Rockwool or celotex

If you want to be Eco friendly, look at HEMP or even Wool. I have used both and they advantage is there is little to irritate your skin when installing when compared to Rockwool and easier to cut/size than Celotex.

100mm of Celotex is a lot! My cavity walls only use 80mm and that was considered high but needed because of neighbouring glazed walls. If you do stick with it, then go for 2x40mm - remember 4x2 is under 100mm - normally 95 or so and Celotex will not compress. Cutting accuracy is then not as vital, go for 3-5 mm under width and use small wedges to force the first layer to the left then the second to the right. Yes, a small amount has less than full thickness but there is no route for cold air to flow.

 

Rockwool is better in fire - less toxic gases

 

But it is horrid to work with.

 

Celotex doesn't burn so no fumes.

 

90mm Celotex or equivalent will give the best insulation, it's insulation factor is about twice that of Rockwool. But it needs cutting which takes time and is messy. Rockwool might be easier to install, although you have to keep it in place somehow and if installed vertically ain't so simple. Its also cheaper.

Horses for courses. If the studwork is new, it should be straight which makes cutting celotex to fit a lot easier.

 

100mm is a lot.

 

It does, smokes like beach too

 

I've had plans for a garage conversion back, and you may say that's a lot, I've been told to use 110mm Celotex in the exterior wall!
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I find Celotex easier to work-with personally, purely because of i think its easier to install on your own, it makes a mess cutting, but isn't irritant to skin and you don't have to worry so much about small particles in the air.

 

It does phil, I have thrown it on many a bonfire and when the fire is done there is no celotex, so it either got up and walked away or it burnt.
Can only put it on in little bits as it smokes that much

 

The stuff I tried burning wouldn't, so it must have been a special type.

 

Cellotex is based on polyisocyanurate - an organic polymer. In its virgin state it will ignite and burn very easily. That is why all these plastic foams have to have fire retardent added to them.
First problem: fire retardent will only prevent easy ignition and slow down the burning rate but given enough heat (e.g. a bonfire and not a match) it will burn. Second problem:because the fire retardants tend to be toxic chemicals and/or make toxic chemicals when heated, these end up in the smoke.
Third problem: because the fire retarded material burns very inefficiently (after all that's what the FR treament is for) this unfortunatley makes a lot more smoke than if you just burned the virgin plastic.
With rockwool, this is 92% stone - by definition non-combustible. But it does have 8% resin binder which can fume when heated.

diymostthings

 

I use a lot of fire retardant materials and the deal is roughly that it will ignite if heat is applied but it will extinguish itself if the heat source is taken away.

 

Whatever insulation you use, staple a DPM over before boarding...

 

Celotex has the best thermal performance and it will not slip down with gravity, as above, don't forget the vapour barrier.

 

100mm really is a lot. I did 25mm on my single brick walls and the rooms are as warm as my insulated cavity walled rooms in the rest of the house.

 

Yes. Complete overkill.

But it may be that Azas has been given no option?

In any case, the daft old conundrum exists - Azas plans to build a 4"-thick frame in from the wall which will 'hold' the 4" of insulation? What will the final insulation value of some of this new wall be? Yes, that of 4" of timber.

Now, I guess 4" of softwood is darned good insulation, but how does it compare with 4" of Celotex? I don't know, but if it's less than the same thickness of Celotex, then this strikes me as compete nuts.

AND, unless he cuts that Celotex to fit PERFECTLY in between the timbers, then he'll have cold spots - that's very bad news.

When insulating walls or ceilings or whatevs, surely the main criteria is to have an even and unbroken level of insulation throughout?

What would I do to insulate a solid wall? What I have done in the past - vapour barrier the wall. Attach timber frame to wall (or floating is preferred) but no more than 2" thick - anything else is literally a waste of space. Infill with Jablite (cheap, expanded foam insulation), and then overboard the whole thing with 35mm insulated board (or thicker if you wish).

(Or, in Azas's case, pin on a 1" (or so) layer of Celotex, taping the joints, and then overboard with your Wadi board.)

That's what I did in a 4" thick single-skinned attached garage to turn it in to the room I am currently sitting in - a multi-function room. I can honestly say it's the cosiest room in the house and the easiest to heat - even in winter it is kept warm by the heat from the PC...

However, there are Building Regs, so perhaps Azas' hands are tied? But, if 4" of Celotex or any other insulation must be used, don't have it framed by 4" timbers - have it as a separate cover-all layer.

If he can get away with it, in his case I would do as I've done before except to use 2x2 timbers to strap the wall, infill with Jabbie and then overboard with whatever thickness of insul p'board he wants - but no more than 2" thick 'cos anything over this is as pointless as a pointless thing.

(My strapping was only 1" thick - I used tanalised roofing battens! 1" Jablite and overboarded with the thinnest insul board I could get - 25mm insul with 9.5mm board. Although the room is around 20-odd feet long, it is only about 8' wide, so my main consideration was to not reduce width. But, it is GENUINELY cosy.)

Adding an extra inch to an insulation layer does not double its effectiveness - it only improves it by a tiny fraction. Why? Because the 'first' inch has done most of the work - reducing heat transfer down by a huge %-age - so the 'second' inch can only hold back a tiny fraction of the tiny fraction that got through the first inch...

 

My partner reckons an extra inch makes a heck of a difference

To DA's point, doubling the insulation does not double the insulation value.

If the R value is 2, U value is 1/2.

Double the insulation (twice the cost) so R value is 4, U value is 1/4 or 0.25. Its half as good again, 50% improvement over the above at double the cost.

Double it again (4 times the cost), R value is 8, U value is 1/8 or 0.125. I think that means its 75% improvement over the first option at 4 times the cost.

 

Is 50 mm of celotex is enough to convert my garage into a living place ?

so
45x70x2400 timber
50mm Celotex
12.5mm Plasterboard
With 7.5 mm air gap between Celotex and Plasterboard