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insulating a block house (want to mount drywall creatively)


bmdavis's Avatar
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Join Date: Apr 2011
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NC

04-02-11, 08:45 PM   #1  
insulating a block house (want to mount drywall creatively)

I am getting ready to completely gut an old concrete block house. I will be removing all interior walls, electrical and plumbing. I want the best insulation I can afford and was thinking I had a creative solution, but not sure how to implement it. I want to use rigid foam (2 layers to decrease airflow). I want to avoid fur strips if possible because of thermal bridging. 2 methods come to mind - 1. mount plywood to one side of the foam board, sort of like 1/2 of a SIP and mount the drywall to the plywood, but I am not sure if that method will be strong enough to support drywall even if the planning department lets me do it. 2. Build studs to mount drywall but use 2x2s so that I can put one layer of foam between the block wall and the 2x2 studs.

Am I wasting to much energy trying to solve an unsolvable problem? Is there a better solution? Any suggestions would be appreciated (I would prefer to look like an idiot here than in the planning dept).

 
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chandler's Avatar
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04-03-11, 03:29 AM   #2  
Welcome to the forums!! You hit on a key.....building department. They would have to approve any such renovation. Doing the XPS thing on the walls would require you tape each joint, and offset your sheetrock from the existing seams for proper rigidity. I doubt the XPS/plywood/sheetrock sandwich would stand up to gravity, though
With block walls, you are getting some insulation via the hollow cores. Framing the walls will allow you to properly insulate, run your plumbing and electrical and give a proper substrate for your wall covering (sheetrock).
You are being creative, don't get me wrong. IMO conventional methods may outweigh creativity when it comes to practicality.
Go to the planning department with a conventional technique, as well as your creative one. See which one they will approve. That way, you will have a sound technique to fall back on and they can't say much about your other one, should they not approve it. Always have Plan B.

 
joecaption's Avatar
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VA

04-03-11, 05:31 AM   #3  
With an unisulated block home your only going to be able to get the wall but so insulated unless you build the wall a full 3-1/2". Thermal bridging will be the least of your problums.
90% of your heat loss is through the ceiling, windows and doors not the walls. If it's on a slab then a lot of cold also comes up through the floors.
What I did on mine was to glue the 3/4" thick foam directly to the block wall, added strips of ripped Advantec subflooring ( used Advantec because it does not split and holds screws well) at the top and bottom and every 24" on the wall with tap con screws in predrill and counter sunk holes in the Advantec.
On the outside of the home I did the same thing except I installed the strips first every 16" then installed the foam between the strips, I installed 1 X 6 vinyl lumber at the bottom of the wall so the weed wacker and the splash back would not hit the siding with a piece of Z moulding on top of the vinyl trim, and vinyl sided over that. I had to build out all of the trim and the sills so when I wrapped it with coil stock the J moulding would not stick out past the trim. So now I have 1-1/2 of foam total and a sided house not ugly block. I also replaced all the window with replacement windows making sure to remove the trim on the inside to be able to insulate the old weight pockets.
Once that was done I insulated to R-50 in the attic. My heating bill went from $300.00 a month to $90.00.

 
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