We are renovating a very old farmhouse. It is not listed. Most of the walls are around 20" thick or thicker, made of stone (brown slate) with cob or lime mortar. It is not rendered externally (although the walls have been painted in places with what looks like an unbreathable paint.) Various other bodged and unsypathetic works have been carried out on the house over the decades eg UPvc windows which have failed & hardboard/fibre board drylining. In one section of the house we want to gut the house internally, remove the drylining and existing fibreboard partition walls and re-configure the room layouts (we have checked and do not need PP). We would like to go back to the stonework internally and bag-lime plaster the walls so that we max interal room dimensions and can see the shape of the stonework. Our architect is telling us, under the building regs, we have to insulate internally by drylining. Excuse my ignorance but is this true? It seems to me that this would compromise the character of the property and that the walls I would end up with, would look the same of those in a 70s semi which is not what I wanted. And on theses forums and elsewhere I have seen reference to research into 'the thermal mass of solid stone or brick walls, which stabilises internal temperatures and can make buildings more energy-efficient than they might seem'. Is there anyone, please, who could point me to such research so that I can bring it to the attention of the architect/building control?

Could you insulate externally? what is the existing wall finish?

Thanks to all for taking the time to comment. Its so depressing that an arbitrary measure that seems to be based on bad science means that gradually all our old building stock is going to be turned into featureless rectangular boxes. I wonder if we should apply to be listed...

Tony - the external walls are stone with lime mortar – no render but some paint – but at least on the north wall, insulating externally would cover/spoil some important features. The east wall of the section being discussed is very thick stone but is itself an internal wall. The west wall is a party wall. The south and west walls are in not so good condition. Has anyone ever seen a mix & match approach accepted – eg exposing and lime bag rub finish/or spray insulating plaster on the north and east walls, and dry lining/insulation on the south and west walls?

Also does anyone have any experience of using an independent building control inspector rather than the local authority BCO?

Mike - effectively with what I am suggesting, only 2 of the walls would end up insulated. The other 2 - one external and one internal - would be uninsulated stone, although maybe they could have a coat of Hemcrete if it would preserve the contours.

Yes, you only need to do walls between you and the outside air. Not between you and next door or any other internal wall.

Also, it may be worth you looking at the detail in Part L1b http://www.planningportal.gov.uk/uploads/br/BR_PDF_ADL1B_2006.pdf

Page 7 para 4a on

I appear to have found a rather odd way of approaching the Building Regs issue. My BR officer said that it was only the carbon output/heat loss in the end that was being measured .... so I volunteered to get my carbon count down and run heating and cooking on wood, and they appear to have agreed to go with that.

I hope that helps someone in some way.