Advice For Insulating an Outside Concrete Wall

[Todd]

I have a walkout basement where one side is an exposed concrete wall. I would like to insulate this wall and was wondering if anyone has any ideas. Is there any kind of product out there like 1/2" insulated siding board, or am I stuck with styro foam insulation and regular siding over that. I was told they don't sell the wood siding I have on the rest of the house, I think it's called T1-11, so I can't match it? Maybe there is some kind of insulating stucco? Thanks.

 

[steam man]

I used 2" styrofoam and then used a product similiar to stucco over that around my foundation. I painted it and it has been there 18 years. I can't remember the stuff I used but just score the styrofoam and plaster it on.

Mike

 

[peakbagger]

I will put my standard warning that carpenter ants love to tunnel thru this foam board even if its covered with stucco. It does not need to be damp for this to happen. It looks like you store wood in that area so I would urge you to find something other than standard foam. I have heard that there is a foam that is made with a borate additive that soves the problem, but havent seen an actual product yet.

 

[Todd]

Thanks for the reply guys. How do you put stucco over foam board? Just slap it on, or do you have to have mesh wire for it to stick? I thought I saw a home show on TV once using some kind of finished insulated board for this, but can't find anything on the net. The firewood was just put there temp to make room for building my wood shed.

 

[steam man]

I think one time I had some ants get through the foam board. Nothing a little chemical warfare couldn't handle. The garter snakes were another issue. I had to wait until I thought they were all out and use some expanding foam on the hole. I can't remember the name of the coating but it was basically just a fiber reinforced stucco. 5 gallon buckets. Got it at my local building supply store. I roughed up the foam board with the tooth side of the trowel and just put it on. Lasted a long time. Needs a few touch ups due the weed wacker. I am thinking the ants don't get through the coating if you go below ground somewhat.

Mike

 

[mbcijim]

An option to consider is the spray foam inside the hopefully hollow core of the block. Do not use the little styrofoam beads (vermiculite), they only add an R-2 or R-3. Depending on the width of your block the spray foam will add R-8 to R-11 if memory serves me correct.

It's pretty easy to install, they drill a hole, and insert the spray foam. You'll probably prefer to do it from the inside. I've done it commercially on some buildings I own, it worked fairly well.

Another option (but probably significantly more expensive, is to add a stud wall with fiberglass insulation inside.

If you're concerned about building out the thickness of the wall and creating a ledge on top of the new insulation, below the T1-11, it's impossible. Insulation takes up space. You're T1-11 only comes out 3/4" or so. I'd recommend stopping at a local lumberyard (ABC, 84 Lumber, etc..), not Lowe's & Home Depot, show them your picture and ask for advice.

So if you don't want to build out your only choice is inside the block or inside the house.

 

[begreen]

I too am thinking interior insulation, though prolly with foam board or spray foam. The problem with adding insulation + cladding to the exterior is that it will be proud of the house siding. Think of water sheeting down the siding, then hitting this bump out of insulation and siding. It can be flashed I suppose, but it's not my first choice. I don't think it would look right either.

 

[Todd]

I already have interior insulation, but it's only 1" foam board. I thought about changing it to 2x4 studs and bat insulation, but it seems like a lot of work tearing it all out and replacing. I like the idea of the spray insulation inside the block, I'll have to look into that. Thanks.

 

[2.beans]

a friend of sprays a material similar to truck bedliners that he can add a flake to that can make it look like granite. you just spray right over the blue board. really strong, you can bounce rocks off it and dosent dent or chip.

 

[mbcijim]

I already have interior insulation, but it's only 1" foam board. I thought about changing it to 2x4 studs and bat insulation, but it seems like a lot of work tearing it all out and replacing. I like the idea of the spray insulation inside the block, I'll have to look into that. Thanks.

If you do it, ask for the chart that shows the added R-value. Don't take anyone's word for it. It's also not the cheapest option, but it is the least work and the least obstrusive.

 

[peakbagger]

Spray insulation inside the block is an expensive way to go and really doesnt give that great of an overall R value. Unfortunately the R value of the block ends and center ribs of the concrete is so low that even if you fill the center cavities with foam the overall R value for the wall is a lot less than putting a thin insulation layer.

 

[mbcijim]

Spray insulation inside the block is an expensive way to go and really doesnt give that great of an overall R value. Unfortunately the R value of the block ends and center ribs of the concrete is so low that even if you fill the center cavities with foam the overall R value for the wall is a lot less than putting a thin insulation layer.

We underinsulated a block building 3 years ago for code issues. I had to fix it. My choices were add studs & insulation (over existing studs & insulation) or insulate the core with the foam.

Foam was far cheaper, and I am pretty sure it achieved an R-11 on it's own. But that was for a 10" block. Their are charts available that will tell you the R-value. And since it is residential, I would suspect that he has 8" block. So I doubt he will achieve R-11.

You're right when you say that adding sheet insulation is cheaper and more effective. However, he doesn't seem to want to do that and was simply looking for options.

 

[4acrefarm]

how about foil insulation? It is available in solid, perferated, and bouble. It comes in 4' witdhs 250' long. Maybe side over that. I have used all three of these products and i love them. Google "foil insulation" and find products and information, they say it will relect 97 percent of heat. Good luck.

 

[Todd]

Well, I got a rough bid for $700 to spray foam into the block cavaties. Not too bad, but still thinking of options. What do you guys think of spray foam inside the block and then on the outside using Insuladd paint? I need to paint the house anyways. Or do you think this paint is just a scam?
www.insuladd.com

 

[Titus]

Insuladd and other ceramic additives are bullbleep. Waste of money, scam, snake oil, etc.

 

[mbcijim]

Don't know anything about the paint, sorry.

In concept, I don't see how paint can do anything besides extreme marginal improvement.

 

[4acrefarm]

I would use foil backed 2"foamboard, with stucko or fake brick-stone. You could put a "waterboard" on top, which is an angled thim piece to keep water out. When you insulate both sides of the block, the block becomes part of the sullutoin instead of the problem. Good luck.

 

[Rhone]

Hey Todd...

I would get http://www.styro.net/FoundationInsulationPanel.htm if possible, they even got installation videos.

To "attempt" to do it yourself you have to cover the wall with XPS foam & adhesive, then fasten it with tapcons & washers. Next, cover it with a wire lath(sometimes called wire lathe) (it will look something like below) and tapcon it in place w/washers

then cover it in stucco/cement which will shape & bond to the wire lath and be secure. It's a lot of tapcons, drilling, and washers and I don't recommend any of this, besides being a lot of work I did it, and it looks like *@#!. My basement is bumped out away from my house now (I added 2" and the stucco/cement is another 1/2" - 1") it looks funny and I found out it's not possible for noobs to spread stucco/cement evenly over the wire lath, bolts, etc. looks like a bunch of kids did it in my case and likely lowered the value of my house. Kind of wished I didn't do mine it looks horrible, or may still get the pros in to see if they can repair or do something with it.

Now, it certainly improved things my basement has no inside insulation and after I did it the temps are now 10-15F warmer and I no longer have a fear of pipes freezing... but at the same time wished I could go back in time and at least for the stucco/cementing got the pros to do it (or get the item in the first link, it's worth the extra$ in my opinion so you don't decrease the value of your house).

 

[Todd]

Hi Ronemas,
Long time no hear. That is exactly what I was looking for. I could go ahead and spray foam inside the block and install those panels on the outside. Thanks.

 

[begreen]

Well, I got a rough bid for $700 to spray foam into the block cavaties. Not too bad, but still thinking of options. What do you guys think of spray foam inside the block and then on the outside using Insuladd paint? I need to paint the house anyways. Or do you think this paint is just a scam?
www.insuladd.com

Thermal bridging will make this a waste of money. Heat transfer will occur through the block's solid sections. If there's already 1" foam board on the interior walls, why not just add another layer? That will by far be the least expensive and most attractive solution. Also, is the rim joist tightly caulked, sealed and insulated? Rhonemas's point about lowering the house value is a good point. Don't do something that will lower the house value.

 

[Todd]

Well, I got a rough bid for $700 to spray foam into the block cavaties. Not too bad, but still thinking of options. What do you guys think of spray foam inside the block and then on the outside using Insuladd paint? I need to paint the house anyways. Or do you think this paint is just a scam?
www.insuladd.com

Thermal bridging will make this a waste of money. Heat transfer will occur through the block's solid sections. If there's already 1" foam board on the interior walls, why not just add another layer? That will by far be the least expensive and most attractive solution. Also, is the rim joist tightly caulked, sealed and insulated? Rhonemas's point about lowering the house value is a good point. Don't do something that will lower the house value.

But won't it help if the outside wall is insulated as well? I went to Menards today and they have some paint/stucco stuff you can apply directly to foam board after roughing it up. If I went with the spray foam inside the block and installed 1/2" foam board and paint, it would be even with the house siding and help the R value. The inside is already finished off with 1" insulation and paneling and I don't want to tear it all down.

 

[begreen]

To figure out how much it will help will require an analysis of ROI * hassle factor. The real question is how quickly will you see that $700 for the foam in block return to your wallet in savings? Also keep in mind that the exterior solution will need more maintenance over time due to weathering.

No matter what you do it will be work and a hassle, so go for the best return on your dollar invested. Can the interior paneling be saved and recycled once additional insulation is added? If redoing the interior has a faster payback + lower maintenance, then that's the way I'd go.

 

[mbcijim]

I disagree with all the comments about thermal bridging. Nearly every exterior wall has thermal bridging. 2" x 4" with fiberglass batt, thermal bridging. If they are selling it as an R-8/11, they are looking at the whole wall, not just the best parts.

Masonry walls seem to be more about mass than bridging.

 

[peakbagger]

The thermal bridging issue is significant. If you want to get complex to calculate the impact, fire up a finite element analysis program, but a darn good approximation is to take a concrete block and a t square and measure up the amount of surface area of the block that is straight path from inside to the outside consisting of only concrete versus the amount of block that is a path that consists of a sandwich of concrete foam and concrete. Now calculate the heat transfer through the surfaces using the U value (1 divided by the R value) multiplied by the temperature difference between the inside and outside and you will see that areas of the concrete block that don't have insulation have such a significant heat loss that the foam doesn't really contribute that much to the overall heat transfer. Now add a layer of thin foam over the entire surface area and see how much that drops the overall heat transfer.

Where the complex math comes in is that the heat doesn't travel in a perpendicular path from inside to outside, as the U value of the block is so bad the heat will also travel at an angle to the block increasing the surface area for heat to conduct out to the air. If you look at it with a heat camera, you will see a warm band on the block that is much wider than the area that is a straight shot of concrete. This just makes the heat transfer out of the block worse, so ignore this effect for now.

A good foam contractor will know this, but he is in business and the customer is always right (even when he is wrong). The contractor makes most of his money on labor, not material so if the customer wants to him to spend a lot of time drilling holes in blocks, great, that a few more hours of billable time. Do note that filling the blocks with foam does reduce the amount of noise transmission, so at least there is some value in the procedure.

 

[precaud]

Hey Rhonemas,
Nice to hear from you again, I hope all is well.

Thermal bridging: bagger is right, no need to overthink this one. Heat WILL escape where insulation isn't, period. Isolating thermal masses requires a continuous barrier to be effective.

Interior vs exterior insulation: I have a 9' daylight basement, about 2' is above grade. Over the last couple years I've done a combination of interior and exterior insulation to it (see earlier threads for details.) While both have made a difference, it's sealed my preference for the exterior insulation. Getting the thermal mass inside the heating envelope makes for lower and slower temperature swings. And if you're heating with wood, that makes it a space that is easier to heat.

I'm becoming increasingly intrigued by the concept of "wing" insulation, insulating horizontally around the perimeter of the house, to reduce the temperature difference that the basement wall insulation has to deal with.