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Where to Insulate in Your Home

Not sure where exactly to insulate? Probably in more places than you think. All surfaces that separate your home from the outside— attics, walls, basement walls, floors above vented crawl spaces, floors over unheated garages or porches, cathedral ceilings, and knee walls—should be insulated using thermal mineral fiber insulation. All walls, ceilings and floors separating rooms in a home should be insulated using acoustic mineral fiber insulation. The goal is to create a consistent wrap around the home, a “thermal envelope”, with no penetrations.

Not every area is easy to access. Ceilings and attics are always good places to start, both because they are accessible and because more heat escapes through the roof than any other part of the home.

Attics, Flat and Cathedral Ceilings

The most common products for attics and flat ceilings are mineral fiber batts and loose fill insulation. Note that batt products need to have a width matching the full width of your cavities—most usually 16” (41 cm) or 24” (61 cm) wide. This is to be sure that the insulation fills the spaces between the ceiling joists or bottom chords of trusses. The minimum recommended level of insulation is that specified by the ENERGY STAR® program.

Always check the manufacturer’s recommended installation instructions and install the proper amount evenly. Take special care to follow the instructions for installing good air and vapour barriers.

A combination of batts and loose-fill insulation is another alternative. This method is particularly effective in homes with roof trusses or hard-to-reach “nook and crannies”—places that are prime for energy loss.

For cathedral ceilings, check your mineral fibre insulation manufacturer to:

  1. Determine if the slope of your cathedral ceiling is not too steep for loose fill insulation.
  2. Check the exact air gap that is required, and any related ventilation instructions.
  3. Maximize the amount of mineral fiber insulation, which will typically require you to use a high density batt, not loose fill.

Unlike an attic, a cathedral ceiling will not have an access point for adding insulation in the future.


Ideally, basements should be left unfinished for at least one year after construction to allow the concrete to fully dry. Before finishing the basement, check that there are no signs of water damage or cracks. If there are any, get a professional to fix these before starting. For finished basements, standard or high-performance batts can be used depending on the R-value required. Vapour retarders should face heated areas and be covered as soon as possible.


Perhaps the easiest area to overlook for insulation in the home is ductwork. Insulation products—such as fiberglass duct board, duct wrap, and duct liner—are used to increase indoor comfort by delivering heated and cooled air from room-to-room at design temperatures, controlling condensation, and abating sound, such as cross talk heard between two rooms or HVAC equipment noise. Seal all the duct joints before insulating the ducts, and take care that the insulation does not impede the use of the balancing controls.

Fiberglass duct board is 1”, 1 ½”, or 2” thick rigid boards of insulation manufactured from resin-bonded inorganic glass fibers. This bonding keeps the fibers in place throughout the life of the installation.

Fiberglass duct liner is a thermal and acoustical insulation applied to the inside of sheet metal ducts. These insulation products have coated or mat-faced airstream surfaces designed to resist damage during installation, in service, and during cleaning.

Fiberglass duct wrap is a flexible, resilient blanket which is applied to the exterior of sheet metal ducts. It can be easily cut and fitted to achieve a neat, thermally effective exterior insulation blanket over rectangular, round, oval, or irregularly shaped duct surfaces.

Easily Overlooked Areas

To achieve maximum thermal efficiency, it is important to insulate a space where energy can be lost and comfort can be compromised. Before insulating, make sure that any penetrations in the air barrier are sealed with the appropriate tape or bead product. The following areas are often overlooked:

  • Walls between living spaces and unheated garages, dormer walls, portions of walls above ceilings or adjacent lower sections of split-levels
  • Kneewalls of attic spaces finished as living areas
  • Sloped walls and ceilings of attic spaces finished as living areas
  • Floors over unheated or open spaces, such as garages, porches, unconditioned basements, or cantilevered floors
  • Sidewalls where plumbing fixtures are to be placed must be insulated before the fixtures are installed
  • Openings through building sections: where pipes, wiring, or ductwork penetrate a building section, insulation should be packed tightly into the openings to reduce air infiltration or use caulk to seal the holes
  • Junction boxes for wall switches and convenience outlets at outside walls should be insulated between the rear of the box and the sheathing