Q: What is the safest and most effective insulation for our attic crawl space? I am considering having new insulation installed—most likely in just the crawl space above our ranch house. What is the most environmentally safe and nontoxic insulation available? Would that insulation also be the most energy-efficient?
Sent by Allison
Editor: Here's what our friends at Green Home Guide have to say.
Answered by Ian MacLeod, MacLeod Design & Construction:
By crawl space above your house, I assume you mean the attic area. For this application, I would recommend either:
- cotton batt or
- blown-in cellulose
These are both nontoxic, no-VOC, and formaldehyde-free. Both products also have good soundproofing qualities, contain a high amount of recycled material, and are easy to work with. In fact, I installed both in my own house during a recent remodel.
Soy-based spray foam products
There are also fairly new soy-based foam products that can be sprayed on walls or in attics between ceiling joists.
- The main advantage of spray foams is that the foam will expand during installation to fill all cracks and voids to create a continuous air barrier that prevents warm air from leaking out of your house.
- The R-value depends on whether you choose an open-cell or closed-cell foam. (Closed-cell foam's R-value is higher.)
- The manufacturers claim there is no offgassing once the foam dries and that it is mold and mildew resistant.
The main drawback of foam products is that they tend to be very expensive compared to other options; for this reason, my company usually installs cotton or cellulose insulation.
We avoid fiberglass because of formaldehyde issues and general itchiness, and also because it is difficult to install correctly. (You have to avoid compressing it and be careful to leave no gaps or air-spaces.)
Cotton batts are available in R-13, R-19, R-21, or R-30 insulation values, in either 16- or 24-inch widths. Cotton batts are made of 85-percent post-industrial recycled natural fibers, mostly ground-up blue jeans.
- Batts are four feet long and can be simply laid between ceiling joists.
- You can do this yourself or you can hire a professional.
Minor disadvantages to cotton batts are that they are slightly harder to cut than fiberglass and the bundles are somewhat bulky because the cotton does not compress much. The cotton batts are slightly oversized compared to standard joist or stud bays so that when stuffed in place they have a good friction-fit and fill the cavities completely with no air gaps.
See Bonded Logic's website for more information.
Blown-in cellulose is an excellent option for an attic because it will fill all the joist spaces completely with very few air gaps. It is also very easy to install a higher thickness for greater R-value.
- Loose cellulose is made of 85-percent recycled material, mostly ground-up newspaper.
- It resists rot and mildew, and is treated with boric acid as a fire retardant.
See the websites of Bonded Logic and the Cellulose Insulation Manufacturers Association for more information. If you want to do the project yourself, Home Depot will loan a blower when you buy a minimum amount of cellulose insulation. However, if you want to install loose cellulose into walls, underfloor areas, or cathedral ceilings, I strongly recommend hiring a licensed professional.
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