conflicting advice re. insulating solid walls

[brugnospamsia]

Dear group,

My home improvement programme is in danger of being held up due to conflicting advice I have received regarding how to attach insulated plaster boards to 9 inch solid brick walls built with lime mortar.

Brent borough council insist on battening and hence a generous air gap over brickwork with no waterproofing treatment applied directly to the wall :-

$FILE/BCCS%20Dry%20lining%20Solid%20Blockwork%20info%20sheet%20No.7.docA video made 10 years ago by a local university shows waterproof sand/cement render being applied then the insulating boards attached with adhesive dabs, the boards then being skimmed.

The outside of the wall is rendered and I don't appear to have problems with penetrating damp

yours,

"confused" of Bristol

[Peter Crosland]

The Council are simply requiring you to follow current building control standards. These change over time and what was considered appropriate ten years ago is often different from that now required. These rules apply across the country not just to Brent. Under certain circumstances they can allow a particular job to be done in a different way if it is considered appropriate.

[Rob Morley]

$FILE/BCCS%20Dry%20lining%20Solid%20Blockwork%20info%20sheet%20No.7.doc>

I'd go with the council - applying modern materials to old buildings can lead to problems when it disrupts the movement or breathing of the structure, which a waterproof render is likely to do.

[Mike]

$FILE/BCCS%20Dry%20lining%20Solid%20Blockwork%20info%20sheet%20No.7.doc>> A video made 10 years ago by a local university shows waterproof sand/cement

Knowledge on old houses has come on a lot in the last ten years. Look at

for a variety of articles on the subject.

We had to remove some of this waterproof render applied some twenty years ago as the wall had gone green. Removing it of course took some of the lime mortar with it so this had to be redone as well.

Once dried out, we used an average two inch gap (varies a bit as property is random stone), and again no waterproofing applied. Make sure the air gap is well ventilated. Upstairs is easy into the eaves but downstairs can be a real pig. You need to put in airbricks and monitor whether damp is collecting behind the insulation which of course is somewhat difficult to do as you have to leave temporary access panels and plaster these up later. If damp does collect you need to add more airbricks or a fan until things stabilise.

[brugnospamsia]

Gawd, it gets worse and worse !

One thing I'm trying to avoid is having to pay for too much skimming so I was hoping to avoid mechanical fixings. I wonder if I could attach the boards to the battens with adhesive ?

The main problem I see is the difficulty in sealing on the warm, moist side where the boards meet the floor.

Where adhesive is recommended it is laid in a grid to form sealed cells.

Perhaps a hybrid system would work with boards attached to the battens with adhesive and with battens along the floor well sealed to the wall with mastic ?

[brugnospamsia]

my idea :-

[N. Thornton]

insulated plaster

adhesive dabs,

problems with

If your wall had been unrendered life would be much easier. You could simply use a vapour barrier, PB and rockwool.

Unfortunately unDPCed solid walls should not be rendered on both sides, nor vapour barriered on both sides, since damp will slowly accumulate in the wall, and have nowhere to go. Injection DPCs do not solve the problem.

Since youre already cement rendered on one side, you dont want to be attaching any form of vapour barrier to he inside.

Yet if you use PB and glass wool, a vapour barrier you would need.

The possible solutions?

A. Remove external render, with real care to avoid damage, then proceed with vapour barrier internally. Dont cement render these old buildings, it can damage them.

B. Apply expanded clay in lime plaster to the interior. This gives insulation with no vapour barrier, retaining wall breathability, and without the damage cement sometimes causes.

C. Do nothing.

Your idea of venting to the loft might work, I dont know. It would make damp worse in winter, but then dry it in summer. But if you do that you will lose out on insulation value, and I didnt see where in your sketch the rockwool is going.

In principle I imagine you could install PB with vapour barrier and pipe the trapped air to a micropower drying unit, never heard it tried.

NT

[Roger]

The message from [e-mail] (N. Thornton) contains these words:

Not a solution I have previously heard of. How effective is that plaster mix as insulation?

I am in a similar position to the op other than I have 2' thick rubble filled stone walls and no external render.

[brugnospamsia]

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I was planning to use foam-backed plasterboard, though perhaps I would be better using thicker battens and seperate insulation (spaced from wall with netting ?) and foil-backed plasterboard - thus making the decorative layer "serviceable" ? would I be better off using soft insulation ?

I've just amended my diagram :-

[John]

SNIP

Why do you have this maina for fixing the boards with adhesive - whats wrong with plasterboard nails through the boards into the battens?

[brugnospamsia]

I'm trying to avoid paying a plasterer to skim the boards afterwards - hoping to use taper-edge boards and special filler.

If I could have used "dabs" it would have been a 10 minute job :-) yours,

"Skinflint" of Bristol

[brugnospamsia]

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I just realised I need to treat the upstairs and downstairs as one system

yet sure how I will achieve it .......

I'm beginning to wish I never started this !

[N. Thornton]

Fwom:brugnospamsia ( [e-mail])

would be

I just explained why it wasnt the best idea to use any of those, but you can do whatever you like in the end, its your house.

NT

[Mike]

I use it for floors as it needs to be a lot thicker than Kingspan/Celotex or even Rockwool. LECA (Optiroc) in a lime/sand mix to a foot or so depth definitely does lower heat loss through the floor though. A friend did put a thin layer of it as an outside render but this was on a 'best attempt' basis rather than trying to meet part L.

Same here.

[Mike]

Yes. The insulation is a lot cheaper that way as well.

[Mike]

I see you haven't discovered Gyproc Easyfill then ? :-) My wife can produce a plaster finish so smooth even the paint falls off :-) (well not quite but you get the point)

Yep - Do you have a solid or vented underfloor. If the later it is easy. For the former, the best solution is to actually build a false floor and vent this as well. Kingspan on the underside of the floor (i.e. similar to what you are doing on the wall) increases insulation considerably.

Also if the floor is solid, does it allow damp through from under (stone or tiles on soil, lime concrete, etc) or is it impervious to water (real concrete) ?

[Mike]

air to move effectively all the way from the underfloor to the roof. I would separate these out. Most damp is downstairs and needs more effective dealing with by inserting air bricks in the wall.

I found it easiest to mount the batterning to the ceiling and floor. The only point it touches the wall is a couple of spacers into the wooden lintels above the windows for some extra stability.

The seals you show would be top and bottom I assume. Using glued on coving and skirting is one option.

Don't you have eaves in the roof ? If so the air should turn right and feed out there. If not you've got a problem as the damp will accumulate there.

Yep - know exactly how you feel. But our old farmhouse now takes about a quarter of the heat it took to heat before I started and the damp feel to the air has gone.

[brugnospamsia]

In an ideal world I would have nice brickwork and would have the head for heights that would let me repoint, but all the houses in the area are rendered. I think they must have used sympathetic stuff as I don't appear to have rising or penetrating damp problems.

(100 year old photo of identical style local house showing budget construction and major neglect 40 years after construction .)

The one thing to my credit is that I resisted having the front wethertexed !

Having "expanded clay in lime" plaster done sounds extremely expensive (finding a local plasterer who knows what it is would probably be the first problem)

I will be drylining all the other walls in the house .....

[brugnospamsia]

Both are suspended floors. Looks like I'll be insulating the downstairs floor and improving the ventilation under it. Since the upstairs floor will be a warm / moist environment, I will either have to continue the air channel / insulation through the floor between the joists or have seperate vents through the wall upstairs.(may have to be the latter - especially as the joists run front to back and I'm quite likely to be replacing one of the upstairs floors and using wallplates and hangers )

No doubt there will be horrendous temperature differential cracking if I don't insulate the wall under the upstairs floor ....)

It's a pity the kitchen is not being done for a bit as I have broken all the rules there. It is the most exposed part of the house with every kind of wall construction (but plastered) - all battenened with 1 inch of expanded polystyrene slab crammed in, then leaky ply wallboards so I will see if all this palarver is really neccessary :-)

[brugnospamsia]

unfortunately not - it's a centre-valley :

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