Answers to Insulation Questions #1 Answers to Insulation Questions #1
A. Insulate the belly (underside) of the home with R-19 batt or blanket insulation and make sure that it is protected from animals and moisture. A plastic ground cover under a mobile home will prevent moisture from diffusing into the floor. If the home is skirted, the moisture barrier should overlap at least 12 inches at all joints and extend at least six inches up the foundation piers. Skirting is not effective for saving energy, but it improves appearance and keeps out animals. It is import to vent all four sides for air circulation.
Q. Is there an insulation product that can be blown into a wall cavity without having to remove the cedar? Then do I have to worry about such things as vapor barrier?
A. You can have cellulose insulation blown in the walls. While the manufacturers of cellulose claim you do not need a vapor barrier with their product, the truth here is that most paint will qualify as a vapor barrier, especially after several layers have been applied to the wall.
Q. I've been given a bunch of R-19 batts and was wondering what would happen if I used them in walls that are a full 4 inches (which calls for R-15, I think). Are there some drawbacks to compressing these over-plump batts into these 4-inch spaces?
A. If you compress the larger batt into a smaller space, you will greatly reduce its insulation value. It is possible to carefully peel a thin layer of glass off the batt to the thickness you need. Make sure you wear gloves and a long sleeve shirt, and use a respirator.
Q. I have just purchased a fixer upper with no insulation, skirting or belly paper. Does the insulation and belly paper attach with a staple gun, like the wall of a house?
A. Yes you can put it up like in a home with a staple gun - just make sure you hit the floor framing. There is a spray adhesive that you can get at home improvement centers that will work for the belly paper. You just spray it on and press it to the insulation, pull it off wait a couple of seconds, then press it back on. You do have to make sure there is no dirt on the belly paper for it to work.
Q. Has anyone out there really looked at what the difference is in the batts for higher R-values?
A. R-Values are only a way of measuring the insulating value of a material under ideal conditions in a laboratory. They can be very misleading and do not always give a realistic value when applied to actual construction. It has been suggested that the Pink Panther be arrested for misleading people by not really showing the actual effective level of insulation. Several examples are:
1. The R-value of the pink stuff is for the material itself, not the value of a wall in real life. If you put R-19 pink stuff into a steel stud wall (16" on center) then the actual R-value of the wall drops to about R11 to R13. There is a table to show the actual values, but you won't find it in the pink information sheets. Wood studs are not as bad, but a traditional wood stud wall (2x4 16" on center) with R13 insulation will actually give you R11 to R12. The same applies to other similar insulation (cellulose, foam, etc.) because of the thermal short-circuiting of the studs.
2. The R-values are for bone-dry pink insulation. As little as 0.5 to 1 percent moisture can cut the insulation value by as much as 50 percent.
3. The test used (Guarded hot box) is an idealistic idea and there is no air movement and no pressure differential like there is in real life. This test shows off Fiberglas at its absolute best. There are other testing methods for walls that do take into account real-life factors such a mass, rate of heat loss and temperature cycles over a time period, but these are neglected in advertising.
4. The R-values of rigid insulation (extruded polystyrene, poly-isocyanurate, etc.) are far more realistic for actual construction since they are closed cell materials that are applied as continuous layer. These are not affected by the thermal short-circuiting of studs and similar materials. There may be some small amount of airflow through joints, but taping by perfectionists can minimize this.
The bottom line is: Just keep in mind what you are building with and how does it actually work in the structure. Advertising is just that, since the supplier will give his best values and let the user reduce the insulation value as he sees fit.
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