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Green Building Blog

Attic-Insulation Upgrade

Seal air leaks first; then add extra insulation for an energy-saving improvement with great bang for the buck

Blown-in loose-fill fiberglass or cellulose can cover existing insulation.

Do you want to keep your heating costs from going through the roof? It’s easy: Keep your heat from going through the roof. Saving money on heating-fuel costs is a lot simpler than negotiating with OPEC or your local utility. On a recent upgrade in the attic of a 1950s-era house (one of two projects shown here), I air-sealed and spread a 12-in.- deep layer of cellulose throughout 1500 sq. ft. of space in about a day. Coupled with other energy-saving improvements made to the home, the result was that the owner saw his heating and cooling costs reduced by half compared to the previous year, even in the face of higher electricity and heating-fuel costs.

I typically focus my efforts to improve the energy efficiency of an attic on two main areas: sealing air leaks in the ceiling and increasing the amount of insulation.

The payback period for tightening a leaky ceiling can be as short as a month. Adding insulation might take a few heating or cooling seasons to pay off, but the wait is relatively brief. I estimate the payback for air-sealing and upgrading attic insulation to be realized in three years.

On these projects, I also chose to install a radiant-reflective membrane. Besides reducing radiant-heat gain from the roof, the membrane makes the attic more attractive and dust-free for storage use, and it keeps the blown-in insulation from blocking the rafter bays. While they can reduce peak attic temperatures by 10°F to 30°F, the barriers haven’t proved to be cost effective in all geographic

regions, or in attics that are adequately insulated, that are air-sealed, and that have well-insulated, wrapped air-handling equipment and ductwork. you are probably better off spending the money on more insulation and air-sealing than on a…

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  1. Pat Murphy | | #1

    Costs of labor
    Great article. One might recall that Mike had an article in Fine Homebuilding which is worth reviewing.
    17 hours of labor seems like a good estimate. What is the estimated labor costs? At $50 per hour the labor is $800 compared to the material cost of $500. Is this about right? high? low? 1500 square foot size implies a cost of about $1.00 per foot. This seems a bit low.
    Also in air sealing is the older insulation removed? Is there a cost estimate for that?

  2. User avater GBA Editor
    Martin Holladay | | #2

    Response to Pat Murphy
    The only way to determine your costs is to solicit bids from contractors. While a labor rate of $50 per hour may be normal in your area, the labor rates in this part of Vermont are lower than that. That doesn't make $50 per hour unreasonable; labor rates vary from one region to another.

    It's impossible to guess how many hours it will take to air seal an attic without looking at the job. Every job is different.

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