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Question DetailsAsked on 1/4/2018

Is it possible to supplement our R11 insulation with spray insulation?

Our newly purchased house is freezing! We are thinking of improving our insulation and installing a fireplace insert to supplement our electric forced air heating system. One contractor quoted us ~ $7,000 to spray insulation into walls to supplement our R11 insulation, claiming it would result in less lost heat and more efficiency of our heating system. Another contractor said this isn't even possible, claiming that the existing R11 in the walls would simply get in the way and prevent spray insulation from getting into the wall and dispersing evenly.

So, is it even possible to supplement R11, or would it indeed get all smooshed?

Thanks for your help, everyone!

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1 Answer


OK - I would give the first guy a very negative Review. Spraying foam insulation into already insulated walls is a lost cause - useful only if you are trying to fill voids at the top of the stud bays due to settlement of unstapled batting or badly settled loose insulation.

I would say what you need to do is figure WHERE your $ are best spent - and for that you need a certified Energy Efficiency Auditor (or through an Architect if looking at doing a general remodel). The audit will show where your energy loses are and should provide info on where your $ will be best spent - may be attic insulation, crawlspace/unheated basement insulation of the overlyuing floor, wall insulation, windows, air leaks, etc. It is common for your unit cost per unit of energy to vary by a factor of 10 or more between the various alternatives.

The energy auditor can also (for added cost) perform an evaluation, based on nameplate ratings, of your heating furnace/boiler to determine whether it is even adequately sized for your house size - as is, and after estimated improvements. Sometimes the basic heating system is the problem - a lot of new tract homes are pretty marginally sized. For instance, in our area, most homes over about 15 years old run about 80,000-120,000 Btu for about 1800-2000SF home with "normal" insulation - yet a lot of the new construction with little better insulation sometimes are coming with 50,000-60,000 Btu units which end up running almost continuously even in above zero temps - when our design low temp for heating systems is about -30F. I have seen new construction which cannot hold 50 degrees, with the furnace running continuyously (which is a dangerous thing for it to do) in low ambient temps over several days.

Be sure to also get (from auditor or online) information on any local utility or state or federal energy credits available - for weatherproofing, insulation, or upgraded heating system. In some cases, a very large percentage of the cost may be recoverable by credits - either direct-paid ones by utilities or state/local energy or housing authorities, or tax credits.

Short of tearing out drywall (at least a strip across the bottom) to enable removal the existing insulation and then foaming the stud bays in-place (and even that makes a mess of electrical boxes and such), improving your wall insulation is pretty much a lost cause unless you are doing a very major remodel or residing job where the stud bays will be exposed anyway on one side in the course of the work.

If looking at redoing siding anyway, then reinsulating - either in-wall insulation (though that is only likely to gain you about 10-30% in R-value with open cell foam, maybe as much as 50-80% gain with the much more expensive closed cell foam, but at a pretty steep cost relative to the R-value gained in either case. Normally improving wall heat loss/gain characteristics relies on exterior foam board insulation on the outside of the studs when redoing siding - though if windows are not being redone at the same time the windows can be a problem because thery end up recessed because of the added thickness.

If the windows are very energy ineffecient (especially if single-pane now) sometimes just replacing them can make a significant difference - though at much higher cost per unit of energy savings.

Commonly, your best value per $ is in sealing airloss points (weatherstripping, foam insulation around doors and windows), heat-retaining curtains on windows (insulated curtains made a dramatic difference on our cold-area home), and sealing off air passages into the attic and upgrading attic insulation to an appropriate number for your area (commonly around R-24 to R-30, up to R-60 in some very cold or hot sunny climates).

Answered 2 years ago by LCD

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