Celotex/Kingspan in a fire + fitting question

[Tim S]

Hi

[Preamble, Questions at end]

We're going to move in with my Dad next year - we're redoing bits of the dormer loft conversion of his bungalow.

Now, upon inspection, the current insulation in the roof voids is manky glass wool - yuk. Broken, falling away and very dusty.

I hate glass wool, partly as I a) have to get around the voids to fix some electrics + install networking, and b) I'm going to use the voids as supplimentary storage space for light items. I find it unpleasant and a skin irritant. I also don't want the fibers going anywhere near my baby daughter. Also, it's too knackered to be doing much good.

I also want to insulate the roof, not the floor as I want the voids to run warm to protect the stuff I'm storing.

So I thought about using either Celotex/Kingspan to 50mm, leaving 50mm breathing space in the rafters under the tiles - or rockwool slabs.

Rockwool in slab form is possibly less disgusting than glass wool

- at least once fitted (anyone care to comment?) but I believe from reading around I'll get better insulation with Celotex or it's like at

50mm. [Questions]

a) What's celotex like to cut - use a knife or a saw?

b) In a fire, does it pose any risk of giving off noxious fumes?

c) Does having an endothermic but still combustible material like celotex packed around electric cables bother you?

Thanking you kindly :-)

Timbo

[Owain]

"Tim S" wrote | c) Does having an endothermic but still combustible material | like celotex packed around electric cables bother you?

The electric cables will have to be derated for running within insulation. Lighting cables on a 6A MCB are probably already fairly generously sized, but 2.5 ring circuit cables willl almost certainly require replacing with

4mm or worse (bigger).

Owain

[Michael McNeil]

A read knife will do or the back of a saw ie any old thing.

It is widely used in this country which has very high safety regs. But not trusting anything too carelessly will stand you in good stead.

I would say electric cables are the more hazardous. "They" are still telling porkies about radio masts. Radio is just the static produced from electric circuits.

We are doomed. We're doooooooooomed!

[David Hemmings]

Knife should be quite sufficient, and it will leave the foil at the edge of the cut intact.

OOOhh yes, thick black acrid smoke. But, and i must stress this it did take quite a hot fire about 20-30 seconds to get it to ignite.

Do you really mean endothermic ?

An insulator i presume, i would try to avoid if it if possible, don't what ever you do cover up anything akin to halogen spots though.....

[Andrew Gabriel]

I found a serrared breadknife was ideal.

I recognise the smell of cyanide componds (probably used to foam it) when cutting it, so I would assume it gives off cyanide when heated. Personally, I would not use it without a plasterboard barrier between it and the house occupents. I tried lighting a thin slither offcut and it burned. Others have said larger pieces don't burn so well.

Not if adiqately derated. I would not personally let PVC cables come into contact with the expanded material incase there's any long term degredation, not that I know of any. Where I've used cable near Kingspan, I put it in PVC conduit, but that was more for ease of rethreading cables if I wanted to chance the wiring plan.

[G&M]

I have done same with Celotex - roof and walls behind plasterboard. It insulates superbly (though you need a bit more than 50mm to meet latest building regs if you have to) but it is a doddle to fit. Yes it does give off fumes when ignited but does not sustain the flame on its own so it's as safe as most other materials in the house.

If it isn't a new build contact "Seconds and Co" (use google) who supply rejects - usually a mm or two too thin but a lot cheaper.

[IMM]

Have from the inside: plasterboard and a vapour barrier under. between the vapour barrier and the rafters have a layer of Celotex. Between the rafter have Celotex. Between the Celotex and the tiles/felt have a 25mm ventilation gap. This arrangement must continue down to the eves, so air can enter the ventilation gap, but not into the loft space.

Have the internal plaster, VB and insulation form a flat section at the top of the loft, leaving a triangular section inside the loft at the apex. Then, if two gable walls, install a vent in each gable at each end of the triangular section. Then air from the eaves rises up the between the rafters, enters the triangular section out via the ends through the gable vents. If no gable ends then have ridge tile vents.

Have the loft "sealed" from air ingress via the ventilation. A highly insulated loft should result, without any fear of condensation occurring anywhere.

[Tim S]

Fortunately Building Regs don't matter here - the Seconds and Co is a useful tip - I'll check them out. At 30 quid a sheet, Celotex is normally an expensive option.

Cheers

Tim

[Andy Hall]

You can get 50mm from a builder's merchant for £15-18 if you squeeze them a bit....

.andy

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[Tim S]

That sounds easy :-)

I am thinking of a thin plasterboard finish, even in the loft. My thinking is, if it doesn't give out fumes until a fire is well established, that's good enough, because I'll be toast by then anyway. For my daughter's and wife's benefit, I'll probably put in a good interlinked fire alarm system too, including smoke detectors in the voids.

endothermic but still combustible material like

Fortunately, electrics are my strong point, and all the buried cables will be lighting. The rest will go on cable trays on the surface. The loft void is continuous around the permimeter, which is a dream for routing cables and pipes.

Many thanks

Timbo

[Tim S]

Many thanks to everyone for comments. Celeotex sounds OK so I'll probably go for it.

Cheers

Timbo

[Andy Hall]

That's curious. considering that it consists of polyisocyanurate foam and aluminium foil.

I think that you might be thinking of something else.....

.andy

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[tom patton]

If you are planning to board the roof with Cellotex--do nt plan to stay in the house!!. I own a 1970s bungalow boarded in Cellotex--its a disaster!!. Water plus cardboard--tears at bedtime!.