Attic and Exterior Wall insulation?
Question:Location: Austin, TX
I'm purchasing a new house. The builder is putting fiberglass batt insulation in exterior walls and blow-in firberglass insulation (R-38, 12inches) in attic.
Attic:
1. Is R-38, 12" enough for firberglass fill? or should I go with cellulose. Cellulose seems to have issues with moisture and settling down overtime.
2. If I put cellulose, I think I cannot use that space at all, right? Is it okay to put a board to increase usable space?
Exterior Walls:
3. Anyone used cellulose for it? Is it worth the cost and maintenance?
4.. Is it worth the risk do it in both?
5. How to check if there any leaks or moisture buildup if I use cellular?
6. What are the maintenance costs?
Thanks in advance for your advice!
Answers:
I am sure the contractor is using fiberglass in the attic because he has access to the joists and can easily roll out the insulation. You can put down plywood or particle board on top of the fiberglass to make usable attic space with no problem. Cellulose is being used in the walls because unless you want to tear out walls and put in the rolled insulation, it is the easiest method to spray it in. The cellulose will settle after time, but we are talking about quite a few years. And any insulation is better than none. When we first moved into this house, there was NO insulation and we could sit inside the house and the wind outside would blow our hair. I have never had to Maintain insulation, it is just there. Unless it gets wet somehow and needs to be replaced, I can't think of anything you would need to do to it.
1. R-38 should be fine for insulation needs. You've mentioned cellulose settling. So will blown fiberglass. This is just loose fill. My recommendation for an attic would be batts the height of the joists. Then, blow fiberglass in to reach the height you're after (12 ").
2. What ever insulation you install, you'd have to tamp it down to the level of the joists if you're going to place boards on top.
3. In my experience, if you're really trying to increase the R-Value in the walls, you'll need to use 2x6 studs. The extra two inches of insulation will really increase your R-Value. It can cut heating/cooling costs in half. (Read this as the thicker walls will still pay for themselves, but it'll take a few years).
4. I wouldn't mix the two types of insulation.
5. Moisture build-up can be handled in the walls with a house wrap (typar, et al). Attics, you'll need a good roof with vents.
6. Long term maintenance is really nothing, unless you have a leaky roof or pipes. Water damage is the big pain.
12" of blown fiberglass is R-30. Cellulose is the best choice for walls and attic. walls done with cel. are about 30% more in cost, but you make your money back in 4 to 5 years in heating and cooling. plus outside noises are cut in half. cel. is also a better choice for the attic . cel. has alot higher of a fire rate.
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