Do I insulate outside walls?

[Ian]

This may seem a silly question, but opinions seem to vary, so if I may have the benefit of your experiences?

The walls of my house are of traditional stone construction - inner and outer skin (some dressed stone outside)  with rubble in the middle, all held together with lime and mud. It's all built over vaulted caves, and the ground-level layer is hard stone (early DPC), so it seems fairly dry.

My simple plan was to build a false wall (metal rails etc) about 70mm out from all walls, with 50mm of rigid insulation behind, leaving a small airgap between it and the wall. However, having read some of the postings here, it seems this would just encourage dampness from the walls - instead, I should omit the insulation and let the walls breath. Or, go with Plan A, but put a breathing membrane (pare-vapour?) between the insulation and the stone.

Any advice, people?

Thanks

[Bugsy]

Good morning Ian,

We have the same walls which I have, as advised by a local builder, rendered with a lime/mortar mix. His advice (he has a very good reputation here) was to never seal the walls. Damp will always follow.

The stuff I used was called 'Tradifarge'.

Hope this helps.

Gary.

[Pierre ZFP]

Sounds to me like you could be wasting your money and potentially causing a future damp problem.  These walls are built like that for a reason.  They need to breathe and not be covered with modern materials.  If there is no damp or condensation at the mo' I'd leave it alone.  Why do you think you need to do this?  Is it because the wall feels cold to the touch?  They often will as the wall has great mass and good thermal contact with your hand will make the wall appear cold.  Can I suggest getting a thermometer and measuring the air and wall temperature.  I bet they're not very different in which case insulation aint gonna make a halfpenneth of difference

[raindog]

[quote user="Bugbear"]

Good morning Ian,

We have the same walls which I have, as advised by a local builder, rendered with a lime/mortar mix. His advice (he has a very good reputation here) was to never seal the walls. Damp will always follow.

The stuff I used was called 'Tradifarge'.

Hope this helps.

Gary.

[/quote]

I did the same thing at our place, left an air space, then built inner walls with 5cm red bricks and got them plastered. I only used placo for partitioning, never for inner walls.

[Nick Trollope]

It's all about dewpoints, innit? As I understand it, the dewpoint is the point (in space at a given temperature) that the water vapour becomes water. Normally, this occurs somewhere between the warm room and the cold outside - in the middle of an unclad wall. Not a problem if the wall can breathe. By insulating the inside of the wall, you risk moving the dewpoint into the gap behind the insulation, or worse still, on the back of the insulation. This will cause 'orrible problems..

My advice, based on experience, is not to insulate outside walls, but to ensure that you have plenty of ventilation to the space behind the placo. On a couple of occasions, I have insulated the top 1/2 of a wall (and ventilated) with no ill effects.

Or you could lime render it...

 

 

[Ian]

Thank you, everyone, for the advice.

I will follow it and leave an uninsulated space behind the placo, which should be better for the walls. It will also save me time and money, music to the ears of a Scotsman.