My wife and I recently signed paperwork to build a new house with a production builder. We were picking out cabinets and stuff today we were asked if we wanted to fill the concrete block exterior walls with foam. I hadn't heard of this before and was curious what everyone's thoughts are on it if it's worth it or not. They said it would cost about $850 to fill the walls. The house we are building is 3854 sq ft 2 story in Florida. I know it's a massive house more than we were looking for but it was a good price in a good location. Thanks

IMO, you should broaden the question to what are all of the optimal levels for insulation, windows, air sealing, HVAC, etc.

Since this is a production builder we have no other options for windows,HVAC,insulation ect but we do have the option of foam filled block

Are these Concrete Masonry Units (CMUs')?

How exactly are they going to fill these walls and with what foam product (open or closed spray foam)?

I think the easy answer is, yes it's worth it. There is bound to be an energy savings given all the months that you will need a/c. $850 is a pretty low price for the benefit.

Posted By Lbear on 27 Jul 2013 05:30 PM
Are these Concrete Masonry Units (CMUs')?

How exactly are they going to fill these walls and with what foam product (open or closed spray foam)?

I do not know what a CMU is... I can't answer the info on the foam product right now.

Without knowing what type of materials you are building with one cannot answer the question properly.

Posted By tegguy on 27 Jul 2013 09:18 AM
My wife and I recently signed paperwork to build a new house with a production builder. We were picking out cabinets and stuff today we were asked if we wanted to fill the concrete block exterior walls with foam. I hadn't heard of this before and was curious what everyone's thoughts are on it if it's worth it or not. They said it would cost about $850 to fill the walls. The house we are building is 3854 sq ft 2 story in Florida. I know it's a massive house more than we were looking for but it was a good price in a good location. Thanks

Probably not. The thermal bypass through the webs of the block would render the foam useless. Spend the money on sheet foam on the outside or inside latter will give you more bang for your buck.

You might gain ~R3 in the wall. What the exact figure is and what it is worth takes more data and analysis.

> we have no other options

Might be worth asking if they would be open to having someone else do additional air sealing.

Posted By Lbear on 27 Jul 2013 10:19 PM
Without knowing what type of materials you are building with one cannot answer the question properly.

All I can tell you is it's a concrete block construction and I'd assume it's a spray in material done on site.

Posted By jonr on 28 Jul 2013 01:01 AM
You might gain ~R3 in the wall. What the exact figure is and what it is worth takes more data and analysis.

> we have no other options

Might be worth asking if they would be open to having someone else do additional air sealing.

They won't I've already asked about other stuff and they will only allow the people they use to do the work.

Posted By FBBP on 27 Jul 2013 11:55 PM


Probably not. The thermal bypass through the webs of the block would render the foam useless. Spend the money on sheet foam on the outside or inside latter will give you more bang for your buck.

I don't know if you mean later or latter. If you mean later I'm not going to pay someone to re stucco the entire exterior of the house just to add foam to it. The inside does have insulation by code between the interior and block. The foam filled block is just another layer of insulation. Yes there are still thermal bypass's because of the webs but the surface area is far less than without the foam since you will not have the thermal transfer in the open air areas of the block.

If forced to guess at some figures, I think it will provide for a good return on investment.

It sounds like you are in hurricane area of Fl. building with CMU. Are they filling the cavities of the block with concrete for more strenght?

Posted By robinnc on 28 Jul 2013 07:20 PM
It sounds like you are in hurricane area of Fl. building with CMU. Are they filling the cavities of the block with concrete for more strenght?

We are in a hurricane area but they aren't filling them with concrete it's some foam I'm trying to find out exactly what material

I do not know where you plan to build in Florida, but in high wind areas such as Citrus Hills, the builder uses concrete block (CMU) with a cementitious coating (not stucco).  At corners and about every 6', vertical rebar is grouted in the cores of the block.  Vertical rebar is also grouted in cores to reinforce openings in the walls.  The remaining cores are filled with a very low R-value (low pressure) spray foam.  Foil reflective paper is installed on the CMU walls from inside the home.  Overall, low R-value.   I liked the subdivision but I wanted more R-value.

The foam used in CMU cores is usually a ~R5/inch multi-polymer non-expanding injection foam. (eg TriPolymer, Core-Fill 500) It tightens up the place a lot, but it's relatively vapor-open. As others have noted, the webs of the CMU and any horizontal bond-beams cut into the performance (a lot!), and it often won't be cost effective.

These products usually take 8" CMU wall performance from < R2 to about R5-6 (Applegate claims R9-10, but I'd bet that's a clear-wall number: http://www.applegatefoam.com/Foam-Insulation-Products/C-Foam-Insulation.shtml) but an R5-R6 whole-wall performance is still a pretty crummy R-value even in southern-FL terms. But it probably brings it up to code-min as a mass-wall anywhere in FL:

http://energycode.pnl.gov/EnergyCodeReqs/?state=Florida

We are building in Winter Garden Florida. The foam is called Core Foam and is similar to Core Fill 500. The house has to meet min code without the fill otherwise they wouldn't be able to build it so this taking it above code.

Adding ~R3 to a code min wall in FL is a reasonable increase in R value, percentage wise. Take the percentage of heat loss through the walls, the expected annual heating/cooling cost and you can come up with an approximate annual savings. Compare that to the upfront cost.

Winter Garden FL is smack in the middle of US climate zone-2.  By some estimates the cost-effectiveness of wall-R (whole-wall) starts to fall off at about R15 (whole-wall, all thermal bridging accounted for.)   To hit IRC-2012 code-min without the injection foam using exterior EPS would only take an inch.

See: http://publicecodes.cyberregs.com/i...sec002.htm

But two or three inches of EPS (or 1.5-2" of polyiso) wouldn't be insane from a long term return perspective. See table 2, p10 of this document:

http://www.buildingscience.com/docu...mate-zones

The delta in labor cost of installing 1" foam vs. 3" is in the noise.  The cost-per-square-foot-per-R is on the order of 10 cents for either EPS or polyiso. (eg: R10 costs about a buck a square foot, R15 is about a buck-fifty/foot).  Without knowing what they're charging for the injection foam it's hard to say whether adding thickness to the exterior foam is cheaper or more expensive than the core-fill, but in my neighborhood it usually is.  If you made the CMU the drain-plane layer and used a sprayed on liquid weather resistant barrier (WRB) it would be pretty cheap, and would be at LEAST as air-tight as an injection foam treatment, and leaving the CMU cores open would be fine, provided the air-barrier at the ceiling level extends all the way out to the WRB.  Some foil-faced polyiso can be detialed as the WRB, and in new construction you'd have the option of installing the window & door flashing to the outer layer of foam to a back-vented rainscreen cavity behind the siding, which may be preferable.  If using EPS you'd need to add a separate weather resistant barrier (Typar, Tyvek, etc.)

With fiber cement siding, 2" of polyiso (or 3" of EPS), 8" CMU and 1/2" wallboard the whole-wall R would come in at about R14-R15 without the injection foam.

Whatever exterior-R you end up at, extending the attic insulation at full thickness all the way out over the top of the wall insulation is important, and may require a bit of spray foam to make continuous &  air-tight.