Dry lining, thermal properties?

[Donwill]

An external wall in an extension I'm building is specified as 0.34U value, made up as follows:- Externally rendered 100mm dense concrete blockwork.

80mm cavity part-filled with 40mm Kingspan TW50. Inner leaf 100mm thermalite block. Drylined internally with 9.5mm plasterboard and skim.

As this is a kitchen / diner extension, I'm keen to tile directly on to the thermalite and leave out the drylining in order to make it easier to fix kitchen cabinets etc. What will be the thermal effect of leaving out the drylining, and by how much will the U value be changed.Will the building inspector be interested? BTW the extension was started prior to April 6 2006. Regards Donwill

[Weatherlawyer]

I wouldn't have thought it would make much difference as it is going to be clad in kitchen units. There will only be a strip of some 18 inches between the worktop and the wall cupboards. And maybe another 18 above. (Not sure.)

I'd put the plasterbard strip in the middle to facilitate tiling.

But you can get a firm fix to plasterboard with a strip of baton. Just mark where the cupboards are going and fix the baton with shell fixings and no nails. Then screw the cupboards to the baton.

Put one underneath with masonry nails as hooks to hold mugs and stuff. Actually you can bury a par 2 x 1 batton in the back of each unit as the sides go past the back by that depth.

[salesguy]

Do not, repeat NOT tile directly onto the thermalite. They will almost certainly suffer drying/shrinkage cracks, which could cause the tile to crack or fall off.

Dry line & then fix the tiles on the p/board to remove an problems.

I sold Thermalite for 3 years, and I can't remember the number of shrinkage cracks I saw.....

SalesGuy

[Donwill]

Many thanks, I'll take your advice, I would hate to see them all falling off the wall. Cheers Donwill

[The Natural Philosopher]

Almost none. The kingpsan alone is about 90% of the insulation.

Do the sums yourself.

[Donwill]

I believe you add up the resistances as they are in series, trouble is I dont know what value to give to the individual resistances except for the Kingspan. I've not seen a figure given for the gap behind drylining, I assume it varies according to the gap dimension.So maybe you're right the magnitude of the change in U value will not exite the BI. Cheers Donwill

[The Natural Philosopher]

No, it won't. I have all the info and data and have dine similar calcs. However listen to the man who advises not tiling onto block directly - he seems to have a valid point.

[Hugo Nebula]

On Fri, 21 Apr 2006 10:55:29 +0100, a particular chimpanzee named "Donwill" randomly hit the keyboard and produced:

The wall construction will certainly give the maximum required U-value of 0.35W/m²K without the dot-&-dab. I would have thought it would give a lot less.

[The Natural Philosopher]

I think you mean minimum.

[Donwill]

Agreed!! as stated in my reply to him earlier. Regards Donwill

[Hugo Nebula]

On Sun, 23 Apr 2006 00:12:57 +0100, a particular chimpanzee named The Natural Philosopher randomly hit the keyboard and produced:

No, maximum. A U-value is a measure of the heat transmitted through

1m² of the construction per degree difference in temperature, and the lower the better. The requirements for extensions give a _maximum_ permitted U-value of 0.35W/m²K.