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How to Insulate External Walls

Updated February 21, 2017

External walls lose a lot of heat, so choose your insulation carefully. Fibreglass and mineral fibre insulation come in batts or rolls. They are easy to install, but not the best for filling irregular spaces. Cellulose thermal insulation is loose-fill, so it fills any cavity uniformly, but it might be best to have a professional install it with a special blower. There are two types of vermiculite insulation, both easy to install. Treated vermiculite is water repellent; untreated vermiculite is not. Rigid foam insulation boards are great for small spaces. Urethane foam comes in boards or can be sprayed in place.

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  1. Don protective goggles and a dust mask.

  2. Remove panelling, drywall or other wall coverings from the external walls.

  3. Cut the insulation to size for each gap between the wall studs. Typically, a utility knife works best, but follow the manufacturer's installation recommendations.

  4. Place the insulation in the gaps. The goal is to install it so that it fills every gap completely. Do not compress the insulation or force it into a space that is too small, as doing so decreases the insulation’s effectiveness. Pay careful attention to common problem areas, such as near windows, outlets and ceiling joists.

  5. Close the wall by installing wallboard or another wall covering.

  6. Rent or buy a blower at a tool rental or home-improvement store. Some loose-fill insulation comes in bags that you can pour into gaps, but you may have difficulty achieving the recommended density and coverage if you don't use a blower.

  7. Install insulation according to the manufacturer’s recommendations. Typically, you will cut a hole in the wall and blow loose-fill insulation into the walls until all empty spaces are full. The recommendations will explain how to determine when you have achieved the perfect density. Don’t leave any gaps empty, or your wall will be draughty. The goal is to uniformly fill all gaps in order to prevent drafts and loss of heat.

  8. Close the wall with wallboard or another covering.

  9. Rent or buy a sprayer. Remove panelling, drywall or other coverings from the external wall.

  10. Spray the gaps between the studs. Allow the foam to expand, then trim it back with a utility knife so that the insulation is flush with the wall studs. When you finish, all spaces should be entirely filled with insulation.

  11. Close the wall with wallboard or other covering.

  12. Tip

    Insulation’s “R-value” indicates its effectiveness. The higher the R-value, the better it insulates your wall. Choose the insulation that works best for your climate and budget.

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Things You'll Need

  • Utility knife
  • Blower or sprayer

About the Author

Stan Mack is a business writer specializing in finance, business ethics and human resources. His work has appeared in the online editions of the "Houston Chronicle" and "USA Today," among other outlets. Mack studied philosophy and economics at the University of Memphis.

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