Thermal insulation is one of the most important system components in a roof, creating a comfortable environment inside the building by protecting it from heat and cold while also helping to reduce heating and cooling energy costs. The importance of thermal insulation has increased recently mainly due to changing insulation standards worldwide, which put higher demands on the thermal resistance of building structures to reduce energy loss for heating or cooling.
Insulation types used in flat roofing systems should have not only high thermal characteristics but also sufficient mechanical properties to be able to withstand loads (e.g., snow loads, ballast, limited pedestrian traffic for maintenance, moisture in inverted roof build ups, etc.).
Common Types of Thermal Insulation Used on Roofs
Polyurethane Foam (PIR/PUR): PIR is a thermal insulation board produced in a chemical process from rigid polyurethane (PU) foam combined with an isocyanate catalyst. This is a very universal and efficient solution for all kinds of exposed roofs. It is one of the most suitable insulation types for adhered roof systems and can also be used in ballasted roof applications.
Advantages of PIR/PUR
Very good fire resistance (more than 250°C)
Extremely low thermal conductivity value of 0.023 – 0.028 W/m·K
High compressive strength in the range of 100 – 300 kPa, which is also sufficient for some ballasted applications
Lightweight in the range of 30 – 60 kg/ m3
Stone wool, also known as rock wool, is a type of mineral wool insulation produced from basalt stone fibers. It is one of the most common solutions for exposed mechanically fastened roofs, especially where very high fire resistance is required.
Advantages of Stone Wool
Excellent fire resistance (up to over 1000°C), most stone wool products are classified as noncombustible
Low thermal conductivity value of 0.038 – 0.041 W/m·K
Compressive strength in the range of 40 - 80 kPa, which is sufficient for exposed roofing applications
Weight is in the range of 100 – 200 kg/m3
Expanded Polystyrene (EPS)
EPS is a thermal insulation board produced from expanded polystyrene granules. It is one of the most cost-efficient solutions for exposed and ballasted roofing systems.
Advantages of EPS
Most of the products are self-extinguishing in fine
Low thermal conductivity value of 0.037 – 0.041 W/m·K
High compressive strength in the range of 100 – 250 kPa, which is also sufficient for some ballasted applications
Lightweight in the range of 20 – 40 kg/m3
Extruded Polystyrene (XPS)
XPS is a thermal insulation board produced from polystyrene in an extrusion process. Due to its special characteristics, it is the ideal solution for inverted ballasted systems and utility roof decks. XPS can also be used in exposed roofing systems.
Advantages of XPS
Almost zero water absorption
Most XPS products are self-extinguishing in fire
Very low thermal conductivity value of 0.034 – 0.038 W/m·K
Very high compressive strength in the range of 250 – 700 kPa which is sufficient for utility decks with high traffic
Lightweight in the range of 25 – 35 kg/m3
PIR Has Many Clear Advantages over Other Types of Thermal Insulation
Lower thickness compared to many other technologies - thinner thermal boards for same performance
Low density – ideal for renovation projects, less workmanship needed, adds minimal additional load to roof
Heat resistant up to 250 °C, does not melt, does not support spread of fire
PIR GT is “universal” (adhered, mechanically fastened, ballasted roofs)
Better compressive strength value than mineral wool
Excellent workability (does not irritate skin, easy to cut, lightweight boards are easy to transport, etc.)
Boards are available in tapered version
Compatible with PVC, LAM and most Sika roofing build-ups
Less price sensitive compared to EPS or MW
Sika plan / Sarnafil membranes can be laid directly on PIR board. Integrated facers on the boards prevent from direct contact between PVC and PIR foam
Source: Sika Group