Polyisocyanurate Rigid Insulation
Polyisocyanurate rigid insulation (isocyanurate or iso) is the most commonly used flat roof insulation, and can be used in any type of flat roof system. Isocyanurate rigid insulation has the highest R-value of any insulation product with an R-value of 6.0 per inch. It comes in thicknesses of ½” to 4” and can be installed in multiple layers based on your energy efficiency preferences along with building code requirements. Polyisocyanurate insulation can be used for complete re-roofing jobs, where the existing roof system is removed down to the structural deck or roof recover jobs, where the new roof is installed over the existing roof system.
Polyisocyanurate rigid insulation is known for its ability to resist water absorption, taking in less than 1%. Isocyanurate also holds up well over time, and can often remain in place for re-roofing applications where roof removal is not required, particularly over older single ply systems such as EPDM, TPO, and PVC . And, at 20 psi, it is also a fairly strong product for roofs that have typical foot traffic. For roofs with heavier foot traffic, opting to add in a layer of 100 psi ½” HD coverboard is a great way to strengthen the rigid insulation.
Benefits of Polyisocyanurate Insulation
- Highest R-Value per inch of any insulation product. (R-value – 6.0 per inch)
- Absorbs less than 1% of water, far less than any other rigid insulation.
- Relatively strong at 20 psi. For additional strength, see HD coverboard
- Holds up well and can be re-used where complete roof tear offs are not required.
- Lightweight and easy to install.
Drawbacks of Polyisocyanurate Insulation
- Cost is higher than fiberboard and eps.
Polyisocyanyrate insulation is a great product for any flat roofing application. It is a strong product that can typically be re-used in a recover roof job and it has an excellent R-value. It is also an excellent value, which is why it is the leading insulation product for flat roof systems by a large margin.