A 'is this sane' house insulation question.

[Ian Stirling]

I have a 1300s or so Scottish farm cottage.

50-60cm stone walls. At some point in the last few decades, it's been plasterboarded 50mm over the stone, but not insulated. Attic insulation has been put in, to a depth of 100mm, then boarded over.

An average of some 3Kw departs through the walls over the year.

With rising energy prices, this is a bad thing.

So. I've bought 50mm kingspan - for going round the windows, and 100mm rockwool, for going up the walls, plasterboard to go over all of this.

Some tests I did with the rockwool indicate it's fine for this - can be hung fairly staightforwardly from a bit of timber folded over some at the top, and doesn't show any signs of tearing.

Behind the rockwool, will be a 1-2cm gap from the stone, and then landscaping fabric - porous polypropylene sacking type material, stapled to the existing wood. (I happen to have a large roll)

At the base of the wall, this looks like:

W FRRRP W FRRRP W FRRRPS W KKP|S W KKP|S W KKP|S

R = rockwool P = plasterboard, K = kingspan, S = skirting board, F=fabric, W = wall |= 2mm steel (that I also have enough lying around of.)

The cavity behind the plasterboard contains metal conduit for network/ power/foo.

Also, there are every few meters small fans that draw air from under the (suspended, ventilated) floor and blow it up the walls.

To keep the insulation nice and dry. I know the proper solution is airbricks, but basically, that's not going to happen, it's a nightmare (50cm stone walls)

The fans turn on once a day at midday for half an hour or so (or possibly when something detects that the humidity is the lowest it's been in 24 hours, I'm unsure)

The skirting board/plasterboard/metal sandwitch can be unscrewed easily in sections, to allow for easy access to electrics/network cables.

I'd hope for the insulation to hit 0.4W/m^2/K, for a total over 110m^2 of walls of maybe 400W at 10C difference - compared to the current 3Kw or so.

I'm expanding the existing 50mm wood against the stone not with solid wood, but with 15mm wood the same width as the existing, but installed on frequent 35mm blocks glued+screwed to the original wood, with kingspan in the gaps.

This doesn't of course do that much for the insulation - but I have lots of 15mm thick wood suitable, but no 60, and it helps a fair bit.

Any comments?

I know that this isn't ideal, it's very much a low budget solution. An expensive one simply can't be done.

And going below 400W isn't really needed - once the windows are fixed, the total heating needed drops to around a kilowatt or so, most of which will be doable from solar gain and waste heat.

At 700 quid for 110m^2, it's not horribly bad, and should pay back in under 3 years.

[Peter Parry]

Have a look at Actis Tri-Iso

is meant for roofs but might be useful in your application and has a uValue of 0.19 W/m2/K. It is also vapour resistant.

[Ian Stirling]

Ok. Of the two working links - one gives a price. I find it rather surprising that it doesn't actually say that 189 pounds buys you 10 or 20 square meters.

This is between 9 and 4.5 times more expensive than rockwool - and I did mention that I'm on a budget...

Neglecting this.

The pages constantly say 'this insulation value can't be measured in conventional tests', and give testimonials to another test methodology.

At the very least, I want to have actual details of this test methodology, not just an unattributed statement saying that it is good.

The product has an R value of 0.6 (without cavity) as mentioned on the other working link, for a U value of 1.66 - and therefore .055 W/m/K conductance, assuming it's 33mm thick.

I'd want a damn good reason why this is better than a 33mm thick sheet of polystyrene, with foil on each side, which comes in at maybe 3 pounds per square meter, compared to the 19/9 pounds a square meter.

Or even 30mm of rockwool, and foil on each side which may end up at an even lower price.

[Tony Bryer]

a a report that suggests that the TRADA tests are not valid.

[meow2222]

Cardboard is probably one of the cheapest insulators. It traps air, and is free in quantity if you walk round any town at bin time. I know you've got the budget for rockwool, but was just wondering whether some hybrid solution could get you more result for less money. Since cardboard is not moisture resistant in any way, that limits how and where it can go.

NT

[Ian Stirling]

Well. There is a slight tradeoff between cost and space. If it wasn't actually as good as rockwool, I'd need more space. At the moment, rockwool means that I lose about 6cm - which adds up to around 3% loss of space. Cardboard would make this worse AIUI.

If I was _really_ on the pennies - and 700 quid was unaffordable, I'd still be going with rockwool, but probably 50mm, topped with the existing plasterboard.

This is only about 150 quid. Payback would be in a winter.

Or maybe even simply remove bottom 5" of existing plasterboard, seal properly to wall, and pour in lots of polystyrene bean-bag filling from holes drilled in the wall, following up with wallpapering with foil, skimming. A fair bit less work, but more expensive than the previous solution.

Unless of course I went round skips for polystyrene, and chipped them to get particles to pour in.

[AJH]

Isn't this the one that the asa upheld a complaint against in may 2006 because their tests did not conform to any standard? This of course doesn't mean it doesn't work.

I posted about this on here when I saw it being used a year or so ago and it seemed too good to be true then someone, who for arguments sake I'll call Adam, who initially seemed enthusiastic about it tracked down this judgement and posted it on another forum.

AJH

[fluffkin]

The gap needs to be between the stone and the fabric doesn't it? 1-2cm is really pushing the limit of what's going to allow adequate ventilation. 30 to 50mm would seem more practical / installable. Rockwool is very moisture tolerant, especially if supported enough to stop it sagging.

The steel worries me. Isn't that going to condense any moisture on to your plasterboard and skirting? And the kingspan I know is a corrugated steel pre-insulated sandwhich... Is that what you mean?

Just those above...

[Ian Stirling]

Yes - 1-2cm between the stone and the fabric.

It's marginal - which is why I'm using fans to actually blow air past it from the floor void. (1/2 hour a day or so) It's more to keep the wood dry, than the rockwool. I'm going to stick in a few sensors at the same time, as that's free.

Yes, 50mm would be nice. But, that's another percent or so off the house volume... (and a number of more awkward things as I need to move doors)

[Ian Stirling]

Oops.

It's actually aluminium, and it's not corrugated, as much as 'as flat as they can get it.'

No - the steel is to protect the cables from the over-enthusiastic with drills in the future.

The metal is directly behing the skirting board, on the 'hot' side of the insulation.

The kingspan is there so that there can be enough space behind the insulation at the bottom to run cables, and have a void to blow air through, without compromising on insulation value - as it's twice as insulating as rockwool. I'd like to go all the way up with kingspan - as that would make it a hell of a lot easier - but it'd add 600 quid to the cost.

[meow2222]

Has anyone measured cardboard's insulation value? I assume youre right, bigger pores and all. It might be handy to know what its value was though.

Labour value would be murderous though. One could simply use household rubbish - plastic, paper, carrier bags, wrapping - nothing nasty. A lot of people are not doing solid wall insulation because of the cost, this sort of thing could enable more such insulation on a diy basis. Assorted cardboard boxes cut down to 2" also work, giving a 2" cavity with lots of baffles to almost stop air movement.

NT

[marvelus]

I dont think the fans would work as you hope, wouldn't it need to vent to outside at the top of the walls? Such a small gap would presumably put up quite a resistance to air movement aswell. Then how do you get access to the fans to service them?

[nafuk]

I'd try my very best to do it all with kingspan/celotex/xtratherm etc. I'm on a budget also but there are dealers on ebay etc. who sell seconds at lower prices. I also got my local builders merchant to give me some 50mm 2.4 x 1.2 m sheets delivered for =A320 inc. vat.

[Ian Stirling]

Good quality fans - I have had identical ones running for a couple of years. And the skirting board just unscrews, and you get to them easily.

I've actually found somewhere the flow resistance of a rectangular box, and computed it. It's not a problem - the flow rate is _very_ low, around 1cm/s or under.

That's the price I got at Jewsons, more or less.

Unfortunately, another 550 quid or so isn't really possible ATM. The only advantage this would have is labour saving, and space saving, not actual energy.

[Peter Parry]

No idea, I can't find anything on the ASA web site about it. The paper Tony mentioned is quoting a Um value of around 0.5 (R-value of

1.71 m2K/W). The only bit I've got is about 6in sq so not much use for measuring anything :-). The advantage in this application would be that it would replace both the insulation and vapour barrier and take up somewhat less space. However, the cost appears to rule it out.

[Ian Stirling]

The vapour barrier in this case takes no space - it's foil PVA'd onto the back of the plasterboard. (yes, I was too cheap to buy foiled plasterboard, I find that a pressure sprayer filled with diluted PVA, and kitchen foil is really fast to apply.)

[Hugo Nebula]

On 25 Oct 2006 14:22:01 GMT, a particular chimpanzee named Ian Stirling randomly hit the keyboard and produced:

You're probably losing a lot of heat through your roof.

I'm not sure what you mean. 3kW is a rate of energy transfer and only gives you a figure of how much you're losing per second. If you mean

3kWh, then this is a minuscule amount over a year.

A 600mm stone wall has a U-value of about 1.33W/m^2K; in other words,

1.33 Watts for every 1 degree (Kelvin or Celsius) difference between one side of the wall and the other. Multiply this heat loss by an average 10 degree difference over the heating season x 18 hours x 180 days (the period the heating is on) x 110m^2 (wall area) / 1000 (W to kW) gives 4,740kWh of energy lost through the walls per year.

This sounds like a bad idea. You'll be drawing up cold, damp air into the space between your insulation and your wall. It'll condense on the inside of your wall and permeate into your Rockwool.

How much Rockwool could you buy for your loft for that money? 200mm laid over your ceiling joists would reduce the fabric heat loss from

0.46W/m^2K to 0.13W/m^2K. You could put the rest between your floor joists.

[Ian Stirling]

Well - not really. There is 100mm of fibreglass in there.

Adding 100mm of fibreglass may be almost as hard as doing the plasterboard downstairs, with a tiny fraction of the payback.

However, I'm talking of an average power over the year.

It's actually fairly warm dry air. (noninsulated suspended floor) if I was to insulate the floor, then I will need to do something else.

0.46W/m62K * 80 = 36W/K = 360W at 10C difference. 0.13W/m^2K * 80 = 10W/K = 100W at 10C. So, a saving of 260W, for a hell of a lot of work - the attic is already boarded, as well as reducing quite a bit of usable space.

And maybe another 700W by doing the floor too. (not to mention the floor would involve a hell of a lot more expense and work.

Versus around 2600W by doing the walls.

Thanks for the comments. However, I believe that once I have done the walls, and the next long pole - replacement sealed units for the single pane windows (700W@10C) then the house should actually pretty much run on around 1-1.5Kw at

10C difference. Add a small 2m^2 solar thermal panel on the roof, and I think I can almost turn the heating off forever. I may not bother with this - the payoff on this is quite long.

[meow2222]

Whats your cost figure for that? Are you using a glass glazed frame with mylar film secondary layer, and 2 layers of black mesh for absorber, or something less efficient and more expensive? If you were able to put it at ground level this would reduce costs more, and you could do away with the fan. Also you surely want more than 2 m^2, quite a bit more to see you through as much winter as possible.

I'm beginning to wondering if youre talking about water heating?

NT

[Ian Stirling]

I'm not quite sure.

I suspect it may be as simple as a couple of old radiators, feeding into the heating loop, underneath a double-glazed insulated cavity in the roof. As I have most of the stuff for this, and air heating is rather more annoying to implement. (though a means of solar heating intake air is interesting.)

Yes - but not hot water heating. Rather as the radiators are now 3-4 times oversized, they should output enough to keep the place warm at 20C over ambient or so. There may well be an additional warm water store, I'm not sure.