Dear GBF,

I am insulating the loft space to convert it into a warm attic. I am thinking what to do with the chimney breast in the loft. It has three flues, of which one is working (wood burner in occasional use, with a steel liner, vermiculate around it). The chimney breast is channeling the cold from the roof bit and from the neighbour's loft, which is cold. Hence it seems natural to insulate the chimney breast. However, the question is:

how to insulate the chimney breast in the loft?

I believe that one could use normal insulation board like e.g. Celotex GX4100, since the flue is insulated inside the chimney breast, but since we are talking about a wood burner, I would like to hear some opinions if this would be a safe thing to do?

Many thanks!

As far as I could see Kingspan Greenguard GG300 is XPS which is flamable
quote
Much like the EPS, the XPS insulation degrades under direct sunlight and is flammable.
End quote.
What I did see from Kingspan is the performance of Insulated panels which to me implies (and the photo looks like) cladding panels i.e. insulation covered with something. Of course I might be wrong in these assumptions.

I would be inclined to use Rockwool batts to insulate the chimney breast.

Will the loft space be a habitable space ?

Quote:

"Does GG300 meet fire safety standards? Yes, each GG300 product is meticulously crafted to meet and exceed the required fire performance standards for its intended application, ensuring the safety of your building."


A classic example of carefully worded marketing BS.

'Application' is the keyword. Used as part of a carefully specified system it can meet fire regs requirements. The fireproofing aspect will actually be provided by the exterior finishes as part of an REI 30 or greater build-up.

This relies on correct installation and specification - if the fire gets through the outer layers this will go up like a candle as happened at Grenfell. Given that this is Kingspan we are talking about, I'd want to check that the fire performance they advertise is not for a product that they stopped making 5 years previously...

As an example, we sell woodfibre insulation that has a fire classification of E. Behind a render system this achieves a B-s1,d0 classification. This is a classification of the render system, not the woodfibre; depending on which system is used the render manufacturer can provide the relevant data.

We also offer specified build-ups to meet REI 30 to 190 (denoting minutes of resistance to fire) but in all cases, this will depend upon the internal and external finishes.

As an aside, unlike synthetic insulations, the smoke produced from natural insulations like woodfibre does not contain the carcinogens, cyanide, and other nasties released in typical house fires.

You don't want XPS or PIR anywhere fire might be a risk. The fact that it goes up like a Roman Candle is only the most obvious risk - the long-term health issues from breathing in poisonous smoke is a more insidious risk that our firefighters can attest to.

I had a small chimney fire in my Edwardian house. 6" of brickwork and lime mortar behind an inch of lime plaster. Theoretically, a very high fire resistance. Empirical testing proved otherwise...

Having experienced two house fires I will never take risks to save a few quid.

Rockwool for me in this application. Natural insulation wherever else is practicable.

Call me risk-adverse - waking up in a smoke-filled room at 2am with the Fire Brigade banging your door down will do that to you :-)

The risk - albeit incredibly small - is not the temperature from the WBS flue during normal operation, but the chance of a chimney fire, which is a different lump of cheese entirely...

Timber takes a while to properly ignite. Flammable insulation takes seconds. In my case, the previous owner had stuck polystyrene tiles to the bedroom walls and ceilings. These went 'woof' along with the fake 'Victorian' plastic fireplace, but the ceiling timbers and bedroom door were barely touched.

We have a responsibility to build with thought for the next owners of the property. They might remove the flue and opt for an open fire at Christmas. Or they might reinstate one of the other unused flues.

You can't mandate for stupid, but you can mitigate it.

The cost of insulating this small area with mineral insulation is tiny <£60.

Agree