Add Insulation to Your Attic or Floor
A little history on retro-insulation
In the 1960s and later there was a big push for electric heating and cooling. The local electric company had a package deal for select groups of people where the company paid to properly insulate homes if the homeowner would install electrical heating and cooling equipment. This was a great deal and meant that I had a lot of work. Many older homes had no insulation. This meant we crawled under floors and installed rock wool and fiberglass batts between floor joists. Hollow exterior walls had part of the exterior siding removed, a hole drilled in the wall at the top, and loose rock wool was blown into the hollow space between each stud. Brick, rock, and stucco walls presented particular problems but we managed to develop ways to do the job. Attics almost always had rock wool blown in to a depth of six inches.
How much insulation do you need?
Six inches (R-19) was the standard depth for insulation during those days. Studies of the time showed that anything over nine inches of insulation (R-30) was a waste of money. I don’t believe we could easily have bought nine inch thick batts back then. We could blow in nine inches of loose rock wool, but rarely did. Now, in the early Twenty Second Century, we find nine inch batts almost everywhere. If you have a newer home you probably don’t need to worry about insulation much. If your home is 10 years or older then you need to take a look in the attic.
If you have a concrete floor, the floor doesn’t matter much. If you have a crawlspace, you might take a look at the insulation under the floor. Four inch batts with a vapor barrier toward the living area is adequate. It’s no fun crawling around under a house so hopefully you don’t have a problem. If necessary install insulation between the floor joists with staples and plastic straps nailed to the bottom of floor joists. You can find all kinds of critters under a floor. I’ve been growled and hissed at, stung, bit, and sprayed by a skunk. So–have fun.
On to the attic. What kind of insulation does an old installer prefer? Fiberglass batts. For most of the Twenty First Century everybody understood that you need a vapor barrier to stop condensation when warm air encounters cold air. Batts came with and without vapor barriers so this worked well. Blown insulation is another matter. Except for a very few forward thinking individuals vapor barriers were left out of homes where insulation was blown in. Over a period of many years this caused problems in rooms that often had higher humidity–like bathrooms and garages with unvented dryers. The texture or paint on drywall ceilings would come loose and fall. In some cases the sheetrock ceiling would fall. If you’ve seen this happen now you know why. I mention this because it’s a problem when we add more insulation.
If your original insulation job was batts with a vapor barrier you’re in great shape for an upgrade. After 20 or 30 years that nice, fluffy six inches of blown in rock wool or fiberglass has compacted to two inches or less. In this case you have two choices. Take out all the loose insulation and install batts with a vapor barrier, or bite the bullet, don’t worry about the vapor barrier, and install batts with no vapor barrier over the old insulation crosswise to the ceiling joists. I go with the second choice. The first is just too much work for this old man. When I repair drywall ceilings I install batts with a vaper barrier as I go. Otherwise I forget it. I recommend installing six inch batts, but four, or nine are fine. Tight attics may require that you blow in loose insulation.
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