Hi

We're about to renovate the dining room in our stone cottage, and wanted to ask for some advice on French doors. At the moment the room has one window on the north side of the house, and the room is quite dark. We want to put in French doors opening onto a patio area on the south side. The walls are very thick stone (around 2') and I'm concerned that putting in French doors is going to make the room much less efficient at keeping the heat in. Are French doors considered a bad idea from an insulation perspective, or will the additional passive solar gain be likely to offset the loss of stone enough to make it worthwhile? What are the best products to be looking at?

Thanks
Simon

I reckon there are lots of skilled joiners about - but many will not be up to speed on energy (& other environmental) issues, however given their making skills they could be briefed on that by a client.

It wuld be a very rare wall that was two-foot thick and made of pure stone. Most walls are rubble-stone, with thermal values that don't follow that of your standard limestone cube. There's been some interesting research by Historic Scotland http://www.historic-scotland.gov.uk/cgu-interim-u-value-mass-walls.pdf" >here which may surprise some.

Based on the historic Scotland document it seems very dependent on the internal finish. If hard plaster direct to the stone then a decent 2G/3G door could well be better. If it is lath and plaster, or plaster board then you'll need pretty high specification (i.e. expensive) doors to be as good, or better.

Add in the potential passive solar gain, and you should probably still end up no worse off though.