R-value of Brick, Wood, Fiberglass, and other Materials

Summary: Brick isn’t a good insulator as is commonly thought; other tips for saving energy.
Tags: insulation, brick, fiberglass, R-value, energy consumption


I want to insulate my brick house and was talking with a company which drills holes in from the outside and injects foam.

Any advice?

Also looking to insulate my 3rd floor. Not much attic space for insulation to be blown in, no access points etc. The roof line is the ceiling on the third floor. It is a great space but cold in the winter and the ceiling gets very hot in the summer. House is from 1915. Is there a good solution?



Brick is commonly thought to insulate well, but actually it’s pretty bad. It has other good qualities though — moisture permeability, thermal mass, and it doesn’t rot nor need painting, etc.

The basic R-value of 1 is basically equivalent to one inch of solid wood, so for solid wood the value is 1 R per inch. Brick is much less at 0.2 R per inch.

Roughly (R/inch):

.2 Brick
1 Wood
3 Fiberglass or cellulose
4 compressed fiberglass
5 Styrene
7 polyisocyanurate
?? vacuum panels boast much more but are still way too expensive

So, with
1 inch of polyisocyanurate you can get the same effect as
7 inches of solid wood, or
35 inches of solid brick.

Most probably they pump polyisocyanurate in the gap between courses of brick, and double or triple the final R value of the brick wall by doing so.

R value is NOT the only important value though. If you insulate such that you don’t allow the moisture out, you can end up with rot or water-logged (and less-insulating) insulation.

Thermal mass will reduce heating and cooling in the spring and fall when there are 55 to 80 degree days/nights, but has much less benefit in the Summer and Winter.

Depending upon your house, lowering the thermostat for a few hours during the day may or may not save energy because the catch-up is less efficient. It is my untest opinion that the very massive houses typical of OTE, don’t benefit from daily thermostat setbacks, and in fact, it is possible in some situations that it may burn more fuel than leaving it at a constant setting. On the other end of the spectrum, low thermal-mass houses with little insulation can benefit from daily themostat set-backs though.

To cut down your energy bill, reducing air infiltration should be the first step. You can add R-50 everywhere and not notice much of a savings if your house is ‘loose’. Very often people insulate when actually they should be caulking, fixing windows, and sealing holes in the foundation and the top floor ceilings. After you have made your house tight, then focus on insulating.

Direct-vent furnaces and water heaters also help in that they don’t need to pull outside air in through your house for combustion, they pull and exhaust air directly through a dedicated vent.

Wed, 03/14/2007 – 16:05 — registereduser (not verified)
vapor barrier

what’s the best way to deal with a vapor barrier? Is primer a vapor barrier? What about Tyvek?
Wed, 03/14/2007 – 16:34 — Quint
Some primers are vapor

Some primers are vapor barriers, some are not, you have to check the individual products.

Generally, the best place for a vapor barrier is on the interior wall surface, i.e. the interior paint. Shellac, like BIN, is a good vapor barrier. Any moisture inside, will stop at the shellac and not travel outward and get your insulation wet, or cause rot. Regular interior wall paint is usually not a vapor barrier — the moisture goes through it.

If you are in an air conditioned home in a hot humid region, you will need the vapor barrier to be on the outside instead. Basically, you want to block the water vapor at the first surface. For most homes, the vapor inside, moving out, is usually the problem.

Tyvek is a plastic sheet that stops liquid water, but allows water vapor through. It is to prevent water from spashing, spraying, or blowing in. Is it similar to Gore-Tex but has a slower transmission rate. From a research project I did ten years ago, these are the numbers I recall. Tyvek breathes at about 35 milliliters per square yard per day. Gore-Tex breathes at 3000 milliliters per square yard per day. There were several types of tests for breathability too, so take this only as an illustration, not as hard data.


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