AJL lives in a 1920s house in southwestern Michigan built with decorative concrete block—a house now due for an insulation upgrade.
“The interior walls are comprised of vertical furring nailed into inserts in the mortar joints and horizontal lath nailed to the furring strips and plaster,” AJL writes in this recent Q&A post. “I have insulated the core of the block walls by injecting foam.”
AJL plans to remove the interior plaster, and possibly the lath, then frame 2×4 walls, rewire, insulate, and install drywall. “I understand the concern with condensation and moisture,” he says, “and I want to make sure I am planning and executing this job correctly.”
This approach would leave the exterior of the building untouched. Is there a better way? That’s the topic for this Q&A Spotlight.
The insulation should be on the exterior
Insulating the interior will reduce heat loss but it also will mean the block walls are no longer warm, Kyle Bentley points out, and that could mean a higher risk of moisture damage. AJL would be better off insulating the outside of the building, and by skipping a new 2×4 interior wall AJL also would be picking up a little extra space.
“Kyle is probably right about insulating the exterior being better,” Bill Wichers adds. “I would not frame out a regular stud wall on the interior, either, since it doesn’t really gain you anything. I would try insulating the outside using rigid foam, at least 2 in. of polyiso. You could put your exterior cladding right over that, or add furring strips, depending on what you want to use.”
On the inside, Wichers says, AJL could use 2x3s on the flat to create vertical channels for wiring. “You can use 4-in.-square 1-1/2-in.-deep boxes (which are standard), mounted…
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