Installing Insulation
The maximum thermal performance or R-value of insulation is very dependent on proper installation. Homeowners can install some types of insulation -- notably blankets and materials that can be poured in place. Other types require professional installation.
When hiring a professional certified installer:
- Obtain written cost estimates from several contractors for the R-value you need, and don't be surprised if quoted prices for a given R-value installation vary by more than a factor of two.
- Ask contractors about their air-sealing services and costs as well, because it’s a good idea to seal air leaks before installing insulation.
To evaluate blanket installation, you can measure batt thickness and check for gaps between batts as well as between batts and framing. In addition, inspect insulation for a tight fit around building components that penetrate the insulation, such as electrical boxes. To evaluate sprayed or blown-in types of insulation, measure the depth of the insulation and check for gaps in coverage.
If you choose to install the insulation yourself, follow the manufacturer’s instructions and safety precautions carefully and check local building and fire codes. Do-it-yourself instructions are available from the fiberglass and mineral wool trade group. The cellulose trade group recommends hiring a professional, but if there isn’t a qualified installer in your area or you feel comfortable taking on the job, you may be able to find guidance from manufacturers.
The table below provides an overview of most available insulation materials, how they are installed, where they're typically installed, and their advantages.
Types of Insulation
|
Type |
Installation Method(s) |
Advantages |
||
|
Blanket: batts and rolls |
•Fiberglass •Mineral (rock or slag) wool •Plastic fibers •Natural fibers |
•Unfinished walls, including foundation walls •Floors and ceilings |
Fitted between studs, joists, and beams. |
Do-it-yourself. Suited for standard stud and joist spacing that is relatively free from obstructions. Relatively inexpensive. |
|
Concrete block insulation and insulating concrete blocks |
Foam board, to be placed on outside of wall (usually new construction) or inside of wall (existing homes): Some manufacturers incorporate foam beads or air into the concrete mix to increase R-values |
•Unfinished walls, including foundation walls, for new construction or major renovations •Walls (insulating concrete blocks) |
Require specialized skills
Insulating concrete blocks are sometimes stacked without mortar (dry-stacked) and surface bonded. |
Insulating cores increases wall R-value. Insulating outside of concrete block wall places mass inside conditioned space, which can moderate indoor temperatures. Autoclaved aerated concrete and autoclaved cellular concrete masonry units have 10 times the insulating value of conventional concrete. |
|
Foam board or rigid foam |
•Polystyrene •Polyisocyanurate •Polyurethane |
•Unfinished walls, including foundation walls •Floors and ceilings •Unvented low-slope roofs |
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 weatherproof facing. |
High insulating value for relatively little thickness. Can block thermal short circuits when installed continuously over frames or joists. |
|
Insulating concrete forms (ICFs) |
•Foam boards or foam blocks |
•Unfinished walls, including foundation walls for new construction |
Installed as part of the building structure. |
Insulation is literally built into the home's walls, creating high thermal resistance. |
|
Loose-fill and blown-in |
•Cellulose •Fiberglass •Mineral (rock or slag) wool
|
•Enclosed existing wall or open new wall cavities •Unfinished attic floors •Other hard-to-reach places |
Blown into place using special equipment, sometimes poured in. |
Good for adding insulation to existing finished areas, irregularly shaped areas, and around obstructions. |
|
Reflective system |
•Foil-faced kraft paper, plastic film, polyethylene bubbles, or cardboard |
•Unfinished walls, ceilings, and floors |
Foils, films, or papers fitted between wood-frame studs, joists, rafters, and beams. |
Do-it-yourself. Suitable for framing at standard spacing. Bubble-form suitable if framing is irregular or if obstructions are present. Most effective at preventing downward heat flow, effectiveness depends on spacing. |
|
Rigid fibrous or fiber insulation |
•Fiberglass •Mineral (rock or slag) wool |
•Ducts in unconditioned spaces •Other places requiring insulation that can withstand high temperatures |
HVAC contractors fabricate the insulation into ducts either at their shops or at the job sites. |
Can withstand high temperatures. |
|
Sprayed foam and foamed-in-place |
•Cementitious •Phenolic •Polyisocyanurate •Polyurethane |
•Enclosed existing wall •Open new wall cavities •Unfinished attic floors |
Applied using small spray containers or in larger quantities as a pressure sprayed (foamed-in-place) product. |
Good for adding insulation to existing finished areas, irregularly shaped areas, and around obstructions. |
|
Structural insulated panels (SIPs) |
•Foam board or liquid foam insulation core •Straw core insulation |
•Unfinished walls, ceilings, floors, and roofs for new construction |
Construction workers fit SIPs together to form walls and roof of a house. |
SIP-built houses provide superior and uniform insulation compared to more traditional construction methods; they also take less time to build. |
Blanket: Batt and Roll Insulation
Blanket insulation -- the most common and widely available type of insulation -- comes in the form of batts or rolls. It consists of flexible fibers, most commonly fiberglass. You also can find batts and rolls made from mineral (rock and slag) wool, plastic fibers, and natural fibers, such as cotton and sheep's wool. Learn more about these insulation materials.
Batts and rolls are available in widths suited to standard spacing of wall studs, attic trusses or rafters, and floor joists: 2 inch x 4 inch walls can hold R-13 or R-15 batts; 2 inch x 6 inch walls can use R-19 or R-21 products. Continuous rolls can be hand-cut and trimmed to fit. They are available with or without facings. Manufacturers often attach a facing (such as kraft paper, foil-kraft paper, or vinyl) to act as a vapor barrier and/or air barrier. Batts with a special flame-resistant facing are available in various widths for basement walls and other places where the insulation will be left exposed. A facing also helps facilitate fastening during installation. However, unfaced batts are a better choice when adding insulation over existing insulation.
Standard fiberglass blankets and batts have a thermal resistance or R-value between R-2.9 and R-3.8 per inch of thickness. High-performance (medium-density and high-density) fiberglass blankets and batts have R-values between R-3.7 and R-4.3 per inch of thickness. See the table below for an overview of these characteristics.
Fiberglass Batt Insulation Characteristics
This table is for comparison of fiberglass batts only. Determine actual thickness, R-value, and cost from manufacturer and/or local building supplier.
|
Thickness (inches) |
R-Value |
Cost (cents/sq. ft.) |
|
3 1/2 |
11 |
20-30 |
|
3 5/8 |
13 |
25-35 |
|
3 1/2 (high density) |
15 |
50-60 |
|
6 to 6 1/4 |
19 |
30-40 |
|
5 1/4 (high density) |
21 |
60-70 |
|
8 to 8 1/2 |
25 |
60-70 |
|
8 (high density) |
30 |
70-80 |
|
9 1/2 (standard) |
30 |
70-80 |
|
12 |
38 |
80-90 |
Foam Board or Rigid Foam
Foam boards -- rigid panels of insulation -- can be used to insulate almost any part of your home, from the roof down to the foundation. It is very effective in exterior wall sheathing, interior sheathing for basement walls, and special applications such as attic hatches. Foam insulation R-values range from R-4 to R-6.5 per inch of thickness, which is up to 2 times greater than most other insulating materials of the same thickness. They provide good thermal resistance, and reduce heat conduction through structural elements, like wood and steel studs. The most common types of materials used in making foam board include polystyrene, polyisocyanurate (polyiso), and polyurethane.
Loose-Fill and Blown-In Insulation
Loose-fill insulation consists of small particles of fiber, foam, or other materials. These small particles form an insulation material that can conform to any space without disturbing structures or finishes. This ability to conform makes loose-fill insulation well suited for retrofits and locations where it would be difficult to install other types of insulation.
The most common types of materials used for loose-fill insulation include cellulose, fiberglass, and mineral (rock or slag) wool. All of these materials are produced using recycled waste materials. Cellulose is primarily made from recycled newsprint. Most fiberglass contains 20% to 30% recycled glass. Mineral wool is usually produced from 75% post-industrial recycled content. The table below compares these three materials.
Recommended Specifications by Loose-Fill Insulation Material
|
|
Cellulose |
Fiberglass |
Rock Wool |
|
R-value/inch |
3.2–3.8 |
2.2–2.7 |
3.0–3.3 |
|
Inches (cm) needed for R-38 |
10–12 (25–30) |
14–17 (35–43) |
11.5–13 (29–33) |
|
Density in lb/ft3 (kg/m3) |
1.5–2.0 (24–36) |
0.5–1.0 (10–14) |
1.7 (27) |
|
Weight at R-38 in lb/ft2 (kg/m2) |
1.25–2.0 (6–10) |
0.5–1.2 (3–6) |
1.6–1.8 (8–9) |
|
OK for 1/2" drywall, 24" on center? |
No |
Yes |
No |
|
OK for 1/2" drywall, 16" on center? |
Yes |
Yes |
Yes |
|
OK for 5/8" drywall, 24" on center? |
Yes |
Yes |
Yes |
Some less common loose-fill insulation materials include polystyrene beads and vermiculite and perlite. Loose-fill insulation can be installed in either enclosed cavities such as walls, or unenclosed spaces such as attics. Cellulose, fiberglass, and rock wool are typically blown in by experienced installers skilled at achieving the correct density and R-values. Polystyrene beads, vermiculite, and perlite are typically poured.
Radiant Barriers and Reflective Insulation Systems
Unlike most common insulation systems, which resist conductive and sometimes convective heat flow, radiant barriers and reflective insulation work by reflecting radiant heat away from the living space. Radiant barriers are installed in homes -- usually in attics -- primarily to reduce summer heat gain, which helps lower cooling costs. Reflective insulation incorporates radiant barriers -- typically highly reflective aluminum foils -- into insulation systems that can include a variety of backings, such as kraft paper, plastic film, polyethylene bubbles, or cardboard, as well as thermal insulation materials.
Radiant heat travels in a straight line away from any surface and heats anything solid that absorbs its energy. When the sun heats a roof, it's primarily the sun's radiant energy that makes the roof hot. A large portion of this heat travels by conduction through the roofing materials to the attic side of the roof. The hot roof material then radiates its gained heat energy onto the cooler attic surfaces, including the air ducts and the attic floor. A radiant barrier reduces the radiant heat transfer from the underside of the roof to the other surfaces in the attic. To be effective, it must face an air space.
Radiant barriers are more effective in hot climates, especially when cooling air ducts are located in the attic. Some studies show that radiant barriers can lower cooling costs 5% to 10% when used in a warm, sunny climate. The reduced heat gain may even allow for a smaller air conditioning system. In cool climates, however, it's usually more cost-effective to install more thermal insulation.
Sprayed-Foam and Foamed-In-Place Insulation
Liquid foam insulation materials can be sprayed, foamed-in-place, injected, or poured. Foam-in-place insulation can be blown into walls, on attic surfaces, or under floors to insulate and reduce air leakage. Some installations can have twice the R-value per inch of traditional batt insulation, and can fill even the smallest cavities, creating an effective air barrier. You can use the small pressurized cans of foam-in-place insulation to reduce air leakage in holes and cracks, such as window and door frames, and electrical and plumbing penetrations.
