Insulation - Does Your Home Need More Insulation? - 5/1/2004 - House Energy Efficiency Insulation

Insulation - Does Your Home Need More Insulation?

To begin to answer this question, you must first find out how much insulation you already have and then determine how much more would be cost-effective. Many older homes have less insulation than homes built today. A qualified home energy auditor will include an insulation check as a routine part of an energy audit. For information about home energy audits, call your local utility company. State energy offices are another valuable resource for information. An energy audit of your house will identify the amount of insulation you have and need, and will likely recommend other improvements as well. 

If you don't have someone else inspect your home, you'll need to look for insulation in several places. Figure 48 shows the places in a typical house where insulation should be installed. These are the areas you should check. In each location, you'll need to measure the thickness of the insulation and identify which type of insulation was used. See Figure 49. 

Your home may have one or more of several different insulation materials. Mineral fiber insulation, including fiberglass and rockwool, is produced from either molten glass, slag, or rock. Fiberglass insulation is usually very light-weight, and yellow, pink, or white in color. Fiberglass can be found in loose-fill and blanket, either batt or roll, forms. Rockwool loose-fill is usually more dense than fiberglass, and is most commonly gray with black specks. Some rockwool products, however, are near-white. Loose-fill cellulose insulation is commonly manufactured from recycled newsprint, cardboard, or other forms of waste paper. Most cellulose is in the form of small flat pieces rather than fibers. However, some cellulose products are so finely divided they look fibrous as well. Vermiculite- and perlite-loose-fill products are no longer commonly used as home insulation, but you may find them in an older home. They are produced by expanding naturally occurring minerals in a furnace. The resulting granules are non-combustible and are commonly poured-in-place. 

First, check the attic; then check walls and floors adjacent to an unheated space like a garage or basement. In these places, the structural frame elements (the ceiling joists or wall framing boards) are often exposed, making it easy to examine the insulation (if any) and to measure the depth or thickness of the insulation. It is more difficult to inspect finished exterior walls. One method is to use an electrical outlet on the wall, but first be sure to turn off the power to the outlet. Then remove the cover plate and shine a flashlight into the crack around the outlet box. You should be able to see whether or not insulation is in the wall. You may need to pull a small amount out to determine which type of material was used. Also, you should check separate outlets on the first and second floor, and in old and new parts of the house, because wall insulation in one wall doesn't necessarily mean that it's everywhere in the house. An alternative to checking through electrical outlets is to remove and then replace a small section of the exterior siding. 

Next, inspect and measure the thickness of any insulation in unfinished basement ceilings and walls, or above crawl spaces. If the crawl space is not ventilated, it may have insulation on the perimeter wall. If your house is relatively new, it may have been built with insulation outside the basement or foundation wall. However, this insulation would not be visible because it would be covered by a protective layer of stucco, plastic, fiberglass, metal flashing, or a rigid protection board. The builder or the original homeowner may be able to tell you if such exterior insulation was used. 

Don't overlook another area in your home where energy can be saved--the ductwork of the heating and air-conditioning system. If water lines and the ducts of your heating or air-conditioning system run through unheated or uncooled spaces in your home, such as attic or crawl spaces, then the water lines and the ducts should be insulated. First check the ductwork for air leaks. Repair leaking joints first with mechanical fasteners, then seal any remaining leaks with water-soluble mastic and embedded fiberglass mesh. Never use gray cloth duct tape because it degrades, cracks, and loses its bond with age. If a joint has to be accessible for future maintenance, use pressure- or heat-sensitive aluminum foil tape. Then wrap the ducts with duct wrap insulation of R-6 with a vapor retarder facing on the outer side. (If you live in the deep South or southern California, you can use R-4 insulation.) All joints where sections of insulation meet should have overlapped facings and be tightly sealed with fiberglass tape; but avoid compressing the insulation, thus reducing its thickness and R-value. In many parts of the country, this type of insulation will pay for itself in energy saved. 

Return air ducts are more likely to be located inside the heated portion of the house where they don't need to be insulated, but they should still be sealed off from air passageways that connect to unheated areas. Drywall-to-ductwork connections should be inspected because they are often poor (or nonexistent) and lead to unwanted air flows through wall cavities. 

The amount of money you are willing to invest in insulation will of course depend on your personal finances. But remember that the initial investment will pay for itself in reduced energy consumption, particularly where the amount already installed is substantially less than recommended. If fuel and electrical power costs rise, it will make even more sense to invest in insulation. If you are financing a new home, or a major home improvement, you may wish to check to see if banks in your area allow larger loan amounts for energy efficient housing. 

The insulation levels recommended here were chosen based on a life-cycle cost analysis. This analysis includes many assumptions about your house, heating and cooling system efficiencies, and what rate of return you would like to earn on your investment. 

Determining The R-Value You Need For A House

The amount of insulation you need depends on the climate, type of heating (gas, oil, electricity) you use, and the section of the house that you plan to insulate. The attic is the first area to consider because it is accessible and therefore less expensive to insulate. 

Figure 47 and Figure 17 will help you to identify the type of insulation and its R-value as presently installed. Determine the kind of insulation you have from Figure 49, and circle it in Figure 47. Then, multiply the thickness of your insulation by the "R-value per inch". This will give you the total R-value of your existing insulation. 

The next step is to compare the R-value of your insulation with the recommended R-values for your house and your type of space heating. Using these recommended R-values, subtract the R-value of the insulation already in your home. The result will be the R-value you should add. 

You can use the information in Figure 47 to estimate the thickness required from different materials to achieve this added R-value. This approximate thickness may help you choose your insulation material, especially if you are working within a confined space. However, when purchasing or installing new insulation, always consult the product label for accurate thickness information. Many special products have been developed to give higher R-values in a smaller thickness. On the other hand, some materials require a greater initial thickness to offset eventual settling or to assure that you get the rated R-value under a range of temperature conditions. 

When you stack new insulation on top of existing attic insulation, the existing insulation is compressed a small amount. This will slightly decrease the total R-value of the insulation. This effect is most important if the new insulation is more dense than the old insulation. You can compensate for this stacking effect and achieve the desired total R-value by adding about one extra inch of insulation if the old insulation is fiberglass, or about 1/2 inch if the old insulation is rockwool or cellulose. 

For example, consider an existing house in St. Paul, Minnesota (zip code 55103) with a gas furnace. The recommended R-value for attic floor insulation for this house is R-38. If the existing attic floor insulation has an R-11 insulation value, then an additional R-27 would be needed to bring the attic floor insulation up to the level recommended for that house. The homeowner could then check Figure 49 to find several choices. Remember to buy the new insulation based on this R-value, and to check the product label to determine the proper thickness of the new insulation. Choosing a slightly higher level of insulation, such as R-30, would serve to offset the stacking effect discussed above. 

Use this formula to determine the R-value of your existing insulation:
	x		=
Thickness (inches)	x	R-value per inch	=	Total R-value

Use this formula to determine how much insulation you need to add:
	x		=
Recommended R-value	x	Existing insulation R-value	=	R-value needed

Do you want to know if you have the space available to add the insulation you need? Then use this formula to determine the approximate thickness you need to add:
	x		=
R-value needed	x	R-value per inch	=	Approximate thickness needed

However, remember to use the product information on the insulation packaging
to determine the actual thickness for any new insulation.