Thermal Mass

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Thermal Mass

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Woo

Joined: 19 Sep 2011
Posts: 787
Location: Mayenne, Pays de Loire

Posted: Mon Jan 20, 14 7:48 pm Post subject: Thermal Mass

Does anyone have an opinion on insulating, or not, stone and lime walls?
We are pondering what to do next with the internal walls.
The building is built of stone and lime mortar and are 500mm thick.
We are considering using lime render to finish the inside rather than covering the walls with plaster, thus allowing the walls to breath. Also to allow the walls to act as a thermal store.
There has been a differance of opinion among those who have visited about damp?
any thoughts?

vegplot

Joined: 19 Apr 2007
Posts: 21301
Location: Bethesda, Gwynedd

Posted: Mon Jan 20, 14 8:53 pm Post subject:
If you want thermal mass it's better to insulate the outside of the building rather than internally. External insulation has been done on a number of houses locally here where they are predominantly stone and built in the late 1800's. Insulation can be breathable and have a covering of lime render (inside or out). So it really shouldn't be a problem either way.

Gervase

Joined: 17 Nov 2004
Posts: 8655

Posted: Mon Jan 20, 14 9:55 pm Post subject:

Consider a hemp/lime render internally - about 5cm thick. It will make a considerable difference to the insulation and move the dew point well away from the surface, while leaving the exterior of the building unaffected.
Alternatively you could batten internally, apply fibrous insulation (sheepswool, flax or similar), line with 12mm wood fibre board and then plaster with lime.
If external aesthetics are not a problem, then 2cm wood fibre board, plus a mesh plus an hydraulic lime render would be effective.

Ty Gwyn

Joined: 22 Sep 2010
Posts: 4563
Location: Lampeter

Posted: Mon Jan 20, 14 10:08 pm Post subject:
Surely a bit more clarification on the damp problem is needed first,whether its penetrating or rising.

Mistress Rose

Joined: 21 Jul 2011
Posts: 15600

Posted: Tue Jan 21, 14 8:07 am Post subject:
That's what I thought too. I would expect 500mm thick walls to give pretty good insulation as they are. Damp is something else.

Gervase

Joined: 17 Nov 2004
Posts: 8655

Posted: Tue Jan 21, 14 8:48 am Post subject:

Rising damp, so beloved of surveyors, is very rare. Damp on internal walls is more often due to penetrating moisture or condensation.
Ensure ground levels outside are lower than floor levels, that rainwater is carried away from exterior walls with good guttering and drainage, that the walls are breathable and that there is adequate air circulation and insulation inside, and you should kiss goodbye to damp.

Woo

Joined: 19 Sep 2011
Posts: 787
Location: Mayenne, Pays de Loire

Posted: Tue Jan 21, 14 9:14 am Post subject:

There is no problem yet as we are still converting this barn into a house.
The outside is stone and lime mortar which we dont want to cover. We have been making the surface flat by ensuring the mortar is flush with stone; thus, hopefully, making a good run off surface for the rain.
The damp was commented on by a visitor? not that there was any, but that there would be without plaster boarding.
Our feeling was the walls would create a heat store as well as a shield and if we covered and insulated them the only store would be in 1 cm of plaster.
The words 'It's all a big experiment!' and 'how hard can it be?' have been on our lips alot!!!
thanks for your interest.

vegplot

Joined: 19 Apr 2007
Posts: 21301
Location: Bethesda, Gwynedd

Posted: Tue Jan 21, 14 10:23 am Post subject:

Mistress Rose wrote:

That's what I thought too. I would expect 500mm thick walls to give pretty good insulation as they are. Damp is something else.

They act as a heat soak/store and being relatively massive end up being somewhere between mean external and mean internal temperatures. External insulation helps break the influence of the external temperature influence thereby increasing mean temp of the walls.

vegplot

Joined: 19 Apr 2007
Posts: 21301
Location: Bethesda, Gwynedd

Posted: Tue Jan 21, 14 10:29 am Post subject:

Woo wrote:

For the walls to be a heat store they need to be internal to the building and therefore the insulation should be external. If that is not desirable you could consider stone or brick internal features such as a large chimney breast, internal walls, limecrete floors floating on insulation etc.

Mistress Rose

Joined: 21 Jul 2011
Posts: 15600

Posted: Wed Jan 22, 14 7:30 am Post subject:

You will need to make sure that the floors are suspended or damp proofed of course, but no doubt you have already thought of that. If there is no sign of damp I would have a contingency in case it happens, but otherwise I would expect heating inside like fires to sort the problem out.

Our lounge seems to have a slight damp problem through the floor in the summer, but as soon as we get the fire going in the winter it is fine again. I have a feeling that the people that built the place didn't bother with damp proof membrane under the concrete flooring as it was meant to have a suspended wooden floor, but it never happened. We have lived quite happily with the situation for 30 years though, so not major.

Woo

Joined: 19 Sep 2011
Posts: 787
Location: Mayenne, Pays de Loire

Posted: Wed Jan 22, 14 9:15 am Post subject:

Mistress Rose wrote:

You will need to make sure that the floors are suspended or damp proofed of course, but no doubt you have already thought of that. If there is no sign of damp I would have a contingency in case it happens, but otherwise I would expect heating inside like fires to sort the problem out.
Our lounge seems to have a slight damp problem through the floor in the summer, but as soon as we get the fire going in the winter it is fine again. I have a feeling that the people that built the place didn't bother with damp proof membrane under the concrete flooring as it was meant to have a suspended wooden floor, but it never happened. We have lived quite happily with the situation for 30 years though, so not major.

Thanks for the reply. our floors have a DPM and will be tiled and have underfloor heating.
The wall issues have been postponed and we are currently pondering the roof insulation as the third floor has gone in and we can reach it!

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