Michigan Code

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Moderator Post (s) for this thread: > Cinder Block home by Billhart on 01/30/2007 > CCinder block home by Billhart on 01/30/2007 > ATD by Billhart on 01/31/2007

Michigan Code, as in any jurisdiction that uses the International Residential Code and it's energy provision from Chapter 11 (based on the IECC-International Energy Conservation Code) views mass walls differently than it does wood framed walls.

But in order for a "mass wall" like concrete block to qualify for lower mass wall insulation levels, the mass walls must:

-Be covered on the exterior of the wall by at least 50% of the required insulation thickness or

-Have at least 50% of the required insulation thickness integral to the wall (ie. inside the open webs of the block)

Short of that, the wall must be insulated to the R-19 insulation thickness required of all wood framed walls.

And yes, a "Total UA Alternative" approach is allowed anywhere the IRC is adopted, whereby one takes into account all R-factors of every material in wall to come to a 'mass assembly' insulation requirement....But because of the nature of a mass wall like concrete block, one ends up with a WORSE UA alternative energy performance for block using this method and HIGHER required R wall R values than if one simply used the R values for a wood framed wall to begin with. In short, using a 'mass assembly' approach to this mass block wall only makes matters worse...
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The vapor retarder Billhart speaks of is code required under the IRC as are air infiltration methods for ALL WALLS. Nothing special here for foamed walls.

This vapor barrier and air infiltration control methods are even required by Code for FOAM insulated walls when foam is applied applied to stud cavities...so there remains NO ADVANTAGE using foam over fiberglass here. This is just standard practice under IRC no matter the insulation type.

The problem, again, with foams is:

-that they are expensive, and take scores of years to simply pay for themselves before one even begins to see a penny payback in energy dollars saved

-must have expensive thermal barriers applied over them to keep the foam from igniting in a fire furthering the payback time...

-foams can need even deeper thicknesses to achieve the same minimum R-values that even cellulose or fiberglass can provide. Condensed fiberglass can provide the same R-values as foam or better depending on the type of foam at a cheaper price.

As noted in my previous post, 4" of R-5 foam sheets would be required to meet the R-19 wall insulation in the original poster's house.....a thickness of 4" of foam, 3/4" of furring strips, and 1/2" thick drywall to thermally isolate the foam for a grand total thickness of 5 1/4" added to the walls...(and no one makes 5" or larger ramset nails to my knowledge).

And as previously mentioned, one can achieve the same insulation level using R-19 fiberglass in a 6" frammed wall assembly at far less cost and only losing 1" more total in room width and depth.

Using a COMBINATION 1" foam plus a full framed wall assembly with fiberglass is the more practical and cost effective approach, especially when the foam is placed on the EXTERIOR wall of the concrete.

So the correct answer is:

There IS no ONE 'correct answer'.

There are only many alternative paths to energy code compliance.

And one needs to decide for themselves which is the most cost effective and efficient for them.

As for me, and after building for many years, I have NEVER found foam alone nor any other insulation ALONE to be the answer any time anywhere.

Foam alone is too costly.
Cavity insulation alone does not solve all heat loss problems.

The "answer" is to use a combination of insulating materials and methods to achieve energy efficiency and economic affordability for any structure.

Foam should remain only a small portion of the total insulating package and be the LAST choice because of its lack of affordability.