Condensation on walls/ceiling inside a bay window

[testsubject12]

Hi,

I have an interesting problem with a couple of possible solutions.

I live in a 1940s ex council property where quite a bit of insitu concrete moulding/pouring was utilised in the construction.

The problem I am seeing is associated with the dining room and one of these large slabs of concrete. There is an alcove where the room juts out by approximately 1m and this has a 1.5m run making up approx half the total wall run. The window in this alcove has a concrete lintel, but this has had a reinforced concrete slab poured around it to make up a flat roof (which extends as a porch to the side over the front door) and to bring it back inline with the second story. There isn't any form of external covering to the concrete.

As you would expect this slab gets very cold and so this invites condensation to form on the inside walls and ceiling within the alcove and allows mildue to flourish.

We have been through the route of dehumidifiers and opening the windows etc., but we decorate and then it returns because of the water.

As I see it we have 3 choices.

1) Convert the small flat roof to a pitched roof and insulate on top of the slab - I'm not 100% sure what's needed and would be quite expensive. (A few pointers would be good) + we already have planning to do this from when we had the extension done, just the builder was crap and couldn't get off the job quick enough once the main extension was done, so he could get on with his next job.

2) Insulate inside the room - issues with window and risk of just hiding the problem and might not work?

3) Add some kind of exterior coating and hope it goes away?

Anyway, any suggestions or pointers would be greatly appreciated.

Thanks

Paul

 

[pompeyal]

Hi Paul, I would personally go the pitched roof way, this would then cloak the problem you have and the house would look nicer for it. FInd a small jobbing builder to quote you, it will be more expensive than trying other methods but at least you will only have to do it properly once. it could even put a little more value on the house. Have a look at houses around where you live and see if anyone else has had it done, knock on there door and ask them questions about it, they may even recommend somebody.

 

[testsubject12]

Thanks pompeyal, that's what I was thinking anyway. I just don't have the cash spare at the moment to get someone in. I was going to attempt it myself as I have done quite a bit of DIY in my time.

Do you have any pointers on what is needed? Or what I should look out for?

I was thinking add a wallplate around the edge of the slab and then add the new pitch on from there. Is it ok to insulate directly on the concrete slab as I wouldn't like to try and remove the slab as it goes into he outside skin of bricks of the main house.

I definately think it will improve the look of the house. Which is why we have it on the planning consent for the extension.

Thanks again

Paul

 

[pompeyal]

You first will have to work out the quantities of materials required for the job.

Build the timber trusses onto the slab and maybe insulate using celutex RR insulation slab, just cut into sizes that will fit tightly between the timbers. The timber size will depend on the span but if the concrete slab is the size I think it may be then 110 x 50 should be adequate but please check. ensure correct fixing and bracing techniques are used, once this is done felt and batten the frame then tile over. chase out the render above the tiles and install a lead flashing. You will have to check on the weight lead is required. Fit the facier and gutter/down pipe and that should be it. I am not a builder so don't take this for gospel, check first and look on your plans for specifications set by your architect which drew up the plans for the extension, good luck Al.

 

[testsubject12]

Hi @pompeyal,

Thanks again for the reply, what you have described is pretty much what I thought was needed anyway, so I guess I'll have to have a proper measure up and then get myself to the builders merchant to sort it out.

I was a little unsure of "check on the weight lead is required" but I'm guessing that lead roll has a weight rating as well as a size?

Do you know if you always have to install/ add groundworks to connect to a soakaway for the rain water or is it ok to just direct the water away from the property?

Thanks

Paul

 

[pompeyal]

I was a little unsure of "check on the weight lead is required" but I'm guessing that lead roll has a weight rating as well as a size?

Do you know if you always have to install/ add groundworks to connect to a soakaway for the rain water or is it ok to just direct the water away from the property?

Yes, lead has a weight rating.

With respect to drainage you would have to find out from your local planning office, they should put you right.

Regards Al