Roof and Attic Insulation Materials for Minnesota Homes

Attic insulation is critical to the energy efficiency of your home. The Department of Energy estimates that a properly insulated attic can shave 10 to 50 percent off your winter heating and also save you substantial money on your summer AC bill. Here in Minnesota, we get both extreme winters and hot summers, so roof insulation is more important here than in more temperate regions.

Insulation may be installed in on the roof itself or on the attic floor. Your type of roof or attic may be the determining factor on this, or you may have the option for either or both types.

Roof-Level Insulation

Generally, roof insulation has more benefits and higher overall performance than attic-floor level insulation. Installing insulation at the roof level has several benefits can help to stop air leaks, which drain heat and create uncomfortable drafts. It is possible to use fiberglass batt insulation between attic rafters to insulate cathedral type ceilings and attic roofs, this technique isn’t as effective as the foam insulation on the actual roof because fiberglass insulation can compress and lose R-value, and it’s also unable to stop air from leaking out of or into your house compared to rigid foam boards and spray foam insulation.

Types of Foam Insulation

  • Rigid foam insulation: Rigid foam comes in sheets or panels in a variety of thicknesses. When used as attic roof insulation, rigid foam can be installed between attic rafters, directly beneath attic rafters, or in both locations. It has an excellent R-value, which will not change due to compression, and is effective at preventing leaks.
  • Spray foam: Spray Polyurethane Foam (SPF), is normally applied in the space between attic rafters to act as a moisture barrier and leak barrier. It also has an excellent R-value. For both new construction or a remodel of an attic-type living space, this is a great option.
  • A Combination of Fiberglass and foam: Both materials may be installed together, providing effective attic roof insulation. The fiberglass batts would be installed normally, between attic rafters, and a thin layer of rigid foam is fastened to the bottom edges of attic rafters for a one-two punch.

Floor Level DIY Insulation Options

A loose fill of fiberglass, cellulose, or Mineral Wool may be blown into the space or you can pour the insulation into the cavity and spread it manually.
• Batts of the same above materials, plus cotton, is most often packaged in rolls that come in various thicknesses and standard widths, usually 16 inches and 24 inches, to fit between joists or studs in a house’s framing. They come with or without a paper or foil facing that acts as a vapor barrier. You add one or more layers to achieve the desired level of insulation.

When insulating your home, you can choose from many types of insulation. To choose the best type of insulation, you should first determine the following:

  • Where you want or need to install/add insulation
  • The recommended R-values for areas you want to insulate

roof and attic insulation in minnesota home

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.

Type Insulation Materials Where Applicable 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 of 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.