Rigid Insulation
Rigid insulations increasingly are coming into use in the North. Though a more expensive form of insulation than fiberglass batts or blown fiberglass or cellulose, the rigid insulations have certain advantages that sometimes make them worth the higher cost.
One popular type is urethane that can be purchased in rigid sheets or foamed in place on the job. Also called polyurethane or isocyanate polymer, urethane has the highest R-value (resistance to heat flow) of any material readily available. It is comparatively waterproof and holds up well if protected from sunlight by special surfacings applied within a few days of the time the urethane is laid down.
Urethane owes its thermal insulating and water resistance characteristics to the molecular structure of the material, mainly the large number of tiny closed voids within the urethane material. Urethane is formed spontaneously when certain relatively simple organic molecules are mixed (isocyanate plus polyether). These molecules rearrange themselves and join together into large interlinked chemically-bound arrays called polymers. It is as much art as science to get just the right mix that yields the desired end product since several components are required. Necessary ingredients are isocyanate, a polyether, a catalyst that helps the molecules to rearrange and join, a blowing agent to create closed cells in the structure and also another agent to control the cell size.
The ingredients are partially premixed into two containers for transport. When the contents are finally mixed together under pressure, the rigid urethane foam spontaneously forms. Different characteristics are possible by altering the mix used.
Easily confused with urethane because of the similarity of names is urea-formaldehyde rigid insulation. The confusion is unfortunate because urea-formaldehyde is dangerous and is now outlawed in most states. Urea-formaldehyde evidently is no longer available in Alaska, so one need worry little about it. Urea-formaldehyde and water are produced when urea (CON 2 H 4 ) and formaldehyde (CH 2 O) are mixed. The bonding is not strong enough to prevent formaldehyde from being given off, even at room temperature. Formaldehyde does nasty things to people; it gives them nausea, nosebleeds and headaches and makes them vomit.
Two rigid insulation materials now popular in the North are made from the molecule styrene (C 8 H 7 ). One is the blue-colored insulation sold by the Dow Chemical Company under the brand name Styrofoam. Chemically, Styrofoam is identical to the white colored polystyrene beadboard now readily available. These two insulation materials are made by merely heating collections of styrene molecules. The molecules link together, that is they polymerize, to form a rigid material with many closed air spaces contained.
Though more expensive than urethane, Styrofoam is not quite as good an insulator. However, it has much greater strength. Also, it is somewhat more impervious to water so is particularly suited for use underground and where bearing strength is critical, as under a concrete floor.
Polystyrene beadboard resists water reasonably well, about as well as urethane, but its thermal resistance is poorer than Styrofoam or urethane. Its thermal insulating quality is not much better than ordinary fiberglass, and it is about three times as expensive. However, it can be used underground, as can urethane, if conditions are not too wet and if high-bearing strength is not needed.
