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Ptron 02-08-2010 01:07 PM

Options for insulating a concrete block house
 
I have a small, 1 story, < 800sqft, house from the 1940's that I was surprised to discover is constructed from concrete block. The exterior appears to be aluminum over wood siding. The interior is plaster over drywall (about an inch thick total) mounted to 1x4 studs, which are nailed to the concrete blocks. I live in Wisconsin and during the deeper freezes the walls get cold. So I guess I need to explorer what the practical options for insulation are.


Insulating the interior - This doesn't seem like a good possibility to me. The gap between the drywall and block is only 3/4" so blown in insulation seems like a waste of time, if it's even possible. Tearing down the walls and building them out is a deal breaker, not only because of the work but also because the house is already too small to lose any more interior space, even if it's only a few inches all the way around.


Insulating the blocks - I was actually sort of keen on the idea of blowing insulation into the concrete block cavities. Despite having to drill a few hundred holes, it still seems like the least amount of work. The big plus of this method is if the cavities are open all the way down through the foundation, it would insulate the basement walls as well. However, I've come to understand it's not very effective as most of the cold is transferred through the solid parts of the block.


Insulating the exterior - probably what has to happen, ultimately. The obvious downside is having to re-side the house. Not something I was looking forward to doing. Another thing is, doesn't it take several inches of foam to get to R-19? I'd have to find some way to expand the external structure of the house. What a royal PITA. Also there is the couple feet of basement that is above ground and wouldn't be covered by the siding/insulation.


Maybe some combination of external insulation and insulating the blocks would be worth considering? Or even all three if I blew in a layer in the 3/4" interior gap. Any advice on this would be appreciated.

Summiteer 03-26-2010 09:37 PM

I too have the same dilemma as you so any help would be great. I am lucky enough to be redoing my siding anyway, I'm just wondering if there are any alternatives to foam, like R19 fiberglass with 2x6's attached to the blocks.

So here's a bump in hopes that we get an answer. :thumbup:

Ptron 03-27-2010 12:05 AM

Heh. I forgot I posted this. Thanks for the bump.

Here's what I've learned since. Unfortunately it's not much. I wasn't finding a real practical solution so I've kind of given up for the moment.

The pink foam sheets they sell at a local big box are R-5/inch. They also sell some panels from Dow called TUFF-R that's compressed fiber glass (or something like that) covered with foil. I think they were R-6/inch. I don't know if there's anything available with a higher R-value/inch that's practical.

I got a quote from a company that was going to spray a liquid foam on the outside but I still would have had to pull the siding. I think it has a really high R-value as they were quoting for 2.5" thick. If that's for R-19 then thats R-7.6/inch. Unfortunately, it's really expensive ( a little over 2 grand for ~1000 sqft. ) and I can't expand the outside of my house that much since my roof already barely has any overhang.

It's also apparently really important to have a vapor barrier in the right spot. It's my understanding it varies with climate and that in a cold climate (like southern Wisconsin where I live) it should go right under the drywall. Again, ripping down all that plaster, drywall, trim, etc...probably not happening. I've heard they make a vapor barrier paint but I don't know anything about it.

If you can find a structurally sound way to use 2x4 studs on the outside of your house, then I suppose that's 3-1/2 of space for panels which would get you pretty close to R-19. ...And maybe then you could put the vapor barrier between the blocks and the panels/new studs. But that's just a guess. Good luck. I'd appreciate hearing what you decide to do or not do and how it works out. I'll update as I find out more as well.

CrpntrFrk 03-27-2010 12:08 AM

I live in a small town so technological advances are not seen too often here so someone might be able to help you out with the specific insulation to be used. I would go further into investigating insulating the block cells.

The advise I am most certain of is air flow, doors, and windows. Your R-30 walls and ceilings are nothing without good sealing doors and double (maybe triple) pane windows. In my experience with block homes your outlets on exterior walls is also something to investigate. Lots of times you can take off the the outlet cover and feel the draft. Basically make your home air tight. Any where the is an air leak you are losing energy.

Ptron 03-27-2010 12:15 AM

Oh, and the gist of the vapor barrier thing is that it has to be within the freezing point of the wall (does that make sense) or you get freezing moisture inside your walls. What I don't know is what happens when you don't have a vapor barrier. I would guess then that without a vapor barrer you don't get a buildup of moisture that freezes? But why then is it so important to have?

Ptron 03-27-2010 12:22 AM

Quote:

Originally Posted by CrpntrFrk (Post 420210)
In my experience with block homes your outlets on exterior walls is also something to investigate. Lots of times you can take off the the outlet cover and feel the draft.

Ahh, bingo. They knocked holes into the cavities of the blocks for the outlet boxes to set into and yes they are drafty and cold. Should I maybe stuff the cavities behind the boxes with insulation? I'm going to replace the boxes anyway as I get rid of the knob and tube wiring.

CrpntrFrk 03-27-2010 12:31 AM

Quote:

Originally Posted by Ptron (Post 420214)
Ahh, bingo. They knocked holes into the cavities of the blocks for the outlet boxes to set into and yes they are drafty and cold. Should I maybe stuff the cavities behind the boxes with insulation? I'm going to replace the boxes anyway as I get rid of the knob and tube wiring.

You can but I prefer spray foam. The yellow stuff is great. Be careful because it will expand fast, it will be very messy, and it is not easy to clean up. On the other hand the make a white spray foam that will not expand as much, as fast, can be tooled, and cleaned up with water.

Be sure not to use the yellow stuff around any doors because when it expands it is so powerful that it could affect the operation of the door.

McK595 04-05-2010 03:55 PM

I also have a non-insulated block home but live in the Southeast. Currently I have aluminum siding with wood trim, the siding looks cheap/dated and the wood is rotting. I am trying to figure best options for insulating and re-siding with Hardiboard.

One thing that is different between a block home with plaster walls and a traditional framed home is the amount of thermal massing. The mass of the block and plaster is substantially more than framing and sheetrock so that helps regulate swings in temperature. So though the R-value is low you can still achieve a good comfort level by reducing air penetrations using caulk and foam to seal all leaks around bottom plates, outlets and any floor or ceiling penetrations, then the home is at least not "drafty." I also put in new vinyl windows which help tremendously.

Anyhow, what I am getting at is I think in my application being in the SE that focusing on making the house "tight" is more important than adding a lot of insulation, especially since I also have very minimal overhangs. What I am considering doing is removing all the siding and trim, wrapping the home in a high quality house wrap with a radiant barrier, adding 3/4" furring strips (rip pressure treated plywood into 2.5" strips) to all the walls then attaching the siding to the furring strips. Can not decide if I should just leave a 3/4" air gap (which also gives a small R-Value) between the siding and housewrap (Tyvek Thermawrap) as a drainage plane (would put screen at top and bottom to keep out bugs and debris) or to put 3/4" rigid insulation in the gaps. Would be interested to hear what people think. Thinking you could do the same thing with 2x4 furring strips and use thicker foam board but would be really important to fit the foam tightly between the furring strips and maybe even caulk those joints.


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