Fire questions around insulation materials

Two criteria that can clash

In choosing insulation, thermal performance is one criterion: what it achieves per unit of thickness, how it behaves with moisture, how it can be installed.

The other criterion is fire safety, and it is often the stronger constraint: where the regulation does not allow a combustible material, a better thermal figure is irrelevant.

Where the regulation sets a material class

On the facade

Strictest here, because the facade is a fire spread route. The requirement gets stricter with building height and risk class. Fire spread on the facade.

In cavities and ventilated gaps

Combustible material in a cavity burns hidden, and the chimney effect of the gap accelerates it.

Along escape routes

Where people escape, smoke production and flaming droplets are a direct danger to life.

Generally in higher risk classes

Where the classification requires it, stricter requirements may apply to materials inside the structure as well.

The practical consequence for the build-up

This is the point where fire safety directly rewrites the structure.

Where the regulation allows it, injected foam has the advantage that one trade completes both the space between the studs and the external insulation at once; it expands everywhere, so quality does not depend on how precisely gaps are filled — and for its thickness it gives the best thermal value.

Where the regulation does not allow it, mineral wool achieves just as good a result, only there careful filling of gaps is critical: a missed gap is both a thermal bridge and a moisture risk.

What must not be confused

The fact that an insulation is class A1 does not mean the structure will be fire resistant. Load-bearing capacity is decided by the heating of the section, not by the non-combustibility of the insulation. The material class of the insulation limits spread; the lining and the design provide the capacity.

The point

When choosing insulation, first look at where it goes and what the regulation allows there — and only then compare thermal figures. The other way round means redesigning the whole build-up.