Cold Stone walls

[pattiw1950]

Having set the ball rolling about the Drimaster, another question. Obviously one of the problems we have is the fact that the walls are stone, the cottage faces north and is at the top of a hill and exposed to the elements, hence the walls are very cold so as the warm air hits............. condensation. Maybe this is a dumb question but you seem to be the experts. Is there any way to warm those walls up?

 

[Gervase]

Oh blimey, there's a can of worms stirred up!
You'll get all sorts of theories crawling out of the woodwork on this one.

Here's a couple of mine...

How thick are the walls and what are they made of? There's a school of thought that argues that if you've got a thick, rubble-cored wall, once you've got the inside dry and heated up to a certain point, the thermal mass will retain the heat. But if you've got the elements howling against the outside to the point where the water is saturating the core, then that's not so good.
So then you're looking at a roughcast render ('harling' to those north of the border) to keep the worst of the water at bay.

But then there's the school of thought that looks at tackling the inside. that means that exposed stonework is out. It has to be covered with something. Three coats of hair lime plaster will provide a degree of insulation which may well solve your problem.
If notm, then you're looking at battening the walls either using laths before plastering or using wood panelling so as to give an air space between the stone and the inner wall.

Most modern architects and BCOs, when addressing the conversion of stone barns and outbuildings to accommodation, will specify such an air gap, counterbattened with insulation inside. Unfortunately most architects these days will specify a multifoil, about which BCOs (and others of us) are dubious.

Whichever path you take, once the inner surface is no longer icy, a lot of your condensation issues will go.

 

[pattiw1950]

Thank you for that. The walls are just over two feet thick and are made from Cornish stone. I don't know about rubble-cored. The outside has been rendered and painted with masonry paint. We suspect that there is probably wetness trapped in the rendering. There is no exposed stonework inside. Somebody did a renovation job on this cottage about 6 years ago but we can't find out any of the details.

Do you think that stripping the rendering off the outside and taking it back to the stone would be a good idea and how big/expensive a job would that be? It's a 3 bed end terrace late Victorian so not a big house.

The hair-lime plaster suggestion - presumably then the old plaster would have to be taken off etc etc

 

[NT]

In short, insulation can be applied to the interior or the exterior.

NT

 

[Demelza]

So how would you insulate the exterior? Lime plaster too? You have probably guessed I am a complete novice so excuse the questions if they seem a bit dumb.

 

[Gervase]

I'd be tempted to take off the cement render and re-render the exterior with a lime-based render. Have a word with your local conservation officer to see what vernacular renders were used in your part of the world - in the west of the UK some form of roughcast or harling was pretty commonplace.
I would be tempted to do that first - you can take off the render now and starting putting the lime render on when the last risk of sharp frosts has gone - March usually.
If the place has been 'renovated' rather than restored, the interior has probably been rendered in cement and skimmed with gypsum plaster, which will make the walls feel cold, encourage condensation and trap moisture within the walls so, again, this is best removed and replaced with lime plaster.
However, you may want to defer the replacement treatment until you see how effective the external render has been, as that will tell you whether or not you need to go down the batten-and-air-space route or simply plaster onto the stone (using lime plaster).

 

[Nemesis]

And check that the walls are indeed not already the original lime and hair before removing it.

 

[Johneds]

Assuming your walls are granite, I wouldn't worry too much about the normal problems associated with external render. Water can't penetrate granite and the amount of water penetration through the joints will be minimal at two feet thick.

If I were you I would consider internal insulation. The batten method is good but you could also look at a thermal laminate plasterboard. (see link below) I have specified these many times in refurbishment projects of damp buildings and they really do transform a place.

External insulation is also an option but most systems are quite thick and I think they can spoil the traditional look of a building.

In terms of thermal response of each; external insulation means longer heat up times but the house stays warm longer. Internal insulation means the house will warm up very quickly but it will also cool down quicker.

http://www.lafargeplasterboard.co.uk/products/concepts/thermal1.htm

 

[pattiw1950]

The walls are not granite but Cornish stone, which I believe is quite porous. They've been rendered with cement and yes thw cottage was renovated rather than restored so I'm sure you are right about the plaster. At the moment the condensation seems to be under control and I expect we'll wait until the spring to decide about the outside. Maybe when we've got a bit more money!

 

[wyseass]

Is the batten method the same as dry-lining? I don't understand why the room would get colder quicker if it insulated internally? Surely it doesn't matter where the insulation is, the object of the exercise is the same - to keep the heat in and the cold out.

 

[MdB]

Is the batten method the same as dry-lining? I don't understand why the room would get colder quicker if it insulated internally? Surely it doesn't matter where the insulation is, the object of the exercise is the same - to keep the heat in and the cold out.

The stone wall will have a large thermal mass which means that it takes a lot of energy movement into or out of it to heat it up or cool it down.

If you have the insulation on the outside of the wall then when you heat the room you have to heat the wall as well. This means it will take a long time to heat the room but once it is heated it will stay warm for a long time once the heat source is removed.

If you have the insulation on the inside of the wall then you won't be heating the wall up so the room will heat up / cool down quicker.

The advantage of insulation on the outside is that it will keep the room warmer at night and cooler during the day. The advantage of insulation on the inside is there is less likelihood of the inside wall surface being cooler than the room temperature. This is when condensation forms.

Also note that if your wall is wet through damp then it will conduct heat a lot better than if where dry. I'm drying out my Cornish stone wall for exactly this reason (amongst others).

 

[wyseass]

What about 18 inch thick solid brick walls?