Ask Your Question

Angie's List Answers is the trusted spot to ask home improvement and health questions and get answers from service companies, health providers and consumers. For ratings and reviews on companies in your area, search Angie's List.

Top 30 Days Experts
Rank Leader Points*
1 kstreett 240
2 Guest_9020487 110
3 Guest_9190926 105
4 GoldenKid 100
5 ahowell 95
6 KnowledgeBase 95
7 skbloom 80
8 Guest_98024861 70
9 Guest_9311297 70
10 Guest_9400529 70

*Updates every 4 hours

Browse Projects By Category

Question DetailsAsked on 10/20/2012

Is it a good or bad idea to insulate house walls if the exterior is brick and the interior is plaster?

It's been recommended that we insulate our walls. The house was built in the 1940s. The interior walls have some very fine cracks, not a lot but a few. We're concerned about what could happen if the plaster is drilled. And we're wondering just how much energy would be saved since we have a high efficiency gas furnace, energy star windows and doors, and R38 insulation in the attic.

Do you have the same question? Follow this Question

3 Answers


Yes, by all means, insulate the walls.  To avoid cracks in the plaster, have your painter patch the holes, not your insulator.  Remember, "The key to a good paint job is a good pre-job."

You have invested in ceiling insulation and an energy efficient furnace.  Furthermore, you've made a huge investment in high performance windows and doors but, the problem is you installed them into uninsulated walls.  

Remember another old saying, "The whole is greater than the sum of it's parts."  So, insulate the walls and you will be very glad you did.  Every house is different but, because you are finally completing the "thermal envelope" around your home, you may get as much benefit from the walls as you've gained with everything else you've done so far combined.  

Finally, there is one more important thing you should do.  Get a certified BPI Building Analyst to do a CAZ Zone combustion safety test if you have any combustion appliances in your home.

Enjoy the added savings and comfort!
Steve Anderson
Progressive Insulation & Windows
Chatsworth, CA

Answered 8 years ago by Steve Anderson


The single greatest energy loss in a home is either lack of attic insulation or loss of conditioned air. Your home is like a thermos bottle and air leakage out of the envelope can be huge . But a lathe an plaster home tends to be more air tight (than modern dry walled home) and most air leakage is straight up. So with your attic insulated #1, a high effiency hvac system #2, Air leakage # 3 ie gaps around the chimney , electrical lines running into the attic (old fashioned air sealing) Includes duct air leak loss, That is conditioned air leaking out of the delivery system prior to the room it terminates in a 4th. Window and sidewall insulation a tie for last. Remember you have to pay for the conservation measure before it gives you a return. For one additonal nifty way to save on A/C see my blog on radiant barriers.
Jim Casper Old Energy Conservation Guru
ps You don't believe me go to Oak Ridge National Testing Lab
pps you can run 1/4" drywall over the lathe and elinimate the cracking and any holes you had drilled to blow cellulose insulation (the best for the $)


Answered 8 years ago by jccasper


Blown in insulation is one of the worst things you can do in brick faced houses - in fact, I was just reading an article on the thermodynamics of that very subject earlier today for a historic house rehabilitation design. Here is a more simplified article that discusses some of the problems with insulating brick houses -

The problem with brick houses, excluding modern ones with a positive vapor barrier and ventilation gap behind the brick, is they absorb moisture, then release it to the wall cavity. Putting anything organic in there is inviting mold and rot in short order. In addition, insulating the cavity reduces the amount of heat escaping the house, hence there is less drying on the backside of the bricks, which increases freeze-thaw damage on the bricks, and increases rot/corrosion for any beams or headers or such that are in the wall or supported on the wall.

IF properly done, closed-cell anti-fungal treated foam-in-place insulation can be used AFTER providing the correct interior ventilation provisions. This in another one of the cases where more is not necessarily better - full wall cavity insulation can cause significant damage to the bricks, leading to total breakdown, and inthe case of solid load-bearing brick walls, total wall collapse. There have been several buildigns in New York and Massachusetts with substantial wall failure attributed to insulation resulting in brick failure or supported beam or header failure.

The thermodynamics and hygrometrics (heat and moisture factors) are much too complicated to get into here - you can google the phrase - insulating brick walls - for articles on the issue - concentrate on the professional ones from architects and building associations and the foam insualtion manufacturers, because there are some out there who recommend cellulose, shredded newspaper, and so forth behind brick, which is a big no-no. Ditto for stone, by the way.

I hate to say it, but the current recommendation is to use exterior insulation like EIFS or board insulation under stucco or gunite or a metal facade, not interior wall insulation - which destroys the brick appearance of course.

Suffice it to say, before going ahead with this, consult an architect certified in building insulation systems to assess your situation and make recommendations.

Answered 6 years ago by LCD

Related Questions

Terms Of Use
Privacy Policy