Rigid roof insulation is an important component in low slope roof applications and serves several vital purposes. Roof insulation provides a relatively smooth substrate to which other roofing materials can be applied; reduces the energy required to heat and cool a building; and can provide important fire-resistance characteristics. The main types of rigid roof insulation in use today are polyisocyanurate, perlite, and fiberboard.
Polyisocyanurate foams are manufactured in board form, typically in 4' X 4' and 4' X 8' sizes and can be made in thicknesses from 1/2" to 4" thick. Tapered boards are also made, with the most common slopes being 1/8" and 1/4" per foot. The foam is manufactured through a chemical reaction of two liquids, polyisocyanate and polyol. The reaction causes the liquid to rise and harden into a cellular foam.
Perlite insulation is classified as an inorganic, rigid board insulation. It is available in 2' X 4' and 4' X 4' boards with common thicknesses of 1/2" to 3". Perlite has excellent fire resistance and can be used with other less fire resistant insulations to qualify a roof system for an acceptable fire rating. Perlite insulation is composed of expanded volcanic glass and wood fibers bonded with asphaltic binders, which allows for a board that is lightweight and high in compressive strength.
Fiberboard is a rigid, organic insulation board composed of wood, cane, or vegetable fibers mixed with various types of fillers and binders. The insulation may be either asphalt impregnated or asphalt coated to enhance its moisture resistance. Fiberboard is available in 2' X 4', 4' X 4', and 4' X 8' boards with thicknesses ranging from 1/2" to 2". It also is available in a normal and high grade density.