Fiberglas Insulation

Fiberglas Insulation is the norm in residential construction. Because it is ubiquitous, it is also the cheapest insulation and can be installed easily, and poorly, by do-it-yourselfers and professionals. The problem with this insulation material is it is difficult to precisely fit in wall cavities that have romex, conduit,  electrical boxes, pipes and framing irregularities.  A second problem has to do with air movement through the insulation. If a wall isn't constructed properly, air can infiltrate the cavity and move freely through the insulation, reducing the R-Value of the insulation.

Fiberglas can be chopped up and blown through holes cut into a netting or polyolefin, stapled and glued to the face of studs. This is called a B-I-B (or blown-in-blanket) system. The advantage to this method is that the fiberglas flows around all irregularities in the cavity, including romex, electrical boxes, and wood framing. If installed too densely, the netting or sheet can bulge out causing the drywaller headaches as he tries to push the drywall tight to the face of the studs. If too fluffy, then air infiltration can still rob R-Value from the insulation.

Fiberglas is also commonly blown into attics as chopped fiberglas. It is important that the installer blow it in so that it is fairly dense, or air infiltrating through the material renders it less effective.

Cellulose Insulation

Cellulose insulation is commonly made from recycled newspapers and treated chemically to make it fire resistant. It can be blown into walls from the outside through holes cut in the sheathing (in existing homes) or from the inside through holes cut in drywall and plaster. It can also be used in a B-I-B system or blown in wet into exposed stud cavities, where it dries over a number of days. Cellulose has about the same R-Value as fiberglas batts. It also has the advantage that it can be installed much more densely, which reduces the impact of air infiltration.

Cellulose can also be used as an attic insulation. When blown into an attic, it tends to settle slightly, compressing in the process and is more resistant to air infiltration.

Foam Insulation

Foam Insulations are products that are sprayed into wall and  roof cavities. They have numerous advantages. They eliminate air infiltration into cavities, they eliminate convective loops within the insulation and they flow around all obstructions within the cavity, completely insulating the spaces they are sprayed into. There are two basic kinds of foam insulations, open-cell and closed-cell. 

Open-cell insulations have an R-Value similar to fiberglas, about 3.5 per inch and are vapor-permeable. The open-cell product we use is called Icynene.

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                                          Icynene in walls and box sills


                                      Icynene in knee walls and rafters

Closed-cell insulations have an aged R-Value of 6.2 per inch, are vapor impermeable and are much denser and stronger than open cell insulation. The product we use is from Johns Manville and called Corbond. Three inches of Corbond has about the same R-Value as five-and-a-half inches of Icynene, and unless specified otherwise, that is the thickness normally sprayed into a 2x6 stud cavity.

Both kinds of foams are great insulations to use in our structures. They not only save energy, in some cases dramatically so, but also create much more comfortable living spaces. 

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