insulating old concrete block house


Old 12-07-04, 08:17 AM
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insulating old concrete block house

We need to do some serious insulation on our concrete block house that was originally build as a summer beach cottage. FYI, we're in Delaware so we do get the cold weather. Here are my questions.

1. Attic: Our furnace is in the attic and all the ductwork runs through the attic (yes, ducts are in the ceiling of our house which doesn't help matters). There is some insulation along the sides (low area) of the attic, none in the middle where you can walk. We know we can put down more insulation on the sides where it's already insulated, but we're not sure if/how to insulate the ducts, and what to do about the center area where we walk. Also, there is wiring running through the side areas on top of some of the existing insulation -- how do I insulate around that??

2. Walls: Right now our interior walls are simply 1x2 firring strips on top of the concrete block, and paneling on top of that. I'm trying to figure out the best way to insulate the walls with a minimal thickness -- I'd love to, for example, put up regular framing and thick bats of insulation between that and drywall on top of that, but that would make us lose about 4" or more on each wall (which is a big deal in a tiny house like ours with its 10x10 bedrooms etc.) plus we'd have to pretty dramatically redo all the windows. This has to be a DIY project!

I was told that there is such a thing as insulating drywall with a vapor barrier on the back but I can't find anything about it at all. That would be ideal for us. I'd love to hear any other suggestions that could allow us to use the current 1x2 firring strips instead of reframing much thicker walls.

Also, will tightening the house like this help wtih the moisture/mold/mildew problems we have? We live in a very humid area, and it seems that no matter how much we run the AC, our closets and other enclosed areas in particular get all mustty and mildewed. I'm hoping that insulating will actually help, and I'm terrified that I'm wrong and that it might actually make it worse!

3. Flooring: I mentioned the ducts in the ceiling. Right now we have "state hospital" old asbestos tile applied directly to a concrete slab. We've been looking at cork or laminates. Someone suggested installing radiant heat under tile instead, but can someone give me an idea of the cost of doing that? I just had a whole new hvac system installed (heat and air) so I can't justify spending a fortune on doing something like this, but I'm open to the idea -- our floors are just wicked cold in the winter.

Thanks for any help and suggestions you can offer!
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Old 12-13-04, 06:24 PM
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I used to teach a codes class. Insulating over the wires is not a problem if the wiring was installed to code in the first place. But you should check with your local codes office. They make a duct wrap for the ducting. Block makes a poor dwelling in most cases! Is your walls really concrete block, or cinder block, which is often called concrete block. Nearly all block will pass water. But real concrete is the best of the lot. Sealing will help, they make products for inside or outside but be sure and get the flexible type, weakest point of a block wall is the grout. That would help with the mold. Also, was the slab installed with a barrier under it. Try taping a square of plastic to the floor and see if moisture collects under it.
My shop 40 x 32 is block, I put 2x4's on 24" centers, and r13 insulation, which was enough for a shop. Not sure r13 would do it were you are. That's the easiest fix. The window's didn't prove to be any problem. Install another set of windows.(the type that open from top or bottom,)
You might think about insulating the outside and stucco it. Most DIY's can handle Stucco, if they take their time, nice part is you can do a little at a time.
Hope that helps.
Old 12-30-04, 06:33 AM
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My experience

I have a house with similar construction in Northern VA. It certainly has been a cold December.

I initially sought to do everything myself but reached the point of diminishing returns. I ended up getting my cinder block filled with core-fill 500 (google it), which brought the R-value up to something like 11. I also had Icynene foam installed in the attic. I have to say that removing the old insulation first is DIY but its a lot of work -- and disposal can be an issue. If you end up removing your old insulation, MAKE SURE you protect yourself. I used the best respirator I could find at Home Depot, a Tyvek suit, and heavy rubber gloves, with the result that I was not discomforted have no health worries about having done this job.

While I can't yet tell you how much energy I'm saving, the house is very much more comfortable, especially in cold and windy weather.

Regardless of what you do, there are some important things to keep in mind. First, insulation is important. But, reducing air infiltration is probably of equal importance (that's why I went with foam). It makes a huge difference in comfort.

Secondly, there is a large volume of helpful information on the web .... I would suggest starting at and DoE has some good publications too.

As to moisture, if it is coming in from the outside then sealing might help.

Third, if you examine your attic more closely, you may find that your wall system is open at the top. That is, there is no cap for the space between the back of the plaster and the inside face of the block. With air drawn in around hvac registers, electric outlets, and your baseboard, the walls are acting as chimneys. If you have good access from the attic, you can seal the top of this space with foam in a can. You may even be able to inject foam into the whole wall system. There are some R7 per inch foams that can be DIY installed, but they are expensive. To my mind, there are also issues with filling the cavity and possibly over filling it (the foam expands) and cracking the plaster. Your mileage may vary, esp. since I haven't tried them.

Fourth, you will probably find plenty of other openings from the conditioned space into the attic. I was amazed when I removed my insulation -- the interior of some walls was open at the top, and the top plates of other walls were poorly sealed. If air is escaping, you will see the underside the insulation discolored by dirt. Yes, there is a reason why fiberglass is used for furnace filters -- which should tell you that it does NOT stop the flow of your nice warm air. Cover these openings with plastic or caulk, depending on their width. You can fill a plastic bag with a hunk of fiberglass insulation and stuff it into a hole as well.

Finally, if you do insulate the block itself, the behavior is a bit unusual. It is still thermally massive, so it tends to keep the house cooler after a cold spell and warmer when the temp drops. I'm still trying to figure it all out.
Old 02-10-05, 09:46 PM
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JTDOUGLAS--who did you use for the core-fill 500?

I am also in Northern Virginia, and I need to have the same job done to my 1950's cinder/concrete block home. It doesn't have any insulation, and we need it this winter! Can you tell me what contractor you used? I'm shopping around, and need recs. Thanks!
Old 02-11-05, 07:37 AM
Pat S
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Many issues

You have too many issues for me to address here, but I will tell you to leave the asbestos tile alone unless you want a huge headache. It is difficult to dispose of and removal should (and may be required by code to) be done by professionals. Best bet is to cover with vapor barrier and rigid insulation and then new floor covering (see below). You may not need to add heat (radiant) to floors (I know concrete is unforgivingly cold!) after upgrading floor and other insulation and imoisture, infiltration barriers in the house, as your new HVAC will now probably be oversized (you did it backwards - upgrade house insulation, etc, then upgrade HVAC). I would focus on sealing the envelope (moisture barrier)on outside before doing anything, as the moisture problem will eventually ruin any other work you will do.

Flooring - Relatively basic solution is to (if concrete is dry) Hilti pressure treated sleepers to concrete (leave tile there) - sleepers spaced out and thickness depending on rigid insulation thickness. Insert rigid between sleepers, cover whole floor with 6 mil plastic sheeting, screw 5/8 or 3/4 tongue and groove ply - then cover with your choice of flooring. Use heavy duty adhesives under sleepers and T &G to prevent squeaks. Laminates, cork or carpet with a good backer are good choices and will help isolate the cold from your feet - and entire system will be much more comfortable as far as "give" (ever stand on concrete all day?). Proper prep work is key to good installation.
Old 02-13-05, 04:43 PM
Join Date: Jan 2005
Location: Northeast Florida
Posts: 213
What about styrofoam insulation? Has anyone ever used this? It is very thin, so you could install this in between your furring strips on your walls. Im not sure what the R- rating is, and dont know how costly this would be, But it may be an option? RH

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