Is damp on the inside of the single brick deep wall under my first floor bay window actually from condensation?

[DaveAF]

Hello.

We have a first floor bay window that sits on a brick wall that is 1 brick deep with render on the outside. The render had a few vertical cracks which were repaired and the outside of the house was repainted a couple of years ago.

Please see the photos. 

In the middle of the bay window is a long radiator.

On the wall beneath the window cill there is damp on the left side where the cill touches the side wall and this damp continues across most of the bay under the cill. There is no dampness on the side walls above where the window cill touches them. 

There is also white mould on the wallpaper. Where wallpaper has been removed for photos the plaster is cracked and discoloured. 

Two questions - 

1. Could this dampness be due to condensation? 

2. Will replastering the wall then insulating it cure the problem? 

 

All thoughts welcome. 

David. 

Edited January 28, 2023 by DaveAF
Missing information.

[Radian]

Very likely just to be condensation. It's only to be expected on such a cold surface indoors. If you wanted to be sure you could tape a polythene sheet over the whole area (tape it very well so inside air can't get between the sheet and the wall). If water is coming in from outside it will be apparent on the wall side of the plastic, conversley if the wall stays dry but condensation appears on the room side of the sheet then it's coming from the atmosphere indoors.

[markc]

I would also say it’s condensation, no downward streaking to indicate leaking through window etc.

[DaveAF]

10 hours ago, Radian said:

Very likely just to be condensation. It's only to be expected on such a cold surface indoors. If you wanted to be sure you could tape a polythene sheet over the whole area (tape it very well so inside air can't get between the sheet and the wall). If water is coming in from outside it will be apparent on the wall side of the plastic, conversley if the wall stays dry but condensation appears on the room side of the sheet then it's coming from the atmosphere indoors.

Science! Wow. Thanks so much

[DaveAF]

10 hours ago, markc said:

I would also say it’s condensation, no downward streaking to indicate leaking through window etc.

Thanks.

I've literally spent hours in the front garden with binoculars in the rain scanning the windows trying to find the leaks. The neighbours must think I'm dotty. The possible condensation cause just struck me yesterday. 

So to make the single brick wall less cold would fitting insulated plasterboard be a way forward? Any thickness recommendations? 

[Radian]

The single brick wall between you and the great outdoors is a severe cold bridge. I expect there are others (like the top and sides of the window reveal). Insulating the obvious bit beneath the window will only get you so far as, at the moment, this is the area most attracting the water vapour in the air to condense. You might like to think of this area as a large dehumidifier with no running costs but also no water management. 'turn it off' by insulating the wall and the next coldest area will suddenly develop a damp problem. You need a more holistic solution.

 

Does the rest of the wall have a cavity and if so is it insulated? What about the roof at the top of the bay - it's not visible in the photo.

 

 

[DaveAF]

Yes I suspected that the problem might move on to the next coldest spot.

I've added 2 pictures.

One shows our 2 windows.

The second shows a neighbours bay roof which is similar but the picture is taken from higher up so that the roof itself is visible. 

 

The walls to the sides of the bay window are twice the thickness of the wall below it. I'm unsure if that means there's a cavity or not.

I'm uncertain if the property had cavity insulation put in before we bought it 15 years ago. 

 

The roof just above the bay window is flat and felted and from memory has, at most, 1 inch of white polystyrene foam sheet placed on the plasterboard. No vapour barrier on the plasterboard nor foam sheet. I guess that to add more would involve removing at least one section of the plasterboard ceiling?

 

My final questions are what thickness (and type) of insulated plasterboard would be required to make my bay window wall warmer and what thickness would insulate the roof better?

Could the same type work in both situations? 

Sorry thats 3 questions. 

Any thoughts are much appreciated. 

David