Is there an expandable foam insulation that would insulate exterior walls consisting of 2 brick layers with 1" hollow space between?


Is there an expandable foam insulation that would insulate exterior walls consisting of 2 brick layers with 1" hollow space between?

Asked by Onie

The house was built in the '20's and has no studs on any exterior walls and therefore no insulation. We are looking for a way to insulate it without losing 4" interior space on all exterior walls and to avoid replacing all interior trim.

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Michael Holcomb's picture

The limitations you set significantly limit the potential ways to insulate the walls in your home.

  • The 1-inch space limits the amount of insulation that can be installed so you will want to make certain you install the best performing material.
  • It wouldn't make any sense to install a fibrous material in this space since it does not stop convection.
  • Some expansive foam insulation will provide you with maximum R-value for this space and reduce drafts.

There are a variety of foam insulation materials designed to be injected into existing wall cavities. Many of these injectable foams have problems with severe shrinkage over a short period of time. We have seen shrinkage between 1 and 5 inches within the first year. Many of the problems we see are with the material itself.

Spray polyurethane foam

If you can find a qualified contractor you might consider a spray polyurethane foam insulation. These long chain polymers are thermoset plastic when fully cured and do not shrink.

  • Icynene is a spray polyurethane foam that can be injected into a wall cavity.
  • Many contractors will not attempt it because of the potential for causing damage to the structure if the foam expands to quickly.
  • There may be less potential for problems when injecting between two course of brick than between brick and interior drywall or plaster.

Another potential problem with a product like Icynene is moisture. Since it is an open-cell foam, wicking may be a problem.

  • Connecting the brick walls may encourage water to travel from the outside to the interior.
  • Discuss these issues and choose your contractor carefully and see if you are comfortable with the risk level involved with this insulation.

Polystyrene beads

One other option you might want to consider is polystyrene beads. The beads are installed dry and may reduce any potential for wicking.

  • Since there is no expansion there is no danger of damaging the structure.
  • This material is easier to install and costs less.
  • It is not as energy efficient as Icynene.

Most commercial contractors have used this method to insulate masonry block building, literally pouring the material into the block cavities after the top course was set.

These beads offer minimal R-value and little air barrier characteristics.

Best of luck.