Types of insulation

Insulation slows heat moving through the parts of a house that touch the outdoors or an unheated space: the attic floor, the outside walls and the floor over a crawl space. In summer it keeps heat out. In winter it keeps heat in. In both seasons, it means your heating and cooling system runs less.

Homeowners mostly see three kinds: blown-in (loose-fill), batts and spray foam. Each one suits different spots in the house. This guide explains what they are, where each one makes sense and how to read the R-value on the label. To price adding insulation, see attic insulation and ventilation and crawl space floor insulation.

What R-value means

R-value is a number that measures how well insulation resists heat flow. The higher the number, the better it insulates [1].

Two things to know:

R-value adds up with depth. Twice as much of the same insulation gives about twice the R-value. That's why attic insulation is measured in inches.
Materials differ per inch. ENERGY STAR's rule of thumb for estimating what's in your attic is about R-2.5 per inch for loose fiberglass, R-2.8 for loose rock wool, R-3.7 for loose cellulose and R-3.2 for fiberglass batts [2]. So 10 inches of blown cellulose insulates more than 10 inches of blown fiberglass.

Manufacturers have to label insulation packages with the R-value, and installers and retailers have to give you a fact sheet, under a Federal Trade Commission rule [3]. Ask your installer for it.

Blown-in (loose-fill) insulation

Blown-in insulation is small pieces of fiberglass, cellulose (mostly recycled paper) or mineral wool that a machine blows into place [4]. It fills around wires, pipes and odd-shaped framing without gaps.

Where it's used:

Open attic floors. This is the most common way to add insulation to an existing attic. It can go right on top of old batts or old loose-fill [5].
Closed walls. In a finished home, installers can blow insulation into empty wall cavities through small holes that are patched afterward [4].

Good to know: It needs a blowing machine. ENERGY STAR notes it may be wise to hire a professional for loose-fill, though some stores rent machines [5]. Loose-fill also needs to be spread evenly with no low spots [5].

Batts and rolls

Batts are the pre-cut blankets most people picture, usually fiberglass or mineral wool, sometimes with a paper or foil facing [4]. They're sized to fit between standard studs and joists.

Where they're used:

Open walls in new construction or during a remodel. A 2x4 wall usually takes R-13 or R-15 batts, and a 2x6 wall takes R-19 or R-21 [4].
Floors over crawl spaces, held up between the joists with wire supports or straps. Batts that aren't supported tend to sag and fall over time. See floor insulation that has fallen.
Attics, laid between and across the ceiling joists.

Good to know: If you lay batts over existing loose-fill in an attic, they must be unfaced, with no paper or foil backing [5]. Batts work best when they're cut to fit snugly, with no gaps.

Spray foam

Spray foam is a liquid that expands and hardens in place. A professional installer usually applies it with special equipment [4]. It fills gaps and also seals air leaks, which batts and loose-fill don't do on their own [4].

There are two main types [6]:

	Open-cell	Closed-cell
R-value per inch	About R-3.6	About R-6
Weight	Light and soft	About four times denser, rigid
Moisture	Lets water vapor pass	Acts as a vapor retarder
Common uses	Walls, rooflines	Rim joists, foundation walls, rooflines

Where it's used: wall cavities, rim joists (the band of framing where the floor meets the foundation), the underside of the roof deck, and crawl space walls. Foam sprayed on the underside of the roof deck is a different approach from insulating the attic floor, and it changes how the attic handles heat and moisture. Ask the installer how it will work with your roof and attic vents.

Good to know: The EPA advises everyone except the properly protected installers to leave the home while spray foam is applied, and to stay out until it has cured. Curing time depends on the product, so ask the installer before the job how long you'll need to be out [7]. Spray foam usually costs more than batts or blown-in.

Other types you may run into

Rigid foam board. Stiff panels of polystyrene or polyisocyanurate, with a high R-value for their thickness [4]. Used on foundation and crawl space walls and under siding. Indoors it has to be covered with half-inch drywall or another approved material [4].
Radiant barrier. Foil sheeting, usually in attics, that reflects heat rather than slowing it like insulation. The Department of Energy says it can cut cooling costs 5 to 10 percent in warm, sunny climates [4].
Vermiculite. Older homes may have pebble-like, gray-brown or silver-gold loose-fill in the attic. The EPA says to assume vermiculite contains asbestos and not to disturb it. Don't store things in that attic or try to remove it yourself. Hire a professional asbestos contractor if work would disturb it [8].

Which type goes where

Part of the house	Usual choice for an existing home
Open attic floor	Blown-in on top of what's there
Finished walls	Blown-in through small holes
Open walls during a remodel	Batts or spray foam
Floor over a vented crawl space	Batts held up with supports
Sealed (encapsulated) crawl space	Rigid foam or spray foam on the walls
Rim joists	Spray foam or rigid foam

If your crawl space is being sealed, the insulation usually moves from the floor to the walls. See vapor barrier vs. encapsulation.

How much do you need?

ENERGY STAR's recommended levels depend on your climate zone [9]. For an attic with little or no insulation, it recommends R-49 in Zones 2 and 3 and R-60 in Zone 4. The Atlanta area is Zone 3 [10]. The Dallas-Fort Worth area falls in Zone 2 or 3 depending on the county, and the recommendation is the same for both [12]. North Carolina's Piedmont, including Raleigh-Durham, Charlotte and Greensboro, sits near the line between Zones 3 and 4, and the line has shifted as maps are updated [11]. R-49 is about 20 inches of loose fiberglass or 13 inches of loose cellulose, using ENERGY STAR's per-inch figures [2].

Quick check: if your attic insulation is level with or below the tops of the ceiling joists, you probably need more [2]. A HomeCloud evaluation notes insufficient attic insulation depth and missing attic insulation.

Before adding insulation, seal air leaks into the attic and fix any roof leaks, wet spots or mold. New insulation over a moisture problem hides it.

HomeCloud is a licensed general contractor. We evaluate homes and price and do the repairs, including insulation work.