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How to Insulate a Wall

Insulating walls is quite an easy task. All you need is a batt of insulation material usually made of fiber glass that you could simply cut and fill the spaces in your wall frames. In case, you are dealing with external walls that may already be insulated or have several plumbing and electricity lines running through them, you could opt for a loose fill insulation or foam based insulation that can be blown or pumped into the empty spaces in your wall. If you are looking to insulate a concrete wall that has no studs, you could simply prepare a wooden frame, fasten it to your wall and go ahead stapling the cut batt pieces into position. Here’s how you can try a simple wall insulation. Check with your local energy agencies for the R-value of the insulation that most suits your region.

Complexity Level: Basic

Time Required: 3-4 hours for about 250 sq.ft

Resources Required:

  1. Insulation batt/loose fill insulation
  2. Utility knife
  3. Protective gear (goggles, dust mask, gloves, long-sleeved work outfit, working shoes)
  4. Staple Gun


1. Complete one round of basic checks

  • Check the walls for existing insulation, position of studs, water seepage, plumbing, electricity wiring, light fixtures and heat sources.
  • Correct water seepage problems and allow the surface to dry before proceeding with insulation.
  • Decide whether you would need a batt or loose filler installation, depending on the wall structure. Prepare a wooden frame if you are dealing with a concrete wall.

2. Prepare the insulation medium

  • Go for a batt with a width that matches the largest piece of your frame space and a depth of about three inches. Cut the batt such that it fits the empty spaces between the studs on your wall or frame.
  • In case, you plan to blow in a loose filler like cellulose/fiber glass or foam, do prepare the blower/foam sprayer and check if equipment works fine.

3. Insulate the wall

  • Fit the cut insulation batt directly to studs on your wall using the staple gun, driving the staples flat into the surface.
  • If you plan to use a blower or foam sprayer, cut a small hole through the dry wall and spray or blow in the material to fill the empty spaces in the wall. You could fill the hole and smoothen the rough edges once the filling has dried.
  • To insulate a concrete wall, fix the wooden frame to the wall using concrete plugs, and then staple the cut batt to the edges of the frame.
  • Staple the batt face down, with the foiled/papered surface on the outside. As the treated surface is flammable, seal the insulation with a dry board to complete the process.

Insulating an external wall may be a complex process given the fact that it may contain several hidden water and electrical connections. You could however choose to implement an external sider.

Frequently Asked Questions:

1. How does cavity insulation work?

Several small holes are drilled on the external wall at predefined intervals and the insulation material is blown into the holes using a hose, generating minimum dust in the process. The small holes measuring about 25 mm are then sealed with mortar.

Quick Tips:

  1. If you have chosen to drill holes and blow in the insulation, seal the holes and repaint the exterior for a smooth finish.
  2. You could easily rent a cellulose loose fill sprayer instead of using a foam expander process.
  3. If required, you could also place a vapor barrier between the insulation and the wall, stapling the film tightly at regular 12-inch intervals.

Things To Watch Out For:

  1. Do not apply force, pat or crush the insulation. This will decrease the R-value or heat flow resistance factor of the material.
  2. Check if the insulation is installed with the treated side facing outwards.
  3. Finish the process by covering the insulation with a dry wall, since the foiled/papered side is inflammable.
  4. Opt for a external siding instead of working directly on the external wall.
  5. Seal the frames of window/door and other installation boards with caulking to prevent air leaks.
  6. Allow at least 3 inches distance between a heat/electricity source and the insulation.