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Insulating Cement Block Walls

10 years ago

Several months ago we purchased a house that was constructed in the 50's. We are in love with the house, but it has one significant heating problem - all of the external walls are cement block. The cement block you see on the inside of the house is the interior surface of the same cement block you see on the exterior of the house. Needless to say, there isn't much insulating value in the external walls and we don't want to go broke paying to heat the outdoors any longer in the winter. The building plans say there is insulation in the block cavities, but we would like to further increase the insulating ability of the exterior walls. The walls in great shape with no cracks and are very airtight.

We've been researching different ways of insulating the walls and what we're thinking of is:

1 - Adhere /glue two inches of extruded polystyrene directly to the interior surface of the external walls and use tuck tape to seal in corners and seams to make it as airtight as possible.

2 - Frame-out the walls with 2X4's, connecting the sole plate to the subfloor and the header to the ceiling rafters (not connect the framing to the cement wall, but instead "float" it in front of the polystyrene).

3 - Cut and install polystyrene "inserts" between the framing members to further increase the insulating value of the wall. We were looking at using polystyrene to get the maximum amount of insulating value (instead of using fiberglass batting between the framing timber).

4 - Install a vapor barrier over top of the framing (probably six mil polyethylene sheeting)

5 - Drywall over the framing to create the new interior wall.

We know we will lose several inches of space on the exterior walls, but the rooms are large enough (the smallest bedroom is 15' X 16') that we don't think the loss of space will be a significant issue for us.

Along with the wall insulation, we are having the single-pane windows that are original to the house removed and having Marvin Integrity Ultrex wood-clad (fiberglass exterior, wood interior) installed at the same time and are in talks with the Marvin installers on how to handle the increased thickness of the walls for the windows.

Does this sound like a reasonable approach or are we insane for trying to increase the insulating value of the walls this way?

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Comments (3)

boops2012
10 years ago
You don't indicate what part of the country you are located but with energy costs rising ,I would consider insulating a must. I live in a block home built in 57. Central Florida. Decided to pull off the plasterboard to insulate properly. Behind the board there was a 1x 2 and no insulation, just an air space. Rather than reframe ,we used the polystyrene foam boards cut to fit snugly. Our electric bill is $70 less than the previous year. We also took the opportunity to add a higher r value insulation in the ceiling space. Also made sure to seal around the windows as well.
MokiDogTenSur
Original Author
10 years ago
Ahhh - good point about our location! We're in northern Michigan here.

We've also added insulation in the attic spaces to bring it up to a minimum of R-50.
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worthy
10 years ago
According to the US Department of Energy, there is a mere 3.5 year simple payback period for moving from the Michigan Uniform Energy Code to the International Energy Conservation Code 2012.

Since your home probably doesn't come close to meeting the current state Code, your payback period could be shorter, especially if you're able to do much or all of the work yourself.

Michigan ranges from zone 4 to the northernmost part of the Upper Peninsula in Zone 7. (See the table below for IECC insulation requirements. ) In addition to increasing insulation levels, you need to take measures to tighten the envelope with caulking and insulating or isolating HVAC in unconditioned portions of your home.

Before losing interior space, consider adding insulation to the exterior walls, then siding. This will likely be much more thermally efficient and straightforward than an inside addition that will require framing, moving all wiring and perhaps plumbing, trimwork, drywall and painting. Since you're getting new windows, you can move them to the new exterior plane.

Whichever side you're insulating,, don't overlook the need for better ventilation, possibly with an HRV (heat recovery ventilator) or (energy recovery ventilator) ERV. As well, consider the need for direct vent water heater and furnace systems.

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