When choosing the best roof insulation for flat roofs or commercial buildings, the top materials include polyiso, spray foam, and extruded and expanded polystyrene.
We’ll look at each of these materials in more detail, but first, let’s go over what to look for when choosing a flat roof insulation material.
Key Considerations When Selecting Flat Roof Insulation
When choosing the best insulation for a flat roof, here are some things to consider:
- Since they have very little slope, flat roofs are prone to standing water. Make sure you choose a moisture-resistant insulation.
- You want the most insulation value (R-value) you can get. Higher R-values indicate greater thermal resistance, reducing the need for air conditioning and heating.
- Flat roofs are prone to air drafts, so insulation that provides above average air sealing will help keep the hot and cold air where you want it.
- Effective flat roof drainage requires slightly tapering the roof surface. The right insulation can help with creating these drainage slopes when needed.
4 Top Choices for Flat Roof Insulation
The top four insulation types for flat roofs include polyisocyanurate (polyiso), spray polyurethane foam (SPF), extruded polystyrene (XPS), and expanded polystyrene (EPS).
Polyisocyanurate (polyiso)
Polyiso, one of the more popular types of roof insulation, is a rigid foam insulation board with a high R-value (up to 6.8 per square inch), good thermal performance, and moisture- and fire-resistance.
It’s best suited for commercial building flat roofs, especially those seeking high energy efficiency.
Spray polyurethane foam (SPF)
Spray foam comes in open- or closed-cell varieties, with closed-cell foam providing the best R-value (up to 6.6 per square inch). It’s applied as a liquid that then expands into a foam that creates an airtight barrier, adheres to irregular surfaces, and adds structural integrity.
SPF is best suited for sealing air gaps, on uneven surfaces, and for buildings seeking high energy efficiency.
Extruded polystyrene (XPS)
Extruded polystyrene is available as a rigid foam board, much like polyiso insulation, and is commonly used under membrane roof systems. It’s a dense, durable insulation with great compressive strength and good moisture resistance. It offers mid-range R-values (5 per square inch), balancing performance and cost.
XPS is well-suited for high-traffic areas and roofs requiring durable insulation under heavy equipment.
Expanded polystyrene (EPS)
EPS is also available in rigid foam board, is lightweight and cost-effective, and can be easily cut to create a tapered slope. It doesn’t have the best insulating value (4.6 per square inch), but its cost makes it more attractive than some of the other materials.
It’s best suited for budget-conscious projects and for creating tapered insulation systems to improve roof drainage.
Choosing the best flat roof insulation for your building
Before deciding which insulation material is best for your building, consider:
- Budget
- Energy efficiency goals
- Amount of foot traffic and equipment
- Roofing materials
- Drainage issues
Our experts are available to help you choose the best roof insulation and roofing materials for optimal protection from your system. Reach out to us to get started.