Thermaboard/damp proofing solid granite walls

[locoloic]

Hi all,
I'm about to buy a house which has some very old sections, with walls as old as 1590. These are probably the best part of 900mm thick, granite walls.

There's a little damp on a couple of the corners of the property with these external walls, so I'm looking to find a decent solution for this, though I've been reading mixed opinions. I should note that the outside walls are all feature walls, so external thermal cladding isn't an option, and we can only look at internal solutions.

Here are the options I've heard so far:

1) Thermal board over the current plaster. The adhesive for the boards is added in a continuous line running a few inches from the edge of the boards, sealing the moisture from the outside. This eats into the room space somewhat.

2) Similar to the above, but removing the current plaster first, perhaps using metal batons to mount the boards. Thicker thermal board can be used for this, as it would eat less into the room space.

3) Special permeable plaster and paint that allows the moisture to leave the walls to be dissipated within the room.

What is everyone's opinion on this? I'd like to improve the thermal properties of the walls, so the thermal board sounds good, but to me, sealing in the moisture into the walls seems like a great way of creating a very serious mould and wet rot issue that you don't notice until it's really serious and widespread.

Thanks in advance for any advice!

 

[endecotp]

sealing in the moisture into the walls seems like a great way of creating a very serious mould and wet rot issue that you don't notice until it's really serious and widespread.

Correct.

Firstly you need to understand the cause of the damp. Is it condensation, or is it from outside?

Don't do anything in a hurry. I presume the building is listed; talk to the authorities and learn what you need permission for.

(I live in a building from 1643.)

 

[locoloic]

Thanks for the reply.
You raise an interesting point - the mold appears midway up the walls on the outer walls only, and also on the first floor. My suspicion is that is would be from condensation rather than ingress externally or from leaky drainage. The house has been leased out the past few years, and I don't think the tenants put much care into the house.

If it is indeed from condensation, wouldn't the thermal board approach be a workable solution? This would insulate the outer walls, bringing their temperature up, and reducing the amount of condensation.

I see there are some anti-condensation paints, but I can't see that being very effective on this sort of wall.

I think we're going to start by ripping off all the horrible damp wallpaper and seeing what's underneath, then taking a view from there. A coupel of radiators are leaking too, so I'll probably swap these out with larger units to heat the house more, and might also double up on the attic insulation. I expect a warmer house in general would help with damp.

The building isn't actually listed, which is a bit of a result.

 

[endecotp]

I'm surprised it's not listed; I thought almost everything from before 1700 was automatically listed unless it had been spectacularly ruined.
Are you relying on what the vendors have told you?

BTW, "isn't listed, which is a bit of a result" sounds like a red flag to me! Do you want to live in an old building or not? If you don't want to live in an old building, buy somewhere newer! I'm sure you'll be happier.

Improving the insulation of a portion of the wall/ceiling/floor will reduce the chance of condensation *on that portion*. But if there is moisture in the internal air and there are other cold surfaces, it will condense there instead. This is one reason why insulation needs to be everywhere; if there are small areas with worse-than-average insulation, they will suffer condensation.

 

[locoloic]

The property is in Jersey, and the local planning department can be rather erratic in their rulings, seemingly depending on how they feel that day. So, one listed property might be permitted to have double-glazing installed, whereas the next of a similar age and style will absolutely need to have the original wooden sash windows restored.

Also, some properties have been exempted from being listed, despite their ages. This could be down to the development of them (extensions), whether they're visible from public roads, other houses built in the area etc. This allows us to modernise, and do in in a style that is very sympathetic to the original traditional house, but not have to run it by the local planning authorities (and of course, cross their palms with silver each time).


Back to the damp, I absolutely agree. I'll look into insulating the entire property as much as possible.

 

[endecotp]

run it by the local planning authorities (and of course, cross their palms with silver each time).

You have to pay for listed building consent applications???