Research, prepare before adding attic insulation

March 30, 2011 

Recently, we had a new standing-seam metal roof installed on our home. The installation included removal of three layers of asphalt shingles from the one-quarter-inch-thick sheathing.

Immediately, we noticed that the house felt considerably colder. I suspect that is related mainly to the removal of the three layers of asphalt, which absorbed heat from the sun and served as additional insulation to the attic.

My questions pertain to adding more insulation to the attic, which is unfinished and not used for storage. Presently there are nine inches of fiberglass insulation, six inches between the floor joists and three inches placed on top, running perpendicular.

I would like to add more, but I’m not sure how much, or whether I should add on top of what exists or place it between the roof rafters. I’m aware that insulating the roof rafters would be more expensive as well as more time-consuming, and that I would need to pre-baffle the rafters to ensure adequate air flow.

From what I’ve seen, your reading of why the house feels colder is probably correct. In addition, the need to “pre-baffle the rafters” for adequate air flow indicates you have an excellent idea of what is required for a good job.

My experience has been with insulating the ceiling of a free-standing, unheated garage. The garage roof peaks, with one side having full southern exposure, the other northern.

I stapled Styrofoam baffles between the rafters from peak to eaves; hung the joists for the lower ceiling, then used R-30 fiberglass insulation – the R in R-value means resistance to heat flow. The higher the R value, the more effective the insulation.

You can, of course, add insulation to that already in your attic. When you do, use an unfaced – no paper or foil layer – batt. Otherwise, the insulation will trap moisture in the ceiling. Lay the batts perpendicular to the joists, so they do not compress the insulation below.

How much insulation is required depends on where you live and the expected temperature extremes, as well as the type of heat you use. You can find information from energy-related websites for your area, but in most northern climates, R-49 is recommended for attics.

Look into reflective systems, which are effective for reducing downward heat flow, for the roof rafters. These are made from aluminum foils with a variety of backings such as kraft paper, plastic film, polyethylene bubbles or cardboard.

When a single reflective surface is used alone and faces the attic, it is called a radiant barrier, and is sometimes used to reduce heat gain in summer and loss in winter.

While we know enough to insulate, we usually forget about air sealing. Fill all cracks between the living area and the attic with caulk or expanding foam.

For more information, check out the U.S. Department of Energy’s Energy Savers website at www.energysavers.gov.

We had a steel front door installed 15 years ago. The installer told us to wax it to maintain it. We did. Because of the amount of sun that hits the front of our house, the paint gave out. It has been repainted. Would you recommend waxing it, as we did previously?

Never mess with success. The sun may have done in the paint job more quickly had you not waxed it.

Questions? Email Alan J. Heavens at aheavens@phillynews.com or write him at The Inquirer, Box 8263, Philadelphia, Pa. 19101. Volume prohibits individual replies.

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