Home>Discussions>INSULATION & HVAC>Plan for Do-It-Yourself foam injection between plaster wall & exterior brick – ?
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Plan for Do-It-Yourself foam injection between plaster wall & exterior brick – ?

My 1930s brick cape has new thermal windows, but I'm sure it's losing a lot of heat through the walls. I suspect there was never any insulation between walls and exterior brick – or else if there was, then it was quite ineffective and probably smashed down by settlement in the space between walls and brick. The walls and ceiling are constructed of an early precursor to drywall – I don't know what it was called but I'm sure some of you do. It is much thicker (5/8" at least) and much harder than modern drywall, and because of that material density probably transmits heat much more, even when it's tightly closing the air space between interior and exterior.

My goal is limited to improvement of just one room because it's a bedroom and is obviously the coldest room in the house. That room has several problems contributing to its coldness: On the north side of the house, has 2 windows, and has a closet backing up against 2 exterior brick walls. (The closet feels like a refrigerator when opened during cold weather.)

It seems clear to me that ripping out walls, installing spray insulation and rebuilding the walls would not make any sense financially. The entire living area of that floor is only about 600 sq. ft. and it's really not an expensive house to heat, overall. But I do need to improve that one room. I envision a low-budget, relatively uninvasive method of insulation and I am interested in getting some feedback.

The method involves a drill, numerous cans of spray foam such as "Great Stuff Big Gap Filler," and a "borescope" (similar to a pipecam and can be had for less than $30) attached to a laptop computer. From that description the general method would be obvious: Drill holes in the wall, spaced out over the entire wall area, and spray the foam in. The borescope rig, which has its own LED light source built in, would help solve the big problem of establishing what's behind the wall already and to observe what happens when you spray a good amount of foam in there – (Where does it fall to? How much does it expand?) – requiring only a series of patchable holes, probably around 1/2". I am thinking, from a few such observations made from nearby holes, one should be able to guesstimate how far apart these injection sites need to be and how much foam might be needed. I also figure that 100% fill would not be necessary in order to achieve a significant improvement. Afterwards, the holes would be filled and finished off. In comparison with any other method I have read about, it would be much cheaper and much less trouble to get the room back to normal.

If you have extensive knowledge of insulation issues, I will appreciate your comments on the proposed method.

Re: Plan for Do-It-Yourself foam injection between plaster wall & exterior brick – ?

Contractors that do spray foam in existing homes have formulas for amounts of foam to use and use foam designed for the correct amount/size of expansion within the walls. I believe the product used for existing structures is called homesulate, if I remember correctlly from a neighbor that remodeled recently.
Did you get a bid from one or more of these contractors before you figured out how much you think buying all of those cans of spray foam(which I imagine will be in the hundreds) will cost?
Also, that spray foam in a can is not designed to be used to fill voids like those found between your 2x4s.

Re: Plan for Do-It-Yourself foam injection between plaster wall & exterior brick – ?

In all likelihood you have brick bearing walls with rock lathe and plaster on the inside. There is probably little to no room for sprayed in insulation. Anyway your thought to use spray foam in a can will not work. It is not meant to be used that way and would cost a lot and probably cause a big mess and not fill what little if any cavity you have. If you want to try that route contact a reputable spray foam insulating company or three and see what they think after inspecting your house.
Another way to go would be to add rigid foam on the inside and cover with drywall. One and a half inches of polyiso foam would give you an additional R-11, polystyrene R-7 1/2. The 1 1/2" dimension works well with 2x lumber for furring and framing and doesn't take much out of the room. It would be a significant improvement. This modification could be DIY.
Don't forget about attic insulation. It should be R-38.

Re: Plan for Do-It-Yourself foam injection between plaster wall & exterior brick – ?

While I support DIY, and I do a bit of incidental insulating myself in my work, I have never found it possible to beat a Professional Insulator on larger projects so I just let my guy handle it. Even with the 'free labor' of DIY, the handling and clean-up gives them the edge. Plus I don't have to invest in any equipment this way- I imagine foam-spraying apparatus wouldn't pay off for one job. I'd get a few recommendations and quotes from local Insulation companies and let them have at it. It's not worth the hassle to me!


Re: Plan for Do-It-Yourself foam injection between plaster wall & exterior brick – ?

Thanks for all the suggestions. You convinced me not to try doing this myself.

Re: Plan for Do-It-Yourself foam injection between plaster wall & exterior brick – ?

The kind of foam that you need does not come in a can. You would need a slow expanding foam. The foams that come in a can expand quickly initially, get hard and then expand a little more, those would blow out your walls.

But now about the walls. If you have load bearing brick walls, which are more 18th century than 1930's, then the plaster would have been applied directly to the interior brick. There would be no wall cavity to insulate.

If you have a framed wall and a brick exterior siding, typical ofr the 20th century and today, then there is a gap between the exterior wall sheathing and the brick, you do NOT insulate this gap under any circumstances. That gap is necessary for moisture control. You will find some gaps between the bricks at the foundation level of the house that are not filled with mortar, those are weep holes and are necessary.

In this case, you can fill the wall cavity (between the studs that is) with a foam product or any blown in insulation. cellulose is commonly used for this as it is the most cost effective. There is a big advantage to ripping out the plaster (probably lath and plaster) though. You can upgrade any wiring, you can insure that there are no gaps in the insulation and you can use fiberglass batts if you want and add a vapor barrier. Then put up sheet rock.

You are correct in the plaster conducts more heat than sheetrock. It conducts heat about twice as fast, but sheet rock is not much insulation either. But that actually is a bigger factor than many people realize. About 15% of your wall is studs and those studs have about an R-5. So with typical R-13 fiberglass, only 85% of the wall is R-13, the other 15% is about R-5. This is where the conduction of sheetrock vs plaster comes in. Heat from inside the room strikes the plaster or sheetrock and if seeing an big barrier to heat flow on the other side (R-13) and low resistance to heat flow laterally (sheetrock R-0.2/inch, plaster R-0.1/inch) it will tend to travel along the wall surface toward the lower resistance of the studs (R-5) and exit the building.

A simple solution to this is to insulate the wall cavities with fiberglass batts or other choice of insulation without a vapor barrier, then cover the wall cavity with a 1/2 foam board, seal the edges with a foil tape and then a half inch sheetrock. This makes a thermal barrier that reduces the effects of the lateral transmission of heat. Of course if you do this, your wall outlet boxes and switches will have to be moves out.

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