Rigid Insulation Board

Rigid insulation board (Figure 3-5) is a rigid or semirigid synthetic product commonly referred to as structural insulating boards (SIP)

Rigid Insulation Board

Figure 3-5 Rigid insulation board.

Or panels, rigid boards, foam insulation boards, rigid foam insula­tions, slab insulation, or sheathing boards. They are produced under a wide variety of trade names. Rigid insulation boards or panels are commonly manufactured in 2′ X 4′, 4′ X 4′, and

4 ‘ X 8’ sheet sizes with thicknesses of V2", 3/4", and 1" nonlami­nated and laminates of V2", 1", and 2". All edges are butted. Rigid insulation boards are available faced or unfaced. Reflective facings function as vapor retarders.


Rigid insulation board is flammable and must be covered with a fire-resistant material, such as gypsum wall board, when it is installed on interior walls.

Some rigid insulation board is produced specifically for use on interior walls. This type is commonly made from wood or cane fibers with one side prefinished. Rigid insulation board designed for use as structural insulation is produced from compressed fibrous materials other than wood and does not have a prefinished surface. Rigid board panels made from polyurethane, polystyrene, polyisocyanurate, and phenolic are commonly used for exterior wall sheathing in new construction and to insulate basement and crawl space walls. Some R-values for common type of rigid insula­tion board are listed in Table 3-3.


Rigid board insulation has a high R-value and can be used in areas where space is limited, but it is also has a higher cost per inch than other insulating materials.


Rigid insulation board must be installed with tightly butted edges. Fill gaps of Vie inch or greater with pieces of insulation

Table 3-3 Some Rigid Insulation Board R-Values

R-Va/ue per

Inch of

Types of Rigid Insulation




Common Uses

Molded or expanded

R-3.6 to R-8

Exterior sheathing, interior

Polystyrene board

Basement walls, siding

(sometimes referred

Backer board, or

To as bead board)

Suspended ceiling panels

Extruded polystyrene

R-4.5 to R-5

Exterior foundation walls

Board (sometimes

Or surfaces, exterior

Referred to as blue

Wall sheathing, or interior

Or pink board)

Applications (above grade)

Unfaced polyurethane

R-5.6 to

Impregnated with asphalt for

And polyisocyanurate


Hot-mopped flat roof


Applications; vinyl-faced for beam ceilings

Faced urethane


Foil-faced exterior

And polyisocyanurate

Wall sheathing


Semi-rigid fiberglass

R-4 to R-5

Below-grade basement


Or crawl space exterior wall surfaces

Board cut to fit. Do not fill a gap between boards with other noninsulatng materials or any type of adhesive.

Posted in Audel HVAC Fundamentals Volume 1 Heating Systems, Furnaces, and Boilers