On 18/06/2017 12:25, Robin wrote:
On 18/06/2017 11:55, Andy Burns wrote:
The Natural Philosopher wrote:

Get some and put a blowtorch to it.
Celotex insulation does not really burn.

Where "not really" means that an external flame will make it burn,
giving off a surprising amount of smoke, it will char and and the
flame from the foam will sputter out after a few seconds when you take
the blowtorch away ... maybe a big slab with lower surface:volume
ratio performs better than tests on offcuts of an inch or two?

I think the problem here is that when it is in forced ventilation and
exposed to a massive radiant energy as it was on the side of the
building all bets are off. It did survive remarkably well considering
but it almost certainly added to the fuel load since in extremis it will
burn/char (but plenty of charred bits remained on the building and had
fallen to the ground where they went out).

Celotex or Celotex FR5000? The former is Class 1, the latter Class 0.

When I fitted Celotex in the loft here I reckoned that by the time a
fire had gone through the plasterboard into the loft I'd either be out
or dead. And that the Victorian rafters and joists would go up like the
proverbial in any event.

Actually the heavy Victorian beams don't go up all that easily. It takes
a lot of heat and time to get a 12x4 joist to catch light. It burns the
corners off first and if the heat source is removed goes out again.

One reason for having some rodent control in lofts is they like to
nibble the insulation off mains cables.

--
Regards,
Martin Brown