Insulation: The Facts

Confused about R-values, rolled or blown-in insulation, vapor barriers and other insulation terms? This series of stories, adapted from the U.S. Department of Energy "Insulation Fact Sheet" explains the ins and outs of home insulation -- and may help you save significantly on your heating and cooling costs.

Topics covered in Part 2: Where should insulation be installed? * Basic Types of 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 1, below, 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

In unfinished attic spaces, insulate between and over the floor joists to seal off living spaces below.* 1A attic access door In finished attic rooms with or without dormer, insulate ... 2A between the studs of "knee" walls; 2B between the studs and rafters of exterior walls and roof; 2C ceilings with cold spaces above; 2D extend insulation into joist space to reduce air flows. All exterior walls, including ... 3A walls between living spaces and unheated garages, shed roofs, or storage areas; 3B foundation walls above ground level; 3C foundation walls in heated basements, full wall either interior or exterior. Floors above cold spaces, such as vented craw spaces and unheated garages. Also insulate ... 4A any portion of the floor in a room that is cantilevered beyond the exterior wall below; 4B slab floors built directly on the ground;** 4C as an alternative to floor insulation, foundation walls of un-vented crawl spaces; 4D extend insulation into joist space to reduce air flows. Band joists. Replacement or storm windows and caulk and seal around all windows and doors. *Well-insulated attics, crawl spaces, storage areas, and other enclosed cavities should be ventilated to prevent excess moisture build-up. **For new construction, slab on grade insulation should be installed to the extent required by building codes, or greater.

Types of Insulation

FORM	INSTALLATION METHOD	WHERE APPLICABLE	ADVANTAGES
Blankets: batts or rolls Fiber glass Rock wool	Fitted between studs, joists and beams	All unfinished walls, floors and ceilings	Do-it-yourself Suited for standard stud and joist spacing, which is relatively free from obstructions
Loose-Fill (blown-in) or spray-applied Rock wool Fiber glass Cellulose Polyurethane foam	Blown into place or spray applied by special equipment	Enclosed existing wall cavities or open new wall cavities Unfinished attic floors and hard to reach places	Commonly used insulation for retrofits (adding insulation to existing finished areas) Good for irregularly shaped areas and around obstructions
Rigid Insulation Extruded polystyrene foam (XPS) Expanded polystyrene foam (EPS or beadboard) Polyurethane foam Polyisocyanurate foam	Interior applications: Must be covered with 1/2-inch gypsum board or other building-code approved material for fire safety Exterior applications: Must be covered with weather-proof facing	Basement walls Exterior walls under finishing (Some foam boards include a foil facing which will act as a vapor retarder. Please read the discussion about where to place, or not to place, a vapor retarder) Unvented low slope roofs	High insulating value for relatively little thickness Can block thermal short circuits when installed continuously over frames or joists.
Reflective Systems Foil-faced paper Foil-faced polyethylene bubbles Foil-faced plastic film Foil-faced cardboard	Foils, films, or papers: Fitted between wood-frame studs joists, and beams	Unfinished ceilings, walls, and floors	Do-it-yourself All suitable for framing at standard spacing. Bubble-form suitable if framing is irregular or if obstructions are present Effectiveness depends on spacing and heat flow direction
Loose-Fill (poured in) Vermiculite or Perlite	not currently used for home insulation, but may be found in older homes

Your home may have one or more of several different insulation materials.

Mineral fiber insulation, including fiber glass and rock wool, is produced from either molten glass, slag, or rock. Fiberglass insulation is usually very light-weight, and yellow, pink, or white in color. Fiber glass can be found in loose-fill and blanket, either batt or roll, forms. Rock wool loose-fill is usually more dense than fiber glass, and is most commonly gray with black specks. Some rock wool 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, fiber glass, 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.

Compare your findings with recommended levels of insulation.

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