Rigid Insulating Materials, What are rigid insulating materials

Rigid insulating materials speaks to what is rigid insulating materials used for low slope roofs should have high thermal resistance, adequate resistance to compression, denting, gouging, moisture decay and fire. If the roof is part of a hot applied system it is required to have high resistance to melting or dissolving when hot bitumens are applied to it by mop.

No single material has all these required properties and sometimes a combination of materials is required.

Below listed are materials used with stated R value, composition stating advantages and disadvantages.

Cellulose fibre board R is 2.8

It is a rigid, low density board of wood or vegetable fibers with a binder, which may be coated or impregnated with asphalt.

Advantages are, it is economical and compatible with hot bitumens.

Disadvantages are, it has lower insulating efficiency than plastic foams, susceptible to absorption of moisture and decay.

Perlite board R is 2.8

The board consists of granules of expanded volcanic glass and a binder pressed into a rigid board.

Advantages are, it is an inert material, fire resistant, compatible with hot bitumens and is dimensionally stable.

Disadvantage is it has a much lower insulating efficiency than plastic foams.

Cellular glass board R is 2.9

The board is rigid, low density board of heat fused, closed glass cells with kraft paper facers.

Advantages are, it is an inert material, fire resistant, compatible with hot bitumens and is dimensionally stable.

Disadvantage is it has a lower insulating efficiency than plastic foams.

Mineral fiber board R is 4

It is a rigid, low density board of rock, slag or glass fibers and binder, usually with glass fiber mat facers.

Advantages are, it is an inert, fire resistant, dimensionally stable and compatible with hot bitumens and ventilates moisture freely.

Expanded polystyrene foam board (EPS) R is 3.6 to 4.2

It is a closed cell rigid foam of polystyrene plastic manufactured through a molding process.

Advantages are less expensive than extruded polystyrene foam, compatible with asphalt at low temperatures.

Disadvantages are it is combustible, high coefficient of thermal expansion, greater moisture absorption than extruded polystyrene foam, not compatible with hot bitumens.

Extruded polystyrene foam board (XPS) R is 5

It is a closed cell rigid foam of polystyrene plastic manufactured through an extrusion process.

Advantages are resistant to moisture, suitable for protected membrane roof systems, compatible with asphalt at low temperatures, available in high densities suitable for roofs subject to traffic loads or heavy overburdens.

Disadvantages are they are combustible, high coefficient of thermal expansion, not compatible with hot bitumens.

Polyisocyanurate foam board R = 5.6

It is a closed cell rigid foam of Polyisocyanurate with facings of aluminum foil, glass fiber mats or cellulosic mats.

Advantages are high insulating efficiency, compatible with hot bitumens and moderate fire resisitance.

Disadvantages are, expensive and rated R value may decrease over time.

Composite insulating boards R varies

It is sandwich layers of foam plastic and other materials such as perlite board, mineral fiber board and saturated felt.

Advantages are you can combine the high insulating efficiency and moisture resistance of foam plastics with the fire resistance, structural rigidity and bitumen compatability of other materials.

Lightweight insulating concrete R = 1 to 1.5

It is concrete made from lightweight material, perlite or vermiculite or foaming air entraining agents.

Advantages are it is inert, can easily produce a tapered insulation layer for positive roof drainage, fire resistant, dimensionally stable, often combined with imbedded foam plastic insulation to achieve higher insulating efficiency.

Disadvantages are residual moisture from mixing water can cause blistering of the membrane.

Rigid Insulating Materials

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