Emerging realisation that thick massive walls can be a fair substitute for insulation - in other words, despite poor calculated U-value, actual heat loss is quite small. Due to long-delay heat flow, which may at least partially reverse direction. I'm hoping to find time to read and understand how this works, what the parameters are. Meanwhile, avoid internal insulation at all cost - throwing away your valuable resource of massiveness!

Thanks fostertom, but how can I satisfy Building Regs, will it help if I get some sort of calculation done. I can insulate the roof quite well and the new Limecrete floor using one of the "Big name" insulation products and they provide calcs to show that they meet B Regs and it would be great if the walls could be left alone and just pointed up but I think the Building Inspectors will want insulation added to them somehow.

Is that it then is internal insulation a complete no-no?

Trouble is, using plastic sheeting and the like is asking for trouble with condensation. That's the downside with 'standard ways' - the standard way with rubble stone walls in my part of Wales was (and largely still is) to repoint and then render in cement, inject a DPC and plaster with waterproof plaster internally. That's why folk round here complain that 'old houses are always terrible for the damp and condensation'.
Do you need to do anything other than three-coat haired lime plaster, maybe on laths nailed to 2x1 counterbattens?
Reference to the Chartered Institute of Building Services Engineers Guide A includes the thermal performance and U values for most materials which are available, for example the thermal conductivity of lime plaster is given as 0.8 w/mk while the U value for stone walls 600mm thick with 50mm air gap with 25mm of dense lime plaster on wooden laths is 1.38 w/m2
However, the point has to be made to the BCO that a U value is a mathematical calculation. A 900mm thick rubble wall will have very good insulation value provided it is solid. However, as stated above, all old rubble-stone walls have voids (which is why chemical DPCs are useless) and it is by no means certain what material is inside the core. Thus even trying to calculate a U value can be meaningless.
It is also worth making the point that thermal performance is one consideration. So are 'technical risks' and the general well-being of the building and its occupants. Clay boards and lime plaster are excellent in helping the 'breathing' performance of solid wall structures. Celotex, dry lining and cement can be disastrous, increasing condensation, damp and the like.

Generally in old barns etc the massive ventilation and absence of heating fails to reveal the problems of condensation and/or rising damp which will accompany habitation. I suggest, unless the walls are exceptionally wet due to rising damp, you render the walls internally with 6:1:1 to a flat finish and apply an insulated plasterboard using dot and dab gyproc adhesive. Its easy and gives an excellent flat wall. If fitting wooden joists, use joist hangers and douse the ends in preservative (or char black as eco-alternative). Not 'sustainable materials' to everyone's mind, but will provide a sustainable building.

With careful design a DPC may be unnecessary - and in my opinion a DPC is almost impossible to retro-fit in this kind of building,

david and Gervase Webb, that's very important, what you say about the wind blowing through the gappy interior of a rubble wall (no such problem with my Dartmoor cob farmhouse!)
If only the wall could be made airtight (not vapour-tight) at both inside and outside faces, especially outside, then the interior wouldn't get outside-air-cooled to the point where the wall is thermally only as thick as the "inner skin" or even just the plaster thickness. Is such external airtghtness impossible, with carefully done lime pointing? External lime render would do it, no problem.

Posted By: GuestPoint it up well and flush with lime mortar and then limewash it; the result will be a weatherproof but breathable wall.

That's good, Guest. Is the limewash essential? many places where bare pointed stone wd be reqd.

Posted By: fostertomExternal lime render would do it, no problem.

Or would it?
We know that cement render isn't airtight because it shrinks and cracks - into large pieces because being strong it resists cracking up to a point - and these relatively-wide cracks not only capillary-attract lots of water in, which then can't evaporate out because the crack/vents are too widely spaced - but also lets the wind blow through.
Whereas lime render micro-cracks into small pieces because it's weak - and these micro-cracks also capillary-attract lots of water in, but which *can* then evaporate out because the crack/vents are closely-spaced.
But do these micro-cracks also let the wind blow through? If so, I guess occasional limewashing would help seal them up.

Fostertom said
"That's good, Guest. Is the limewash essential? many places where bare pointed stone wd be reqd."

If you look at old pictures of stone cottages they are normally lime washed. The modern trend toward exposed stone walls is surely just another example of fashion leading function ?

I've used five different ways to insulate the interior of external random rubble walls. Some would say none of them are "Green" but when the energy saving over the twenty five years since the first job is taken into account, I reckon they are.
Breathability was never considered because we'd never heard of it, insulating old walls was very unusual then. There has not been any visible problem with damp or condensation, no damp smell when the owners come back from holiday. Houses which were damp and cold are still dry and warm.
These are the methods I have used in different buildings. I usually tried to retain the shape of the wall.
First method 25 years ago. Fixed treated battens to roughly rendered [sand cement] wall with Expamet Lath. Bent battens to wall shape, fixed 25mm polyeurethane foam over with galv. nails and then plasterboard over. This system has a shown a defect. The nail heads make a mark on the paint. Could be condensation on the nail head or static attracting dust.
Next time fixed same insulant to rendered wall with Ardurit adhesive then thick Bonding Coat and plaster skim over. Cut boards into small pieces to follow curvy walls.
16 years ago bonded insulated plasterboard to wall with Ardurit. Problem here was plasterboard edge joints failed because adhesive was dabs and not continuous. Ten years ago built 75 mm stud wall filled with EPS and DPM over. This is really making a timber frame house inside the existing building and using the stone walls as a rain screen.Works beautifully. Last job I fixed treated battens to wall wth stainless screws and plastic plugs, 2L2 foil and bubble insulation over, battens over that and plasterboard.. The house was 9 inch solid brick and cold and damp. It's now dry and easy to heat. 2L2 is almost no plastic and a tiny bit of aluminium. Why is it neccessary to look for solutions to all modern building problems in old methods? When houses had damp floors and lime plaster and no insulation they were cold and damp but this was normal for the occupants. When I was a child we had one heated room and frost on all the windows. Expectations change and I don't think it's possible to meet our expectations of comfort with a coat of lime plaster on the inside of your wall. The outside is another matter. Whether a particular material is "green" depends on where you're loooking from. Sheep have destroyed our upland landscapes but their wool is green! If you live in Derbyshire limestone quarrying is not green! We need a more flexible view of green .All Insulating is green. All methods damage the environment.

Do you have to insulate the walls at all to get the scheme through building regs? If not, then what about externally insulating using your permitted development rights (if these apply to holiday cottages???) after the job has been signed off and the council are off your case?

Although I have no experience in this area, I would be concerned that isolating the walls from the warmth of the house might not be good for them long term i.e. could allow damp to build up etc??

We have exactly the same scenario with the 'triangular' stone. I was just wondering if the untreated fleece from our sheep (that we sheared off them and haven't found a good use for yet) would be a nice replacement for the glass fibre, especially in the gaps on the inside.

Barcud,
Shame that the insulated plasterboard will not be durable enough for the long haul. What worries me if the
the insulant is gas based is that the off gasing will reduce the board insulating level down to nearer air based
insulation. Trouble is that people opt for the foam boards to get thinner insulation. How well will the boards
stand up to the rigours of being on an external wall with temperature differentials ie inside temps and outside.
Shrinkage is bound to take place introducing potentials air gaps. Also knocks form occupents and wall fixings.

If you go for the plasterboard I would think carefully about getting the walls as flat as possible with a durable
levelling plaster especially if you have timber lintels, window frames etc as you will not trap moisture.

Have you considered wood fibre boards on a clay/lime leveling render. You can skim plaster directly on the finish which will knock about 12mm of the depth in comparison to the insulating plasterboard which will also
need a skim. The boards are going to be more stable in the long run and with more thermal mass.

Also as fostertom point out U-values are not the only issues. Shame that the UK building control
seems to be years behind others here. Anyone who lives in a stone house should be aware of the effects
of thermal mass. I the recent warm weather my stone walls have kept the temperature in my house very cool.

I read a recent publication by bre www.est.org.uk/bestpractice and thought it lacked scientific rigour. In the
end people simply don't know the best way to renovate old properties and we the interested public are left
in a state of limbo.

Good luck.

Barcud

Trial installation of Spacetherm lining used internally on a local authority flat in Scotland completed recently. Full thermographic scan before and after showed an improvement on existing average U value of 0.628 W/m2K down to 0.35W/m2K.
The Spacetherm lining was fixed directly to the internal wall and comprised 2 x 9mm layers Aerogel fleece bonded either to 9.5mm Gypsum board or 10mm Fermacell i.e. a total thickness of less than 30mm.
That was rather convenient as an existing dry lining of timber battens and plasterboard with a thickness of 30mm had to be removed thus there was no net loss of internal space. Not the cheapest solution, although less expensive than external, but certainly by far the thinnest. Have a look at www.spacetherm.com

"I have looked into wood fibre boards but I think I would have to use about 200mm"

Barcud,

100mm diffutherm board will give you 0.37 w/m3k on 215mm brick wall. You should be able to calculate
the figure for your stone wall. the layers of render will be about 10mm. That's 101 in total. The boards are
tounge and groove so no air/vapour gaps, no worries about thermal bridging. My front room is small I'm in
a mid-terrace but I still intend to use the pavatherm boards partly because I only need about 10 boards so
although it's pricey I don't really worry about 150-300 pounds. I ruled out timber stud method as I thinks it's
trickey to get it air tight and I don't want to be worrying about interstitial condensation. Another thing for me
is that it can be noisy outside the house and the extra mass of the wood fibre boards will help with sound
insulation.

Ideally you should be rendering the outside of your barn with the woodfibre and then putting on a beautiful
lime render. and enjoying your stones on the inside. We tend to have cob barns around here and they
are rendered in either earth or lime, the stone foundations are usually visible though,

I'm intrigued to know what waterproofer allows the fabric to breathe.
To repeat, you don't these 'wonder materials' (none of which is particularly green) if you address the source of the moisture and look at drainage, guttering, ground levels and breathability.

Posted By: BarcudOne development though is that the local Building Inspectors want a 'U' value of 0.35 and after some searching on the internet and phone calls it looks like the only way to achieve that without losing too much space with a huge thickness of insulation would be to use a "modern" insulated plasterboard on treated battens, not exactly what I was hoping fo

...that's my experience also, there's a tricky balance between building reg's & barn insulation & sustainability & space ... one alternative I've found to the modern insulation & plasterboard solution is Heraklith wood boards (that are sustainable) and Thermafleece Sheepswool Insulation. I've not properly priced them but I believe that is a more experience & bulky, BUT sustainable alternative.