July 20, 2008
Adding Insulation
IF YOUR HOUSE hasn't been able to keep out the winter cold, perhaps you should consider an insulation makeover.
A couple hundred dollars of fiberglass insulation and a few weekends might be all that's needed to blanket your attic with a layer that will keep air - and fuel bills - from rising through the roof. In the summer, this same layer keeps hot attic air from penetrating the living space.
Fiberglass insulation is light, easy to cut and fits into place. So adding a layer to your attic can be a cost-effective solution.
First, two suggestions: Be sure you have ample access and work space in your attic. You'll need enough room to work between joists or lay sheets of plywood for temporary flooring. You don't want to fall through an open floor.
Also, installers should wear gloves, long-sleeved shirts, dust masks and eye protection. Airborne glass particles can irritate eyes, noses and throats.
OK, let's get to the attic. If you have insulation between the exposed studs of existing attic walls, you're probably better off leaving the situation as is. (Why stir up all that mess?) We'll stay away from loose-fill insulation that is applied with blowing machines, simply because it almost always has to be done by a professional. If you are trying to insulate enclosed walls, this is obviously the best option. But in both cases, it's better left to a pro.
Your first step is to inspect the area you want to insulate. In this case, let's assume you're adding insulation to an attic floor that is unlikely to be converted to living space. (In an attic that could be converted, the floor insulation that's in place is likely sufficient.) An attic that won't be converted usually can take another layer of insulation, which can be laid right over exposed joists.
Measure the length and width of your floor to determine square footage (width by length equals square feet, so 10 feet by 10 feet equals 100 square feet).
Fiberglass insulation is commonly available in rolls 3 1/2 or 6 inches thick and 16 or 24 inches wide. Its two forms are batt (precut to lengths of 4 feet and 8 feet) and blanket. Blanket insulation generally is 3 1/2 inches thick and 56 inches long or 6 inches thick and 32 inches long.
Because insulation also has vapor- barrier properties, you should understand the difference between "faced" and "unfaced" insulation. Faced insulation simply means one side is backed with a paper or foil that retards moisture penetration. Unfaced insulation is used in most upgrade projects because it often covers an existing layer of insulation that has a vapor barrier.
For upgrading an attic floor, use unfaced insulation in blanket form. Your existing insulation should fit between the joists (probably 16 inches apart) with the paper side facing down. The paper acts as a vapor barrier. Be sure to add only unfaced insulation; you don't want a second layer of vapor barrier. To best cover cracks and openings, the new layer should be laid perpendicular over the existing insulation.
Before you add, you'll also need to determine the R-value of your exist- ing insulation. What's R-value? The ability of insulation to slow the transfer of heat is measured in R-values. ("R" means resistance to heat flow.) The higher the R-value, the better the insulation.
States and counties across the country have determined recommended R- values for residential insulation. The three most common applications are attic floor, exterior wall and a floor over an unheated basement or crawl space. For the Northeast, which includes Long Island and New York City, these are the recommended R-values:
Attic floor R-49
Exterior wall R-19
Floor over unheated area R-25
Use this formula to determine existing R-value: Thickness of fiberglass (in inches) times R-value per inch. For fiberglass, use 3.2 as the R-value per inch. (So a 6-inch-thick layer in your attic has an R-value of 19.2.)
Under the guidelines above, this would mean you could add another 9 1/2-inch blanket of unfaced fiberglass to your attic.
R-value, faced, unfaced - it can get confusing. So first determine your needs. Then check prices, which can vary. For example, a quick check last week found R-11 rolls of unfaced insulation (3 1/2 inches thick) that cover 75 square feet running about $15. Unfaced R-19 rolls (6 inches thick) covering 88 square feet were about $27. Faced rolls are slightly higher.
Here are a few other installation tips:
Use a 2-by-4 and a scrap piece of plywood to make the trimming of thick fiberglass easier. Lay the insulation on the plywood with its paper or foil side facing up. After measuring the desired length, place the 2-by-4 across the fiberglass. Compact the batt by kneeling on one side of the 2-by-4 and pressing down with your hand on the other. Draw the utility knife across the compacted area for a smooth, clean cut.
Even though fiberglass insulation is fire resistant, never cover electrical boxes, fan or light fixtures or soffet vents. Covering "hot spots" could lead to a fire hazard, and covering soffet vents will retard necessary circulation of attic air. Trim the insulation so electrical boxes are exposed.
Consider a painter's suit as part of your protective clothing. This one-piece coverall can be purchased for about $10 and will keep fibers out, especially if you tape down the wrists and ankles.
Try the newer brands of "itchless" fiberglass batts, such as Miraflex from Owens Corning. This newer insulation is wrapped in polyolefin, which allows for moisture and air circulation but keeps fibers from spreading through the air.
WANT MORE information on fiberglass insulation? Here are some sources: North American Insulation Manufacturers Association 44 Canal Center Plaza Suite 310 Alexandria, Va. 22314 Phone: 703-684-0084 E-mail: insulation@naima.org www.naima.org Insulation Contractors Association of America 1321 Duke St. Suite 303 Alexandria, Va. 22314 Phone: 703-739-0356 www.insulate.org
You also can visit the Web sites of these leading manufacturers of fiberglass insulation: CertainTeed Corp.: www.certainteed.com Georgia-Pacific: www.gp.com Owens Corning: www.owens corning.com
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