insulating a room

Hi,
I'm finally getting around to insulating our north-facing bedrooms. Not only are they north facing but for some reason that side of the house has been built with breeze blocks on the inside and tiled cladding on the outside. The other three walls are breeze block/insulated cavity/brick and so the rest of the house is much warmer.
The advice on this group was to fix 50mm celotex to the north wall. Should I fit the celotex and battens to the wall as it is or should I chisel off all of the plaster back to the breeze block? Behind the top coat of plaster there is half an inch of very sandy plaster that I am sure would come off very easily. Leaving the plaster alone would save time and mess. OTOH I am going to loose a few inches of the room when I fit the celotex and plasterboard, so by removing some plaster, this would minimise (very slightly) the loss. What would you do?
One room is quite small and has a big window. Since there is almost as much window as wall, will the celotex make much difference or is most of the heat loss occurring through the glass?
TIA
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On Fri, 02 Apr 2010 08:28:48 +0100
What would you do?
Knock the plaster off with an SDS chisel, but not take much care except where the batten will sit.

The U-value of a single-glazed window is about 5. For double glazed that drops to about 2 (2.9 for minimal DG, and 1.7 for argon-filled k-glass, IRC).
For the walls, 3" single brick is 2.2, 11" cavity is 1.
Quinn Therm (like Celotex) is 25mm 0.95, 60mm 0.38, 100mm 0.22.
The math is easy, Area x U-value x Temperature difference = loss
So, lets say your wall is 4metres long at 2metres high with a 2mx1m window in it. That's 2 sqm window and 6 sqm wall. Assume the outside temp is -1C, and you keep the inside at 18, the temp diff is 19.
Before you start: loss is (6 x 2.2)+(2 x 5) = 23.2 After you finish: loss is (6 x 2.2 x 0.38) + (2 x 5) = 15.016 But if you DG too: loss is (6 x 2.2 x 0.38) + (2 x 1.7) = 8.416
If I got that wrong someone will be along later...
R.
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Solid insulation tends not to give a great ROI, but with a 4" wall it shouldbe well worth it. If it avoids needing to upgrade heating, or is done when replastering is needed anyway then it pays back better. I wouldnt worry about removing plaster, unless for some reason youre desperate to have that inch or 2.
Generally I'd also ask myself what else can I do that will save time later. I'd be looking at the possibility of running 2.5T&E round at socket height so sockets can be added anywhere later, and getting in some cat5es and coax.
NT
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wrote:

The inverse of U-values are added when insulation is placed in series, so U-value for cavity + 60mm celotex would be 0.32
1 1 1 __ + ___ = ___ 2.2 0.38 0.32
Or am I the one who's wrong?
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On Fri, 2 Apr 2010 17:22:09 +0100

and I forgot to multiply by the temperature difference. (My spreadsheet is OK, but my explanation.....
R.
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Fred wrote:

those infra red temperature measuring guns are good, I found the coldest bit was the top foot of the wall, where it joins the roof its very thin.
There's heatloss through 4 walls, the floor and ceiling. If theyre internal walls they probably dont matter, as any heat flow would still be within your house.
and would the extra 2 inches of plaster make the window cill look better from the inside?
Secondary glazing is easier than replacing the whole window.
[g]
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Fred wrote:

Surely that's a straighforward question only you can answer: you know how much "room volume" you'll lose by leaving the plaster in place; and I'm sure you also know how mucg aggro it will create to remove said plaster - is the extra room volume worth the aggro to you?
I suppose it also depends on the size of the room: if it's a ballroom you're never going to notice a half-inch thicker wall; whereas if it's a tiny, compact study in which evry inch counts, then you probably will notice.
David
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If any wall is single skin &/or solid construction then damp may be an issue. In which case it can be worth painting the inside with SBR (available from Screwfix, B&Q) - you will soon know if there is any damp penetration once you remove the plaster (hard or damp mushy underneath the wallpaper, particularly if vinyl).
A vapour barrier is still important to prevent interstitial condensation between insulation & wall, that can be handled by the barrier on the insulation itself and using treated wood battens.

Removing plaster regains room space that would otherwise be lost, it can be worth 16-20mm or more. Plaster is vulnerable to "blowing" once encased in insulation with solid brick construction. If you screw battens to plaster the battens can become loose over time as plaster disintegrates, particularly if you have a skim over all-sand-no-cement browning).
Ideally empty the room, tape dust sheet to skirting, masking tape the door completely. Realise you will need to remove & refit skirting boards on walls that are insulated, plus deal with window reveals & internal window cill (deeper).

Sandy plaster sounds like browning, if the wall has browning under the plaster and it has blown then it will all come off in "3ft-by-2ft planks" which hold their integrity until shown a waste bag whereupon they will instantly lose all cohesion in a cloud of protest :-)

Secondary glazing - perimeter frame mitred, batten at rear, acrylic, batten at front, drawer hoop handles, closed-cell foam strip around the perimeter. Yes it takes a bit of effort to make, but done right it will work well. If frames are wooden, remove in spring to avoid moisture buildup. Plastic film works well too - remember it is the air gap that counts, 22mm beats 6mm for example. Argon fill is a humorous headline grabber because it leaks out over time relegating the fill to "conventional "air".
If you have solid double brick its U is 2.11, an insulated cavity is 0.73 for comparison so do not underestimate the thermal losses through solid walls. The same goes for having 2 outside walls vs 1 outside wall (3 walls with +18oC the other side is very different to having 2 walls with +18oC the other side & 2 walls -5oC the other side).
Single brick, if that is what you have, has huge thermal losses. Most old "bay windows" have an insulation value of 3-4mm of polystyrene at best - sticking even 12.5mm Marmox with 3mm plaster skim makes a noticeable difference to them (cold air doesn't plunge onto the floor in winter).
Basically a tiny "box-room" with 2 outside walls can save 300W going from solid-double brick to 50mm Celotex, which is 8kWhr per day energy saving through the winter or 26 gas every year or 60-90 electricity. So payback is about 3yrs on materials, the benefit of interior insulation is very rapid warmup - you do not need much heat to keep "thermal mass of bricks charged" and can instead heat on demand (very useful for rarely used box-rooms).
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I can vouch for that. My office, which is basically the rear half of the garage, has 45.5mm + 9.5mm Knauf insulation (and 50mm Rocksilk in the divider wall). At about 2.3m x 2.1m, it warms up in 5-10 minutes (with a 2.5kw oil filled electric rad), and holds the heat for several hours after the heating is switched off. Probably the cosiest room of the house now! :-)
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wrote:

[...]
Thanks for your replies. True, I would only save an inch or so at most by removing the plaster but I think this would not be too time consuming with an sds chisel. It is a small box room so I guess every bit of space I can save will help. It looks as though half of it would come off if I sneezed, so I may as well take it down before it falls down itself. Thanks again.
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[Default] On Fri, 02 Apr 2010 08:28:48 +0100, a certain chimpanzee,
wrote:

Is the concrete block leaf 100mm thick or 200mm (or greater)? Is there a structural frame to the tile hanging, or is it battened straight onto the block?

Is there any possibility of recladding the exterior? Depending on the make-up of the external wall, it may be possible to insulate between any framing members, remove & rehang the tiles with a layer of insulation against the concrete blocks, or even render the outside over external insulation.

It depends. Some modern DG units can have U-values of 1.8W/m^2K or lower, which is lower than 9" brick walls at ~2.0W/m^2K. Any improvement in the walls or the windows will reduce the overall heat loss from that room.
--
Hugo Nebula
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wrote:

I'm not sure what's under the cladding as I've never been able to remove a tile to look. Since all the tiles overlap, how do you manage to remove one to see? Smash one with a hammer?!
I did ask a builder for a quote but he never got back to me, so I presume he wasn't too eager to do it. I had asked him to put kingspan between whatever battens the tiles are fixed to but the problem was, we never knew what to put on top: we couldn't find any cladding that we liked. SWMBO didn't want timber or PVC strips and isn't keen on the tiles! The render is a possibility we never thought of, thanks, we will have to consider that.
Downstairs is not too bad: the single skin/cladding is only from the first floor to the apex, so I thought that although insulating the exterior is beyond my capabilities, perhaps I could insulate the inside.
Thanks again.
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A builder recently told me that it was a good idea to remove the plaster. His reasoning was that, although messy, it doesn't take much time and it gives you a nice solid wall to work from, whereas plaster behind the insulation could start to crumble over time. He wasn't trying to sell his services but talking about me doing it while he was doing another job on the place. I suggested taking the plaster off just where the battens would go, but he didn't think it was worth trying to do that. I still haven't decided how to do mine, but I suspect that he's right, and based on a lot of experience. Of course, as a builder, he doesn't have to clean the place up after he's finished.....
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On 5 Jan,

I got the plaster off the kitchen walls very easily by hiring a kango hammer fo a day. Very pleasing it was too, the main object being to rid the kitchen of the horrid sh*t brown tiles.
Cleanup wasn't too bad, certainly less messy than the A***e G*****r.
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Thanks. Can I ask why you hired a hammer? Was it that you could fit a wider chisel. I only ask because I always thought of these as being high powered machines for demolition, so I always associated them with removing the whole wall, rather than just the plaster! Was it heavy? I was hoping to get away with using an sds drill.
I also note AG's remarks in another reply about making sure I don't knock too much wall off with the plaster. If I said half brick wall in the OP I may have given the wrong impression. The wall is made of one breeze block, not one brick. I believed that a wall of one course is called half brick; if anyone was worried my wall was only 11cm thick then I apologise for misleading people; I should have said half block, not half brick, sorry.
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Fred wrote:

i hired one years ago to strip plaster..
LOADS of fun but it cut grooves up the brickwork a bit.

Still not sure what you have there either material wise or thickness..
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On Thu, 05 Jan 2012 20:22:15 +0000, The Natural Philosopher
By the sounds of it, it is very similar to Andrew's house. The first floor has a wall made of breeze block; I know there are different types of breeze block but I don't know how to tell the difference, so I can't say which. On the outside there is cladding made of tiles.
The rest of the house has a breeze block inside wall and a red brick outside wall with insulated cavity.
As other replies have said, rendering over insulation might be the best option for me but I would have to look into what would happen around the windows, as their sills might become recessed inside the insulation.
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Can you ask local building control?
When my wife was exploring the practicalities of cavity insulation for her flat, I was able to view the drawings (microfiche) held by the BC office. This was for a block of flats built in the '60's!

Opportunity/excuse for new windows?
regards
--
Tim Lamb

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On Wed, 11 Jan 2012 08:36:52 +0000, Tim Lamb

Will ask about this, thanks.

Yes, I've thought that too.
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On 05/01/2012 19:29, Fred wrote:

The construction is brick/block with 65 mm cavity up to the top of the downstairs window/front door, then a lintel, which in the case of my 76 semi looks like an RSJ and is infilled each side with brick (so maximizing the heat loss :-( ), then a row of bricks laid horizontally bridging the cavity, then 9 inch blocks, probably hollow ones up the bedrooms then a 4*2 wallplate carrying the trusses. The problem is the row of bricks under the blocks is just below ceiling level downstairs so you have a massive thermal bridge here running the whole width of the house. You meed to consider doing the same exercise downstairs too (as I have), and don't forget the outside wall in the void between the GF ceilng and floor - another source of airleakage in 70's houses.
I would post some photos if I could think of a way to do it.
Andrew
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