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 isocyanurate 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.
Stone Wool
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.
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.
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 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
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
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
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
Comparison of Typical Thermal Insulation Types
| Features | Sikatherm PIR AL/GT | Mineral Wool | EPS |
|---|---|---|---|
| Excellent thermal performance (1) | ✓ | ||
| Resistant to high temperature (≥ 200° C) (2) | ✓ | ✓ | |
| High compression strength (≥ 100 kPa) | ✓ | ✓ | |
| Low water absorption capacity (≤ 10%) | ✓ | ✓ | |
| Lightweight (3) | ✓ | ✓ | |
| Closed cell foam structure | ✓ | ✓ | |
| Direct contact allowed to PVC single-ply membrane | ✓ | ✓ | |
| Suitable for adhered roof systems | ✓ | ✓ | |
| Suitable for ballasted roof systems | ✓ | ✓ | |
| Suitable for green roof systems | ✓ | ✓ | |
| Suitable for use with liquid-applied membranes (LAM) (4) | ✓ | ||
| Insulation boards with rebated edges | ✓ | ✓ | |
| Resistance to warm bitumen | ✓ | ✓ | |
| Resistant to fungal growth | ✓ | ✓ | |
| Non-fibrous material (does not irritate the skin and cannot cause lung disease) | ✓ | ✓ |
NOTES: (1) Thermal conductivity value minimum 0.028 W/m·K (2) Short time resistance (3) Less than 60 kg/m3 (4) Only Sikatherm PIR GT allowed