Upgrading insulation in a home with batts in the wall

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Permalink Reply by Bud Poll on January 13, 2012 at 11:02am

There are foam companies that will add foam to existing batt insulation, but I'm a skeptic and would want some guarantees and lots of IR pictures.  Maybe even a few addresses where this has been done before so I can look with my own camera.

Improving 3.5 inch walls is difficult.  If the foam can be done and done right, maybe, but at $2 a sq ft a 1,500 sq ft ranch would be around $2,500, I would run some numbers to see if that works.

In the long run, I always look inside and outside to see if other work is in the near future.  If new siding will be needed soon, then adding rigid foam under the siding might combine to be a lot less expensive.  If inside renovations are planned, padding out a wall, electric, windows, yada, yada, may also be an option.

One of the problems with adding foam to an already insulated wall is that the increase is not all that much and the existing fiberglass actually gets in the way reducing the quality of the new install.  So you end up going from an 11 or 13 cavity to a 15 or 18 cavity.  It would be better if the fg wasn't already there.  Those numbers came from my back pocket area so take your own guess, but they illustrate that the improvement isn't all that great.  Adding a couple of inches of rigid over the outside with new siding also covers from foundation to top plate along with all of the thermal bridging.  Much more impressive results.

Bud

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Permalink Reply by Jerry Nelson on January 13, 2012 at 12:43pm

Thanks, kind of what i was thinking. Lets see what others think.

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Permalink Reply by Patrick Michaelyan on January 13, 2012 at 1:07pm

I'm going to back Bud on this one. Spraying in foam and hoping it will effectively fill in around the FG is essentially hopes and dreams kind of thinking.

In a case such as yours, the best bet is to tighten up where you can, add insulation to places like the rim\band joists (if exposed), and begin to plan for a more comprehensive project in the future (where wall insulation is combined with interior renovation and\or siding replacement). 

In my neck of the woods, most houses are faced with a brick veneer (with no insulation in the walls), so the only real way to approach this is to talk to them about making a mess in their houses and them becoming okay with this over time. By "this" I mean the mess that typically accomodates drilling into the sheetrock\plaster, installing cellulose or icynene, and then patching up the holes used to install the insulation. 

Patrick

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