Bag tricks to seal and insulate

Posted Wednesday, October 26, 2011 in Sustainable Maine

by Paul Kando

Bag tricks are a quick and easy way to seal and insulate wall and ceiling cavities. Adapted to varied situations they are excellent low cost do it yourself improvements. All you need is pieces of left over insulation (fiberglass batting is fine), a plastic bag and physical access to the cavity you intend to air seal and insulate.

Let pictures speak. Figure 1. shows the top of a partition wall being blocked form the attic.

On Figure 2. the upstairs floor is isolated from the unheated space behind the knee-wall. While there, you also have the chance to insulate the knee wall itself. Check also if the roof section that forms the slated ceiling in the top floor room is insulated. If  not, this is a good time to blow it full of insulation. You may even want to blow the whole space behind the knee wall full of densely packed cellulose, seeing to it that the roof remains ventilated.

Figure 3. suggests a way to block the large uninsulated space between a lower floor ceiling and the floor above. A standard 3" blow-hole is drilled in the approximate center of each bay formed by adjacent joists. An empty plastic contractor bag is inserted through the hole in such a way that its opening remains outside. The hose of the insulation blower is then inserted into the bag through the blow hole and the bag is blown full of densely packed insulation. The bag will jam against the walls of the cavity, blocking and insulating it. (Care must be taken that there be no recessed light cans near enough for the bag to come closer than 4-5" to them.) Finally the blow hole is plugged.

These bag tricks work best if the outer walls are also blown full of densely packed cellulose insulation, which tends also to retard air movement. There are also new foam products available which can be used in place of the blown cellulose. They provide a higher R value, but may also cost more.


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