Comcheck using 12" cmu with insulated cores. What to assign R-value

[Fast_Edd1e]

Im having some trouble trying to understand how to fill out my walls on comcheck in regards to a partially insulated cmu wall.

Contractor wants to use 12" cmu bearing wall and insulate the cores. No interior insulation Just 12": split face cmu. I have done this in the past for a car service bay, but prior to having to do comchecks.

So on the comcheck I select "concrete block, 12" partially grouted, cells insulated". But then it wants an R-value. Structural engineer says we will likely be grouting solid 32" o.c. vertically. Does comcheck have a place for that? Do i need to design a wall that a percentage is solid grouted and the rest is hollow with insulation? Does it know what percentage is being grouted? I wouldn't consider core insulation to be "continuous".

 

[Yankee Chronicler]

Im having some trouble trying to understand how to fill out my walls on comcheck in regards to a partially insulated cmu wall.

Contractor wants to use 12" cmu bearing wall and insulate the cores. No interior insulation Just 12": split face cmu. I have done this in the past for a car service bay, but prior to having to do comchecks.

What stage is the project at? Is the contractor the client? Have construction documents showing some other type of exterior wall construction been approved and permitted? Did you previously submit a COMcheck for some other exterior wall system?

I ask because IF this is a change to approved and permitted construction documents, the contractor in proposing the change bears ALL responsibility (and cost) for documenting that the proposed substitution complies with applicable codes and regulations, as well as bearing the cost of preparing and submitting amended construction documents to the AHJ.

 

[Joe.B]

If this is in the design phase, consider proposing ICF instead of CMU?

Advantages of block construction with better insulation and better strength. They're even some companies getting away from the classic Styrofoam:

Soundproof & Energy-Efficient Insulated Concrete Forms | Nexcem

Nexcem high-performance insulated concrete forms are a simple way to build. Each interlocking unit is fireproof, soundproof, and insulated.

nexcembuild.com

 

[Fast_Edd1e]

What stage is the project at? Is the contractor the client? Have construction documents showing some other type of exterior wall construction been approved and permitted? Did you previously submit a COMcheck for some other exterior wall system?

I ask because IF this is a change to approved and permitted construction documents, the contractor in proposing the change bears ALL responsibility (and cost) for documenting that the proposed substitution complies with applicable codes and regulations, as well as bearing the cost of preparing and submitting amended construction documents to the AHJ.

This is still in the design phase. Exterior finishes are approved by the township. But pricing is being a large driver for decisions.

Ive done alot of research on the insulative values of cmu based on insulation type and reinforcing required and I am not finding a way of getting the wall to work in comcheck without some form of continuous insulation. Im reaching U-values of .232 for the wall system as single wyth. And im not interested in fudging the numbers when im getting envelope fails of -4%. So i think im getting it figured out and what is being proposed just wont work.

 

[Yankee Chronicler]

Have you reached out to the NCMA for advice?

I'm inclined to agree with you. The entire concept of dropping some bits of foam into some of the cells in a CMU wall never made much sense to me. It's better than nothing ... but not much better.

 

[jar546]

The entire concept of dropping some bits of foam into some of the cells in a CMU wall never made much sense to me

Nor I. Way, way, way too much thermal bridging and a lot of cells will be grouted anyway. To me, this is simply not an option.

 

[wwhitney]

There are some 12" insulated CMU products that claim R-values of 15-16. They are basically 3 wall products, a narrower (8"?) block with a facing of foam insulation covered by the third wall. E.g.:

Omni Block Seismic 12 Insulated Concrete Block - RCP Block & Brick

www.rcpblock.com

InsulTech

InsulTech thermally broken insulated concrete blocks create a high-performance masonry system that improves installation and thermal efficiency. Learn more.

www.echelonmasonry.com

But if you take a standard 12" CMU block and just add insulation to some of the cores, it won't perform as well. For a quick calculation, if a block is 8" x 16" on the face, and has (3) 1" thick webs, putting foam in the two cells could give you foam in 13/16 of the cross-sectional area. And let's say that 20% of the cells need to be grouted solid, so that's another 80% factor for how much foam you get. So you end up at 65% of the area having foam, 35% having just concrete. Then if concrete is R-0.1 per inch, the concrete portion is R-1.2. Say the foam portion is R-10. The overall U-value is 0.35/1.2 + 0.65/10 = 0.357, for an R-value of 2.8.

To first approximation, the heat loss is dominated by the concrete-only area, so the resulting R-value depends primarily on the percentage of the area that has foam in it.

Cheers, Wayne

 

[Mech]

We specify Cor-fill 500, which is a flowable insulation that gets pumped into the open cmu cells. The manufacturer has values for various cmu sizes and densities. https://www.core-fill500.com/codes.htm I contacted them years ago and they sent me info on 6", 8", 12" blocks for 60, 80, 100, 120, & 140 lbs/cu.ft. densities.

I make a composite wall R-value for COMCheck and HVAC calculations using a ratio of reinforced cells and insulated cores and their respective R values.

 

[jc_ks]

2018 IECC C402.2.2 -- Integral insulation in CMU walls cannot use the R-value method. You must use the U-factor method of Table C402.1.4. It's my understanding that the whole wall assembly would need to be tested in a lab for U-value for this to be acceptable.

 

[Henchalwoog]

I think you can use the "U value" option with trade offs?