Old House, Stone walls, Cement Render, Internal or External Insulation

Postby Jigsaw1980 » Wed Jul 24, 2013 9:59 pm

Hi Guys,

Been researching this for ages and need some advice. Bought an old house (circa 1860), 2 foot solid stone walls some damp issues (sources of which mainly found and some hopefully sorted).

Been looking at insulation both internal and external. I like the idea of External and got a quote for it. The quote seems to use all non breathable products. Additionally the house has an external cement render (i know its bad).

By putting a non breathable insulation layer on the outside (with acrylic render which apprently wont crack) on top of a non breathable cement render (which has a few cracks) will it make things worse rather than better? My understanding is that water wont get into the walls from the outside but Im concerned that the moisture generated inside the house will have no where to get out.

Would i be better doing internal insulation using breathable materials and use lime plaster with an air gap and (eventually) remove the cement render and replace with a lime render (am dreading this as its a massive job!)

Any ideas greatly appreciated!

Many thanks!
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Simply Build It

Postby welsh brickie » Thu Jul 25, 2013 11:36 am

its always best to insulate the internal area as escaping heat will rebound back into the rooms quicker than external insulation, The problem is you lose space.
The best solution is to frame out the internal walls with 50mm x 50mm battens insulate inbetween then vapour barrier and plasterboard, all the services, cables, and pipes can be hidden giving a clean insulated area, But you can also leave wood beams exposed and plaster the walls rough to give the appearance of old plaster
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Postby Jigsaw1980 » Thu Jul 25, 2013 3:27 pm

Hi Welsh Brickie. Cheers for the reply. Had originally planned to go with internal insulation but then lots of sites were saying that with internal insulation its less efficient as the natural heat build up in the walls is lost. It really is a minefield topic with everywhere saying different things. The majority of sites ive found that reference old properties state that breathability is key. If i put a vapour barrier on is that not going to affect the breathability? My original plan was similar to yours:

* to remove the existing internal plaster form the walls as it is damp and contains salts
* have a cavity between the walls and the insulation
* batten and insulate
* plasterboard
* plaster

My concern though is as the walls outside are cement rendered and if i have non lime plaster on the inside then when the water gets in there it will have no where to get out unless i remove the cement render or use internal breathable insulation and lime plaster?

Reference sites ivefound useful in case they help anyone
http://www.english-heritage.org.uk/publ ... lid-walls/
http://www.heritage-house.org/pages/man ... dings.html
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Postby DrNick » Mon Aug 05, 2013 12:35 pm

Jigsaw1980 - Hope you don't mind, but I am in a very similar position to you so thought I would bump this thread with a couple of additional questions rather than starting a new one and having the info spread about...

We have recently acquired a c1850 stone farmhouse that has been unoccupied for some time and sounds very similar to yours. Obvious sources of damp identified and hopefully under control etc. We're not considering external insulation so what we really want is an answer to your question about membrane-lined insulation board for inside the external walls. What's the best option? Are 'breathable' products available or am I really going to have to start shearing the local sheep in the dead of night and making my own?


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Postby Perry525 » Mon Aug 05, 2013 5:52 pm

You need to understand how insulation works.
If you place insulation on the outside of a home, then you have to heat the walls, the ground and the sky.
The reason is, that your heat warms the surface of the walls, your heat then moves though the whole of the wall, and passes into the ground by conduction and radiation, and into the sky by conduction.
If, on the other hand you place the insulation on the inside of the room, floor, walls and ceiling, you create a plastic insulated box, that is both heat tight and air tight.

To avoid having any heat bridges, you should glue sheets of polystyrene to the walls and then glue plasterboard to the polystyrene. The floor must be fully floating, sheets of polystyrene just laid on the floor, tightly butted, with a Oriented Strand board t&g glued floor to finish (no heat bridges). The ceiling is much the same, sheets of polystyrene below the joists, followed by plasterboard screwed to the joists.

This will keep all the water vapour that you produce inside the room. You can open the windows for ventilation, this will also allow the water vapour to escape. It is nearly always colder and drier outside than in.

Water vapour that you see outside as, dew, frost, ice will remain outside. While the sun will drive some water vapour into the walls (as they are colder) this will disappear as the walls warm.

As the building is old and without a damp proof course, the water in the ground will continue to rise inside the walls as it always has and it will continue to evaporate into the air, as it always has.
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Postby DrNick » Tue Aug 06, 2013 9:14 am

Thank you for the reply Perry525. This is exactly what I read the general advice to be, however on speaking to people about older stone buildings, the consensus seems to be that fully tanking the inside is a recipe for disaster, and that both sides of the stone need to breath, not just the outward-facing side, otherwise structural issues with the stone work will follow.

We have no evidence of rising damp, just damp penetrating from earth piled up against a wall outside and some ingress from the roof. Our thoughts were that once these issues are resolved and the place has dried out, with a breathable insulation material, board and lime render inside, damp should not be an issue? Do you have any thoughts on this? I appreciate your advice, but I wonder if the techniques for 'sealing' up modern houses are really the best way to go for an old property?

Thanks again,

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Postby Jigsaw1980 » Tue Aug 06, 2013 10:20 pm

Hi Nick,

Thats the impression i had gotten as well about old properties and have concerns that modern day insulation techniques are being blanket applied to Cavity wall, solid walls and solid stone walled buildings whereas they all are very different in their construction. I think every situation is different and you can only try to pick one that best suits at the time.

Im still not sure if my ideas posted earlier is the best option but i believe it still allows an amount of breathability between the inside and outside (due to the cavity gap) which will also prevent moisture bridging across. Then ill probably remove my cement render on the outside and lime plaster it to allow breathability on the outside. Additionally i think this enables you to decorate whatever way you want internally without having to worry about lime plasters and lime wash whereas lime plaster inside limits your decorating options to breathable paint which doesnt seem to be as easily obtained and is less hard wearing.

One other question i have is if you were to go with external insulation (i know its been noted as a potential bad job) does this mean you would have to make the internal walls breathable i.e. lime plaster etc or could you just go with normal plaster? If the external is rendered with a non breathable acrylic render then it wouldnt be (supposedly) permeable from the outside so does it need to be permeable on the inside.

It really is an expensive minefield and im worried ill spend a fortune on something ill end up ripping out in x years time!!

Thanks and Thoughts?
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Postby DrNick » Wed Aug 07, 2013 10:04 am

My understanding is that the walls need to breath from both sides, otherwise there will inevitably be moisture build up on one side or other.

My bedtime reading yesterday was the report of the 'Changeworks' foundation who were commissioned to report on the state of "solid wall insulation in Scotland" in 2012. You will find it if you google it. It has a lot of very up to date information and recommendations, but the overall impression is that there is little or no consensus and that it all depends on specific circumstances. We certainly cannot afford to bring in a heritage building 'expert', so it will come down to applying common sense and hoping for the best I think!

Essentially the report concludes that complete water/vapour sealing with modern insulation, either internally or externally, is almost never the right approach. Breathable materials are the best and safest options and no more expensive. The issue is that the companies that install said insulation usually charge much more than those that use conventional materials.

We were thinking of going DIY with aluminium stud mesh a cm or so from the inside of the stone to provide breathing space, followed by thermofleece (sheepswool), followed by compressed woodwool board and skimmed with a non-hydraulic lime/hemp plaster. Doing it DIY, I reckon this would come in under £2.5k for materials for our decent sized cottage, but of course it wouldn't then be certified so we wouldn't get the relevant government subsidies on heating. Requires more investigation methinks! Let me know if you make any progress!

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Postby welsh brickie » Wed Aug 07, 2013 3:55 pm

I have read these posts with interest, my original reply I still stand by, and having used the method on stone house conversions I haven't had any issues.
As I suggested if you frame out the wall off the stone, damp cannot bridge the internal gap and besides your insulating the walls which will save you hundreds of pounds in fuel costs.
that's my opinion anyway.
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Postby Jigsaw1980 » Sat Aug 10, 2013 8:23 pm

Hi Welsh Brickie,

Is it ok to have an air gap between the wall and the insulation boards? My walls were previously damp and id be worried that with my external render (which isnt in great shape) if water gets in it wont get out again at the outside and will penetrate through into the insulation. Additionally the walls are stone and fairly un even so i dont think i could attach to the walls without having small air gaps anyway and wouldnt be too keen on attaching wooden battens to the wall in case they rot.


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Postby welsh brickie » Mon Aug 12, 2013 9:22 am

for the inside,if its damp, I usually point the walls with a lime sand cement mix to a height of 1 metre, then paint it in buitumin 3 coats, basically tanking the walls,don't attach the battens to the wall, if your using 50mm x 50mm treated timber you can fix to the ceiling joists, and fix it to the floor its strong enough to be self supporting, basically a partition, but your able to have your wall straight and standing off the stone so damp cant bridge across,
As for the exterior use lime cement and sand mix, of 1.1.6 hope this helps
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Postby DrNick » Mon Aug 12, 2013 12:56 pm

Great info - thanks!
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Postby TheHandyMan » Tue Jun 03, 2014 9:03 am

I have recently been looking to address the same problem recently and was entirely bamboozled on whether to go for internal or external. There are products out there with thermal insulation properties that keep your heat retained and they use some form of patterning technology to do so. I'm not entirely sure as it is not me who deals with the insulation side of things, that is in the hands of my brother. Though I do believe the product I recently brought is external insulation and is required to be placed on the underside of tiles on my roof.

I bought the Acti's Hybrid system, combining all three products for a complete system that insulated the roof of my roof house. I do believe this single product would do the job if external insulation is what your after. --- It is also a breathable membrane. http://www.jjroofingsupplies.co.uk/acti ... brane.html

Let me know your future choices as my work partner is looking for varying insulation for his company.

Kind regards,
Jack aka the Handyman.
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