Insulation: The Facts Part 2

The Old House Web

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

Topics covered inPart 2: Where should insulation be installed? * Basic Types of Insulation.

Does your home need more insulation?

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

If you don't have someone else inspect your home, you'll need to look forinsulation 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 measurethe thickness of the insulation and identify which type of insulation was used

house insulation

  1. In unfinished attic spaces, insulate between and over the floor joists to seal off living spaces below.*
    1A attic access door
  2. 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.
  3. 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.
  4. 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.
  5. Band joists.
  6. 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





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 fromeither molten glass, slag, or rock. Fiberglass insulation is usually verylight-weight, and yellow, pink, or white in color. Fiber glass can be found inloose-fill and blanket, either batt or roll, forms. Rock wool loose-fill isusually more dense than fiber glass, and is most commonly gray with blackspecks. Some rock wool products, however, are near-white.

Loose-fill celluloseinsulation is commonly manufactured from recycled newsprint, cardboard, or otherforms of waste paper. Most cellulose is in the form of small flat pieces ratherthan fibers. However, some cellulose products are so finely divided they lookfibrous as well. Vermiculite- and perlite-loose-fill products are no longercommonly used as home insulation, but you may find them in an older home. Theyare produced by expanding naturally occurring minerals in a furnace. Theresulting granules are non-combustible and are commonly poured-in-place.

First, check the attic; then check walls and floors adjacent to an unheatedspace 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 toexamine the insulation (if any) and to measure the depth or thickness of theinsulation.

It is more difficult to inspect finished exterior walls. One methodis to use an electrical outlet on the wall, but first be sure to turn off thepower to the outlet. Then remove the cover plate and shine a flashlight into thecrack around the outlet box. You should be able to see whether or not insulationis in the wall. You may need to pull a small amount out to determine which typeof material was used. Also, you should check separate outlets on the first andsecond floor, and in old and new parts of the house, because wall insulation inone wall doesn't necessarily mean that it's everywhere in the house. Analternative to checking through electrical outlets is to remove and then replacea small section of the exterior siding.

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

Compare your findings with recommended levels of insulation.

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To Part 3: Analyzing your findings ->

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