Currently, there exists three principal categories of roof insulation, Fibrous, Plastic and Composite.
Rigid fibre insulation is produced from organic or inorganic material. All Fibrous insulators rely on the air film around each fibre and other trapped air to resist heat flow. This characteristic enables them to maintain the same ‘R’ value over a long term.
Fibrous Rigid Insulation:
Wood-Fibreboard is made from wood pulp and recycled paper fibres bound with resin. Although strong and stable, its ‘R’ value and moisture resistance is low. It is ideally suited as a protection overlay over plastic insulation or tapered to provide positive drainage.
Although relatively new to North America, Mineral Fibre (Rock-wool) inorganic fibre insulation is prolific in many parts of Europe. Environmentally friendly, Mineral Fibre melts a 50/50 mix of basalt rock and slag from the steel mills that would normally end up in a landfill. Spun into various densities, the wool is treated with an oil and synthetic binders. Its features include a stable ‘R’ value, dimensional stability, moisture resistance and unsurpassed fire and flame spread resistance.
Plastic Foam Insulation:
Foamed Plastics insulation on the other hand, rely on their cell structure to trap air or gas (blowing agents) to resist heat flow. Plastic insulations have the great advantage of low weight and high thermal resistance, which means thinner insulation requirements.
Expanded Polystyrene uses steam to expand beads of styrene filled with an agent called Pantene. Most of the Pantene gas dissipates shortly after manufacturing, leaving cells filled with air. With a melting point as low as 75 C degrees, use of hot asphalt and solvent based adhesives is not possible and consideration must be given to its fixation.
Extruded Polystyrene rely on a blowing agent for heat resistance resulting in improved thermal resistance. This plastic insulator has higher compressive strength and greater impermeability to water, making it ideally suited for exposed applications such as an inverted or ‘protected membrane roof’ assembly.
Increasingly popular, is the use of Polyisocyanurate foam insulation (Polyiso). This rigid board from the urethane family, also relies on a blowing agent, ranking it highest in thermal resistance. Factory applied facers add strength and a receptive surface for hot bitumen or mechanical fasteners. Tapered panels are also made to several standard slopes for positive drainage applications.
Composite Roof Insulation:
The combination of two different materials or Fibrous with a Plastic foam insulation provides a finished composite board in a quality controlled factory environment ready for installation on the roof. Most plastic foam require the protection of an overlay fibrous board such as WoodFibreboard. By factory laminating the Woodfibreboard to Expanded polystyrene (EPS) or Polyiso, the roofing contractor can apply the membrane directly to the composite board, eliminating any field lamination. Composites provide dimensional stability, strength and rigidity, protection from out-gassing, hot asphalt or torching within factory quality tolerances.
A new entrant to the Canadian market is Perlite insulation. Made from expanded volcanic glass and paper fibre, it provides a modest ‘R’ value, dimensional stability and fire resistance.
EPS + woodfibreboard dimensional stability; protection from heat; traffic
(butt edge or shiplap) resistance
EPS + Asphalt Prot’n brd. dimensional stability; protection from heat; traffic resistance;
(butt edge or shiplap) receptive surface for all types of membrane applications
EPS + Perlite dimensional stability; protection from heat & fire;
Mineral Fibre + Polyiso protection from heat & fire
(butt edge or shiplap)