Renovating a stone walled house

[Carnmore]

The house is single storey and circa 100 years old with solid stone and lime mortar unplastered walls about 450mm thick.

It consists of just two existing external walls (40m2) , a party wall, an extension to be rebuilt at the back and a roof to be renovated (slates removed, timbers repaired where necessary, felted, new roof battens and reslated using original slates.

The finished floor has been poured - rigid insulation board and cement.

For insulating the external walls, my architect and builder are recommending installing a steel stud wall to create an air gap and then dry lining with insulated plasterboard.

I'm on a budget and the cheapest method is insulated plasterboard as described above which would cost about €1k. Despite this cost and advice, I'm concerned about the breathability of the walls.

I would also prefer to use non-toxic materials where possible.

Would Calsitherm or Gutex be a better option or is insulated plasterboard okay?

The cost of Calsitherm including a lime scratch coat would be circa €10k..

Thanks in advance for any advice re this or in general.

 

[Andy836]

What they're recommending seems fine.
If the walls use lime mortar/render then water should be pushed out of them. On the inside it will evaporate in the newly created air pocket (make sure there are vents installed for the air pocket or else the water could pool in there at the bottom).
Make sure the ground outside slopes away from the bottom of the external wall so to limit rising damp. If not then install a french drain around the perimeter.

I am not a builder but I have read a strange amount of stuff on damp and insulating masonry buildings.

 

[Carnmore]

On the inside it will evaporate in the newly created air pocket (make sure there are vents installed for the air pocket or else the water could pool in there at the bottom).

Make sure the ground outside slopes away from the bottom of the external wall so to limit rising damp. If not then install a french drain around the perimeter.

Thank you. Where would the air pocket be vented to?

 

[fear_gall]

I have a similar rubble stone wall house with lime mortar. The house was renovated in the early 1980s and a timber stud and plaster board system was put against the outside walls. The outside was wet dashed with cement(non breathable). It worked for 30 plus years. We are now renovating it and putting breathable external insulation on and have removed the timber stud and plaster board internally and have replaced it with a hemp-lime plaster. It is excellent at smoothing out the variations in the internal walls and is a lot cheaper than lime alone. We have done 200 sq metres of it. There is a Facebook called cottageology- Irish cottage renovation and appreciation where a lot of different people have shared how they approached the problem.

 

[Carnmore]

I have a similar rubble stone wall house with lime mortar. The house was renovated in the early 1980s and a timber stud and plaster board system was put against the outside walls. The outside was wet dashed with cement(non breathable). It worked for 30 plus years. We are now renovating it and putting breathable external insulation on and have removed the timber stud and plaster board internally and have replaced it with a hemp-lime plaster. It is excellent at smoothing out the variations in the internal walls and is a lot cheaper than lime alone. We have done 200 sq metres of it. There is a Facebook called cottageology- Irish cottage renovation and appreciation where a lot of different people have shared how they approached the problem.

Thank you - the external stone facade has to be maintained in this case. What way would you suggest insulating it?

 

[Andy836]

Thank you. Where would the air pocket be vented to?

You can install air bricks at a couple of locations (below the roofline, at the eaves and near ground level - your architect/builder will know where best to put them). Water is unlikely to come in through them unless the wall is exposed to significant rain and winds. If it is exposed to rain and winds then it might be worthwhile building a fence to protect the wall or plant some high growing strong bushes.
Most damp issues in old buildings are best solved by external design & maintenance - stopping water pooling at the base of walls or sheltering the walls from harsh weather, clearing gutters & downpipes etc.

 

[fear_gall]

There is a pavawall wood fibre insulation board from Acara concepts that could be considered.similar to gutted. Your walls need to be quite smooth to apply it. The Board costs ~€15 /sqm but the walls need to be lime plastered first. Some people add cork to lime plaster which has insulating properties. Ty-mawr in Wales has a lot of good reading on old walls and insulation.
Having said all that If the void created by the metal stud proposed is vented properly it should evaporate any damp.
There are different effective systems.

 

[bcon2019]

Hi,

just wondering what you went with in the end?
In the same position now and pricing up gutex 60mm and it aint cheap! €1500 for 22m2 board and adhesive and finishing plaster.
No damp in the house at present even with timber stud and 100mm rockwool set off the external walls but it's draughty house at present too.