Attic Insulation?

Question

Out of curiosity, with a poorly insulated attic, aside from the warm air below raising and escaping through the attic, does the cold air above act like a vaccum, succing the warm air out even quicker?

Now to my attic, we renovated the rear portion of our 1968 house in Boston and during the process I reinsulated the back portion with faced R-38 and am now in the process of running R-13 or R-19 perpedicular.

The front portion of the house/attic insulation is untouched. It is a double faced R-13 at best.

My questions are:

Can I keep the double face bats down and run unfaced R-19 over it, then R38 perpandicular OR should I remove the existing bats, place new faced R-38 with R-13 or R-19 perpedicular, thus not wasting anything allready up there?

Thanks -

Sean

Thanks handerande. After further reading and calling my local Home Imprvement store, I am going to blow in the insulation, easier and more cost affective. I wish I would have done that to the rear half of the house.......

Thanks all.

ranger_co_1_75...now I am confused. I thought I read that the blown in Cocoon insulation does not settle....can anyone confirm from experiance?

Answer 1

Basically insulation slows air transmission between the two spaces whether hot to cold or cold to hot.
I would definitely leave the existing insulation in place and cover with as much faced (paper down) or unfaced perpendicular.
This is such a hateful job I would put one layer of the highest R-value stuff I get up there.

Answer 2

I have been down this road many, many times. Experience shows that Batts are the best way to go.

Blown insulation is the cheapest way to go, but it settles and compacts to less than 1/4 it's thickness after a couple of years. So if you blow in 12 inches of insulation, in a few years it will be less than 3 inches of insulation and you will no longer have the R value you originally wanted, so you will need to insulate again.

In addition, not only is blown insulation a poor quality insulation, it is extremely messy to install. It is like being inside a dust storm that is hazardous to your eyes and respiratory system.

Batts stay at their installed thickness for many, many years. Lay the Batts over the existing insulation. You do get a small amount of airborne insulation from moving the Batts around, but nothing like blown insulation.

Whichever type of insulation you use, you will need a respirator and goggles, and probably want to throw your clothes away when you are done.

Answer 3

when vapor leaves your house it will freeze in the winter. If the vapor leaves through your insulation the water will freeze and accumulate in the insulation and reduce its r value. For this reason, it is best to put an additional vapor barrier such as plastic sheeting down under attic insulation, and have the backing face down. thus the vapor is forced to leave through other means than through your insulation. additionally make sure you have proper venting of bathrooms to minimize the amount of vapor trying to exit through your ceilings. If you may want to use the space for living in the future, I would use solid insulation that is not effected by moisture and put it just under the roof, otherwise just above the ceiling is preferred. if you live in a place where it never freezes this may not be as much of a concern If you are having blown in insulation installed (which is not what was in the question) then no vapor barrier will be used

Answer 4

Heat rises and cold sinks. So if the ceiling is not insulated properly, the heat will be consumed by the cold above it. By all means leave the existing insulation in place. While bats of insulation are an acceptable addition, a blown in fiberglass product will cover and insulate better. It's much easier to install, and you can usually get a free blower rental if you buy the insulation at one of the big home improvement stores.

Answer 5

I have blown cellulose insulation (what they sell at Home Depot) into two houses. I didn't notice nearly the degree of settling that another poster here cites -- but I wasn't trying to find it, either.

It is indeed *very* dusty. Use a decent dust mask and goggles -- although as I recall I ended up pulling them off sometimes because they fogged up so much. No amount of money would induce me to work with blown fiberglass.

I had my son in the driveway feeding the machine. He thought of using cell phones to communicate; then we switched to the two portable land-line phones we had. Unfortunately neither of us was smart enough to keep an eye on the time, and the police showed up to shut us down at 2 a.m. What a great way to make myself known to my new neighbors.

By the way, it isn't really correct to say that *heat* rises; clearly warm sunlight comes down to us. What does rise is hot *gas* (i.e. air). Such convective currents can carry a lot of energy (and moisture) up into your attic, so indeed seal any leaks you find (e.g. around pipes and wires, open tops of soffit walls, etc. But don't expect blown or batt insulation to do that. You need to use caulk or that sticky spray foam stuff.

Blow insulation will reduce conduction of energy through your ceiling material -- as would insulation installed in a wall or floor.

Answer 6

Good Idea! Blown in insulation is by far the easiest and best way to re-insulate any structure.

Answer 7

I would.