Thermal plasterboard

Just had a bloke round about cavity wall insualtion and I've been told that I can't have it. It's a stone built property with an inner leaf of brickwork. Apparently because the inner side of the stone is jagged it can cause damp problems. I'm thinking that I'd like to insulate from the inside now so may get in touch with the plasterer who is due round next week.
Can anyone please tell me...
What are my options? For ease would rather use dot and dab plasterboard. How much is it? Is it worth it? How does it compare to cavity wall insulation?
Cheers, Matt
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RatRibs73 wrote:

I know what I would do, and thats frame the inside with 2x2, packed out using a ply membrane to keep the damp out, and using spacers of scrap to get it true, infill with Celotex, tape up firmly with Al. tape, and slap 12mm foil backed plasterboard on the inside, skim and paint. After laying in new cables of course..and pipes where appropriate.
I guess you could slap up insulation backed board with gobs of no nails or whatever..but its a bit of a hack..
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Cheers,
Whats ply membrane, celotex and AI tape. Time may be a problem with this solution. Plasterer is coming round Thursday.
Is the cost of doing this worth it?
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With energy costs up 70% in the last year, I say yes. 50mm Celotex will give terrific insulation. Maybe explain the situation to the plasterer, he may well have come accross this problem before.
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RatRibs73 wrote:

Celotex is a stiff polyisocyanurate foam board with foil on both sides. Its rigid, its easily cut and it has twice the insulation properties of anything else. You wedge it between timber studwork, and use aluminium tape over it all to create a water and draught proof seal.
Ply membrane is a typo. damp proof membrane - usually polythene.

Absolutely. Turns chilly rooms into cosy rooms.
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The Natural Philosopher wrote:

I didn't know that (the Al tape bit) - makes sense, and glad I found out as I'm doing exactly this job at the moment (qv my recent query on drylining a kitchen).

Heh, I was scratching my head over the ply membrane! But do you really need the DPM anyway if you have a clear air gap between the studwork and the wall? (And the insulation is foil-backed?)
David
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Lobster wrote:

No, but belt and braces, and you have to fix the studs to something..typically what you want is surface finish, then vapour barrier (the aluminium tape, and the celotex facing) then studs and celotex matrix for insulation. At this point you get cold and condensation make take place in the gap..so you want to try and both keep the studs clear of damp wall, and also allow perhaps moisture to permeate outwards through the wall - or provide ventilation (airbrick etc)
Its a fine point. If the celotex and al tape is good, then no internal moisture will penetrate, and the only damp will come in from the outside, and can leave the same way. Then a poly membrane will keep it away from the cavity.
OTOH if you HAVE got moisture from the room seeping in, then the last thing you want is to trap it in the wall..
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Umm.. I've been consorting with architects and they seem to have latched on to *insulating the inside* in a big way.
OK for plain walls (so long as you have floor standing shelves) but I'm trying to repair and insulate some Victorian barns which have a mix of 9" dwarf walls topped with 4" studwork and exterior feather edge boarding. To retain any visual interest in the construction I need to insulate on the outside.
They have suggested insulating the brickwork internally and putting insulation between the timbers. Is condensation likely to be an issue?
I have to rebuild the wall anyway and would find cavity work easier than 9" solid.
Any pointers to how others have approached this problem?
regards
--
Tim Lamb

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writes

. Why don't you look at how we build wood frame houses in Canada!
These commonly have 2 by 4 or 2 by 6 wood stud walls which are heavily insulated.
There is much emphasis on a well sealed non-permeable vapour/air barrier on the 'inside' or warm side of the wall structure, including careful vapour sealing around electrical outlets etc. in exterior walls. The most rigid standard, R-2000 also requires the use of an air-exchange which exhausts stale air, brings in fresh air and in the process recovers much of the heat from the outgoing air.
On the outside of the wall underneath any 'cladding', including brickwork which here is rarely used structurally, the use of a permeable 'building paper' or product such Tyvek is normal/required. Outside finishes can be wood siding, vinyl siding, occasionally metal and more recently a product that looks like wood clap-board (lap-siding) but is made of cement. Very occasionally stucco. See note:
One other thing that I recall for this particular climate (eastern maritime Canada) which is wetter and generally colder (for longer) than most oft the UK, is that 'not more than one third of the total insulation should be inside the vapour barrier. The reason being to not allow warm and therefore moisture laden air to permeate into the wall and condense at some point within it causing wet insulation and/or rot and mould.
We have used vapour barriers and Al. foil in the walls and insulated ceilings of both house we have built and lived in since 1960. Adhering to the principle and standards espoused by CMHC (Canadian Mortgage and Housing) has certainly been worthwhile. No rot, minimum draughts, low maintenance, little paint peeling etc.
BTW it's wise also make sure of sealed ceilings and a well ventilated attic; failure to do so can cause attic condensation and roof rot! IIRC the minimum 'distributed' venting is 3 sq.feet per 1000 sq. ft of area, 0.3% (by area not volume). Most house have much more than that, with frequently or continuously vented soffits and/or gable-end and/or roof vents.
Note: A neighbours house one year older than ours, later had some sort of sprayed on coating with a slightly rough 'stucco like' texture instead of stain or breathable-permeable paint. It was applied onto the conventional wooden clapboard (lap siding). Once completed the previous owner claiming that he had solved the repainting problem for life. He's dead and gone, rest his soul. But the present owner reports that the sprayed on finish is cracking and peeling possibly due to moisture finding it's way out through the walls? I always wondered about the validity of the inside vapour barrier since original owner did much of the building himself; as did we all in those days! Present owner reports some evidence of mould in a few places in some walls. Also the slightly rough finish gets grimy, suggesting that even if it survives the house exterior will have to be repainted anyway.
Our house has pine clapboard siding and again this summer will need restaining (always use a permeable stain not paint) and some repainting of the trim. This will be for about the fourth time in 36 years; I will most likely again do it myself (age 72) using a couple of trestles and planks for most of it. Happy to report that this house passed insurance inspection recently and the addition of a couple of requirements will reduce the annual insurance premium somewhat.
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On Sun, 5 Mar 2006 19:03:02 -0330 Terry wrote :

Particularly on the latter do you not get problems with the studs acting as cold bridges and causing pattern staining?
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Tony Bryer wrote:

Cold bridges yes, pattern staining no.
However if enough insulation is used, the overall U values are good enough for the regs.
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I had in mind to leave part of the studs visible so staining is not an issue. The most convenient place for the membrane is between the frame and the outer insulation. I suppose it would be easy to leave an air gap behind the boarding. Feather edge is not *airtight*anyway.
The structure would be studs infilled with plasterboard and 25mm insulation, vapour membrane, 25/50mm exterior insulation, battens (long screws:-) and feather edge.
This totals around 200mm so fits the architects idea of 9" supporting brick but means any *nice* brickwork being hidden behind internal insulation. I'm inclined to do cavity work and put a shelf along the top to hide the ledge. Somebody will perhaps advise on closing the cavity:-)
Meanwhile I'm off to search the farm for bits of discarded Oak to replace that rotted by the previous owners ignorance of ventilation.
regards
--
Tim Lamb

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When it comes to installing insulation sticking to the regs is silly as they are so poor. Always go over by a great margin, and fits as much as you can in.
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writes

They make the best. The Canadians have the R2000 standard, which is one the most advanced in the world, if not the most. The Canadians, say "build tight, ventilate right". The Canadians are implementing the R2000 standard in the UK and Japan. Canadian companies have be involved with UK companies, as the UK companies just don't have the skills levels, or can't concentrate long enough to carry out detailed work.

The exchanger is not manadtory but is generally used.

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Terry wrote:

Not just canada. This is essentially what my 2001 UK house is built like.
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writes

With those single glazed windows you put in?
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Thank you. An excellent description. The UK does not experience the extremes of weather found in Canada but we think we win on humidity.
I am interested in the purpose of the permeable paper?
regards
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Tim Lamb

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Tim Lamb wrote:

So was I.
It seems to be that water will run down the outside of it, but wind will not go through it, and moisture can, in time, percolate through it from inside the walls.
I.e. it ensures that there will be no build up of moisture inside the walls, whilst providing a showerproof coating.
My walls are
- 12x12 oak frame infilled with 7x3 studwork. On a double brick cavity wall with rockwool battens inside.
Then layers from the outside:-
Render over mesh, onto 1" battens (airgap behind the render, open at the base to allow any possible water ingress to drip out I suppose. Then building paper, then 12" waterproof ply. Then the studwork, with rockwool filled cavity to foil backed 12mm plasterboard laid over the softwood studs and TO the oak frame.
In an ideal life I'd have used celotex for even better insulation.
This construction entirely satisfied 2000 building regulations.
The structural strength given by the ply cladding is amazing.
The only drawback is you can feel the whole frame tremble when someone slams a (very heavy solid oak) exterior door :-)
The exterior could have as easily have had weatherboards instead of the render/mesh. There is no structural strength in the render - its purely there to keep he driving rain off.

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writes

A double brick cavity wall? A dwarf wall?

12" ?

There is a huge cold bridge via the studs.

Which was pretty poor.

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Right.
When my farmhouse was *re-modelled* the specification was ....feather edge or cement render on expanded metal over 25mm foil backed insulation between battens. Then a vapour barrier over the original render (they had to grit blast off the paint to restore permeability). The 4" stud work and lath and plaster were left alone. I doubt it would meet current regulations but it is !"$%^& warmer than it was:-) I claim to have originated the tale of the hot water bottle that froze on the bedroom floor.

12"?
Oh. I have been considering an internal steel frame to strengthen a 2 storey barn and wonder if this might be an issue.

Huh! I am rebuilding a redundant cowshed and have found that the internal render was actually supporting the roof. Around WWII the ministry of agriculture decreed that dairies should have a white, washable internal surface. This was most easily achieved by nailing up mesh, slapping on a coat of the hardest render possible and giving it a coat of whitewash. What nobody foresaw was the effect of shutting off ventilation from untreated timber. The Oak studs and sole plate are more or less intact but the wall plate (pine) has simply disappeared.
regards
--
Tim Lamb

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