the timber, there is a chance you will find it is well made and just needs woodworm killer, new brackets and screws

But I doubt it.

Hi John,

Thank you for your help with this. Ideally I don't want to be touching the current framework as I believe from what I can see there is no movement and seems to be quite rigid - I don't want to disturb anything.

How would you suggest strengthening the current framework?

I think we're going to bull the celotex and for between the current framework, then put the membrane and new plasterboard. Would you suggest insulating the floor near the bay?

Thank you for your help!

 

[JohnD]

Pull off the plaster and render and you can see what you're doing.

You will need to take off some plaster from the inside wall to attach brackets and straps. It looks to me like it is falling off.

I can't visualise quite how to do it because you will be hanging the frame off the wall and also pulling it in towards the house. Some diagonal steel straps might do it. Roofing timbers are strapped down to walls to resist blowing away.

You can wrap the frame in roofers breathing membrane to throw rain off. It is cheap enough that you can do it while working, and again before you finish the outside. You want it to be weatherproof from the day you start to the day you finish.

 

[Downsey_95]

Pull off the plaster and render and you can see what you're doing.

You will need to take off some plaster from the inside wall to attach brackets and straps. It looks to me like it is falling off.

I can't visualise quite how to do it because you will be hanging the frame off the wall and also pulling it in towards the house. Some diagonal steel straps might do it. Roofing timbers are strapped down to walls to resist blowing away.

You can wrap the frame in roofers breathing membrane to throw rain off. It is cheap enough that you can do it while working, and again before you finish the outside. You want it to be weatherproof from the day you start to the day you finish.

Hi John,

We will be pulling all the plaster off so we can see the framework and take it from there. Probably re-strengthen the frame and add the celotex and make the wall deeper to enable a deeper window cill. Do we need to leave a gap behind the celotex?

I think we will end up getting outside re-rendered so will end up paying someone to do that. So then it's all renewed and moisture resistant

 

[JohnD]

Do we need to leave a gap behind the celotex?

No.

Wrapping the outside in roofers breathable membrane (modern replacement for felt) will keep rain out and allow vapour to escape. You will need detailing to keep rain out, especially on the top, and lead is the best permanent solution. The renderer will probably use a modern cement backing board that can be fixed to the frame. Rendering into a loose cracked old layer is likely to crack.

It's a good idea to have a vapour barrier (such as foil backed plasterboard) on the warm side, to prevent humidity from the room getting into the cavity, where it would condense in cold weather. Bays with a wooden frame like yours tend to be quite draughty so you can stuff any gaps with mineral wool to block draughts, but must keep them dry.

 

[Downsey_95]

Hi all - From taking more of the wall down the wooden frame looks solid but can see in some places the wood has started to rot. What would be the best sealer as will coat all the wood in this for durability before we insulate etc. Thanks