Insulation u value wanted.

[robgraham]

I've an old cottage. Our bedroom ceiling - lathe and plaster - is passed it's best and I'm going to reline it with p/b over a timber frame. It did just strike me that the cavity so created should be filled with insulation, but before I do all of this, I would like to calculate reasonably accurately the heat losses through all the surfaces. There's 6" of fibreglass in the attic.

Two of the walls are external and stone structure. Can someone give me a usable U figure for a stone wall that is 560mm thick and consists of an inner and out stone skin with loose rubble in the middle. Inside this is 50mm of rockwool and then p/b.

I haven't looked at u tables recently but what is the influence of a carpet and underlay on a wooden floor with plenty of underfloor ventilation ?

An alternative thought to using u values is to take the room air temperature and then IR thermometer each surface; can that be used to work out the major heat loss ?

Thanks

Rob

[RobertL]

Think twice before you pull it down. I had such a ceiling and pulled it down (for woodworm treatment in fact) planning to insulate above it and replace it with plasterboard. But Building Control got wind of this work and informed me that I had made an "unauthorised alteration to a thermal unit" and that I needed to file a regularisation application (=A3120 IIRC) for it and get their approval for what I wanted to do. It then had to meet modern building regulations for insulation. I am having to lower the ceiling to fit in enough insulation to meet the BC requirements.

Once you pull it down you aren't allowed to simply put it back.

Robert

[meow2222]

Maybe OP means he'll leave the L&P there and add battens and PB.

Refixing an old L&P ceiling and skimming it isnt really any more work though. Less really.

NT

[Mike]

£120 quid down the drain to achieve nothing. Bugger building control, put the insulation you deem necessary, stick the plasterboard back up and then ignore them. What are they going to do, insist you pull down the ceiling yet again only to put it back up? F*ck 'em. Parasites!

[sm_jamieson]

How did they "get wind of it" ? Simon

[Rob G]

I would help, guys, if you answered the question rather than going off onto another topic because you didn't read the posting correctly - I did actually say that the new ceiling plasterboard was going onto a new frame and there was to be a cavity.

It's a bit unfair of you to take advantage of my posting to make your rant against BCO's.

Rob

[george (dicegeorge)]

ooopa - i have some lathe and plaster ceiling which has collapsed due to a burst pipe, am i allowed to patch it with a plasterboard patch? i was going to replace a few square yards with plasterboard and insulation, but now must think again must i?

[g]

[Hugo Nebula]

On Mon, 9 Mar 2009 06:29:18 -0700 (PDT), a certain chimpanzee, robgraham randomly hit a keyboard and produced:

From the top of my head:

Outside surface resistance = 0.04m^K/W Limestone: conductivity = 1.13W/mK; divide the thickness by this value to give resistance. Mortar (and presumably loose fill): conductivity = 0.84W/mK [1] Rockwool: conductivity = 0.05m/0.038W/mK = 1.32m^K/W [2] Plasterboard resistance = 0.06m^K/W. Inner surface resistance = 0.13m^K/W

Add up all the resistances, then take the reciprocal to give your U-value.

[1] It depends on the proportions of wall to rubble-fill, but I would have thought about 75% stone to 25% mortar and crap, which gives an average conductivity of about 1.04W/mK. [2] If you want a precise figure, you should also include for the studs in the dry-lining.

R = 0.04 + 0.56/1.04 + 1.32 + 0.06 + 0.13 = 2.09m^2K/W. Therefore U-value = 1/2.09 = 0.48W/m^2K. To work out heating, probably best to use 0.6-0.8 unless you can put actual values to the thicknesses of the leaves of the wall.

[John Rumm]

yup. You can do what you like with a repair generally.

Even for work carried out under a building notice, most BCOs are quite pragmatic, and work on the principle that it will not always be possible (or even desirable) to meet modern standards on an old building, and if you make sure what you put back is no worse than before, they are happy.

[Rob G]

Many thanks Hugo - I should have said the stone was sandstone and whin but the values won't but be that much different and anyway the percentage stone/rubble will be a guess.

Rob

Rob

[The Natural Philosopher]

sounds like a plan. Use celotex and make it utterly airtight.

Not good, The walls are next to bugger all, and although 50mm of rockwool is better than nothing, 50mm of celotex is about twice as good.

Not nearly as much as totally draughtproofing it. Nail hardboard over it and seal with duct tape and re-lay carpets. Or lift whole floor, and put clotex betwen joists, tape up and re-lay floor.

Not a bad way to at least ID cold bridges and the like.

[Martin Bonner]

ABSOLUTELY! I was thinking of dry lining one wall of my kitchen (currently just 9" brickwork). I was trying to get down to a fairly low U-value (the current new-build standard). It looked fairly straightforward until I factored in the studs - half the heat was going through the studs, and half through the celotex between them! (I wanted studs so I could screw things to the walls. I think the solution is an overall 25mm layer of Celotex + studs with Celotex infill for the rest.)

[Rob G]

Celotex wasn't available when this was done !! And you don't realise just how effective it was - the cottage was modified in the 1920's to lift the stone slab floors, dig out, ventilate and lay suspended wooden floors - then they added lathe and plaster to the original distempered stone walls - unfortunately they didn't control the underfloor ventilation going up behind the L&P to the roof space so the whole house had zero wall insulation in the winter gales. All L&P had to be removed and insulation added.

I don't know what sort of floors you live with but my floors are good quality T & G which I'm not detecting any draughts through. I've a self made electronic draught detecting thermometer.

Rob