Polyisocyanurate is one the most efficient and high performance insulation materials available for loft conversions and is becoming more and more popular with builders.
This material is most commonly supplied as foil faced rigid boards.
Supplied in a variety of thicknesses from 20mm up to 100mm and sized 2400 x 1200mm these boards can be used in both pitch and flat roofs as well as for wall insulation.
Polyisocyanurate (PIR) is one of the three most common multi-use rigid insulation boards along with phenolic foam (PF) and polyurethane (PUR) but is a more fire resistant material than its competitors.
The fire safety aspect of polyisocyanurate insulation material is hugely important for loft conversions.
With the building regulations so rigid when it comes to fire resistance the reduced combustibility of PIR makes it very attractive to planners and builders.
Although polyisocyanurate roof insulation is made in a similar way to polyurethane and, although the same elements are used in the manufacture of the two products, the higher intensity of materials used in polyisocyanurate gives it greater fire resistance and forms less smoke.
The material uses a blowing agent, often pentane, which expands the foam and enhances the thermal resistance of the insulation.
The performance of insulation material can be measure by its conductivity value.
And foil faced polyisocyanurate has the best (lowest) figure.
Typical values are:
Foil faced polyisocyanurate 0.017
Foil faced phenolic 0.021
Foil faced polyurethane 0.021
The great benefit to builders and planners in using multi-use rigid insulation boards such as foil faced polyisocyanurate is that only half the thickness is needed compared to other more traditional boards such as expanded polystyrene which has a conductivity value of 0.033.
For more info see the related pages below
So - What Is The Best Loft Insulation?
The Loose Fill Alternative To Polyisocyanurate Roof Insulation
Structural calculations for loft conversions are of course hugely important to ensure safety and that the proposed plans meet building regulations
What is the difference between planning permission and building regulations approval for loft conversions ?
Using And Fitting Loose Fill Insulation In Your Loft