A couple of weeks ago we talked about insulating our attics with fiber glass insulation. This week we are going to look at using spray foam insulation. There are two types of spray, open cell and closed cell. Here’s the chart.
|Type||Cost||R Value||Water Barrier||Blowing Agent|
|Open Cell||$||3.7 / inch||no||water|
|Closed Cell||$$$||6 / inch||yes||chemical|
|Fiber Glass||$||3.3 / inch||no||none|
Foam insulation combines two chemicals and is applied by spraying them over surfaces or between roof rafters with a hose and nozzle unit attached to the insulation containers. The foam expands about eight times its initial volume and fills around wires, between cracks and in holes that fiberglass insulation could misses.
There are a number of good reasons for using foam over fiberglass.
1) If we have a finished attic, we can apply the foam behind our walls without having to tear out the walls and can still use the attic after the insulation is complete.
2) The foam will fill in voids and holes that otherwise would let in cold air.
3) The foam itself provides a vapor barrier unlike fiberglass that has to have a vapor resistant backing.
4) If we have exposed duct work in the attic and insulate the roof rafters, the duct work will not need its own insulation wrap.
5) The R value of closed cell foam insulation per inch is nearly twice that of fiberglass.
There are two big disadvantages of spray foam insulation compared to fiberglass.
1) For a 1,000 square foot attic space closed cell foam insulation will cost around $8,500 compared to $1,200 for fiberglass; 7 times as much.
2) The foam insulation takes more skill to apply than fiberglass, and requires very serious use of breathing masks. There are do-it-yourself kits such as Tiger Foam, but I wouldn’t want to do it myself. I would recommend getting a few of estimates from competent installers and have them take care of the masks and mess.
Spray foam can be applied to walls as well, but the payback in heating and cooling savings will be decades. The advantage in insulating our walls is comfort. The radiated heat or cold we feel from the walls will go away when our walls are insulated properly.
There are still tax credits up to $500 per year for all combined energy improvements. The credits run out at the end of the year. If you can take advantage be sure to file IRS Form 5695 with your tax return.