David

I have just found this forum and very interesting reading it makes too. As the proud owner of a damp lower ground floor with shot tanking, I would be really interested to know more about the various methods you describe in your entry of the 1st May above.

Could you do external insulation?

If you do your system how will you stop condensation forming on the walls, drafts entering in and arround the gaps in the insulation, thermal bridging of the studs?

The gap will tend to get damp if not actually wet. Plasterboard on its own will not do enough insulating to stop the thermal bridge.

I wasn't using the lasterboard on it's own. 600mm stonewall - vapour control layer - 50mm air gap - 70mm metal frame incorporaing the 60mm insulation - 12.5 mm plasterboard. Hope that's more clear though you're gonna say the same?

I do not trust U value calcs for below ground rooms as no one seems to add in the U value os the "soil". If it were mine I would lime plaster the whole room and forget insulation, having made sure no leaking drains or plumbing outside. There are some threads on here about this. Basically as the room is warmer than the soil behind the walls the partial vapour pressure of the moisture in the air in the basement is higher than that in the soil behind the walls so moisture tends to move from the basement into the soil!!!

There is no point what so ever in digging trenches -- may be the top bit near the ground could take insulation or even the walls above ground -- thats where insulation is needed -- and the basement floor most certainly does not need insulation. Where can the escaping heat go? Once escaped the soil becomes warm in fact it gets to the average temperature of the room.

Tony,

Some lambda-value for soil:

Ground conditions l-value ground W/mËšC
Clay, sand and gravel with drainage 1.50
Sand and gravel without drainage 2.00
Rock 3.50

There's a formula for calculating the 'equivalent ground thickness'. I'll see if I can find it again...

dachaidh,

No vapour check is not a good idea. As Tony says you need to have it on the warm side.

Why not just stick a PUR/PiR board straight on the wall (using suiable plastic fixings). The 2"x1" timber studs n top and screw your plaster board to them? Solid layer of insulation, no bridging. If you look at Kingspan, Celotex, Recticel, etc. This is the installation technique they recommend.

No between the insulation and the plasterboard.

I agree with fostertom's support for keeping thick solid walls free from insualation. Our cottage 600 feet up in Wales needs no space heating in summer ( May to Oct). All the rooms face south. But in winter the costs of heating are going to become unacceptable. So here's the question: How do I insulate the walls internally for just the winter months?

Posted By: dachaidhHmmm... so if you glue the insulation to the plasterboard where does the vapour check end up...?

Some types of insulation are also vapour barriers - extruded polystyrene over 50mm thick is as are foil-faced PUR boards. Expanded polystyrene is not a vapour barrier though. Don't forget to tape the joints if using a vapour barrier foam insulation though.

Paul in Montreal.

Posted By: dachaidh600mm stone wall
50mm air gap
60mm Kingspan with foil to the outside
50mm metal framing
12.5 plasterboard

That looks OK - but how are you fastening the Kingspan to the framing? I presume when you say "foil to the outside" that the foil side is facing the plasterboard? This would be the warm side and where the vapour barrier should go. Depending how uneven your wall is you may be able to use the extruded polystyrene boards that have furring strips built in and just tapcon them to the wall, fix strapping to the furring strips and screw the plasterboard to this - saving space and the need for the metal framing. So long as the extruded boards are at least 50mm thick they will act as a vapour barrier. If the wall is very rough, though, this may not be feasible.

Paul in Montreal.