Benefits of using Rigid Foam Board Insulation
- Density - Density provides hi R-value with minimum thickness making rigid insulation more resistant to air and water vapor movement than fiberglass batts or cellulose.
- High compressive strength - rigid insulation provides a solid structure under the roof deck that can withstand the weight of both equipment and light foot traffic.
- Low weight makes rigid insulation boards easy to install and less expensive to ship.
- Resists outside air infiltration when joints are sealed with tape or caulk.
- New products are made without ozone depleting chemicals for virtually no global warming impact.
- Can be installed with full coverage over studs instead of just between them to eliminate the heat loss path through framing members.
- Non-hazardous to install - no fibers or fumes to inhale, non-irritating to skin.
- No deterioration of R-value over time - rigid insulation does not lose R-Value over its service life.
- Green - A manufacturing study showed that the energy required producing polystyrene foam insulation is 24 percent less than the energy required to make the equivalent R-value of fiberglass insulation.
- Rigid insulation "breathes" instead of trapping moisture like fiberglass or cellulose and therefore does not require the venting methods used for other insulation materials to prevent trapped moisture within walls, ceilings and roofs.
- Highly resistant to mold
- Not a food for insects
- Good acoustical insulation properties
- Can be used in structural insulated panels or for insulating concrete forms.
Expanded polystyrene (EPS) or beadboard, has been used as common household insulation since the 1950s. EPS is environmentally friendly as it is not manufactured using CFCs or HCFCs- both ozone-depleting chemicals. In addition to insulation, EPS is commonly used to make coffee cups and packing peanuts for shipping.
EPS is closed-cell foam made from polystyrene (a type of plastic) beads mixed with pentane and steam, used as a blowing agent, to expand the beads under pressure into foam, which forms thousands of tiny air pockets in the finished board. As air is a poor conductor of heat, these tiny air pockets will block the transfer of heat through the foam and trap expanding warm air.
EPS is molded into large sheets with R-values ranging from 3.8 to 4.4 per inch, depending on the density of the material. However, air spaces in EPS can accumulate and retain water. Because water is a good conductor of heat, some form of moisture barrier may be required to prevent this problem in high humidity areas, especially when EPS is used around foundations. To make the insulation more waterproof, EPS boards are available with optional thin foil or plastic facings.
Extruded polystyrene (XPS) or blueboard, is also a closed-cell foam insulation made from polystyrene plastic beads mixed with chemicals to turn them into a liquid before using a blowing agent to turn it into foam. The foam is forced through a shaping die, cooled and cut into panels.
XPS is more consistent in density and has a higher compressive strength than EPS making it better suited for use in roof assemblies and structural insulation panels. Higher density makes it more resistant to moisture than EPS, and XPS has a slightly higher R-value of R-5 per inch. Because of its superior properties, XPS is more expensive than EPS.
Polyisocyanurate or Polyiso, has the highest R-value per inch of thickness of the different rigid foam insulation types with an average R-value between 5.6 and 8 depending on the facing material. Facings such as plastic or aluminum foil increase its resistance to both moisture and radiant heat transfer. Polyiso is commonly used in roofs and cavity walls because of its thinness.
Polyiso is touted for being an economical choice. Its higher R-values per inch allow for savings on other building materials like thinner walls and roofs and their associated shorter fasteners.
According to the Polyisocyanurate Insulation Manufacturers Association, polyiso is a completely green building product as it no longer is made with either of the ozone depleting chemicals - CFC and HCFC. In addition, construction site waste can be recycled. Other beneficial characteristics of polyiso include its resistance to solvents in common construction adhesives and high fire test ratings.
Foil faced polyiso insulation has the highest R-value per inch of any type of mass insulation currently produced. When installed facing an air space of at least 1", the R-value will increase by 2.89. ASHRAE assigns a 1" air space R- 2.77. The Masonry Advisory Council adds an additional R-2.89 to polyiso insulation for a foil facing.
Rigid and Reflective Insulation in a Foundation Wall
(listed from outside to inside)
- Concrete Wall
- Rigid Insulation
- Reflective Insulation
- Wood Strapping or Studs (airspace)
- Drywall
|
 |
Rigid foam insulation boards used to insulate the interior of masonry walls do not require an additional vapor barrier. Wood strapping is attached to the wall and the insulation is installed over the strapping. If a foil-faced board or reflective insulation is used also, the foil side should face the room and an additional layer of wood strapping is needed under the drywall to create an air space. Fire safety codes require that at least ½-inch thick gypsum board (dry-wall) be placed over rigid foam insulation. The drywall is then attached to the wood strapping or underlying masonry with nails or screws. For insulating an unventilated crawlspace, rigid insulation boards can be glued directly to the wall.
| 
