Q&A / 

How to Insulate an Older Brick Home

DEAR TIM: My story-and-a-half brick home was built in the 1960's. It has no insulation in the walls as far as I can tell. Each contractor I have talked with wants to drill holes in my interior plaster walls and add insulation from the inside. I prefer to have it done from the outside by drilling holes in the mortar joints between the brick. I don't want all of the dust and repainting mess inside my home. How would you approach this job? What are my alternatives? Bill B., Versailles, KY

DEAR BILL: The house you describe sounds exactly like that of my in-laws. My wife grew up in a brick home built in the 1950's just before your home was constructed. The exterior of the home is used brick and the second-story dormers that project through the roof out the back of the house are wood frame. The exterior walls of the first story are solid masonry, not brick veneer which is the way most brick homes are now constructed.

Today's modern brick homes have a single-thickness of brick that is placed over a wood-framed structure. The wood walls can be covered with insulated sheathing and the wood-wall cavities can be filled with insulation. Solid-masonry walls can be insulated with modern foam panels that separate the outer layer of masonry from the inner layer, but this method of construction was not in widespread use when your home was built.

The majority of solid masonry brick homes that were built in the 1950's and 1960's were constructed at a time when energy costs were very low. The masons who built the structures used a finish brick for the outside facing that was usually about four inches in depth. The inner layer of the masonry wall was often concrete block or cinder block that was also a little under four inches in depth. These block were laid immediately behind the exterior brick. If you can determine that your masonry walls are about eight-inches thick, you know there is no foam insulation between the brick and the hidden block.

Drill a two-inch hole in a closet wall to see how much space you have for insulation. PHOTO CREDIT: Tim Carter

Drill a two-inch hole in a closet wall to see how much space you have for insulation. PHOTO CREDIT: Tim Carter

After the masonry work was completed, carpenters would follow behind and nail 3/4-inch thick by perhaps two-inches wide furring strips to the masonry walls. These wood strips were usually placed 16-inches on center and fastened to the masonry walls with hardened, cut nails. Large sheets of gypsum-based plaster lath were then nailed to the furring strips and the final plaster was applied over the lath boards.

If your home is constructed in this manner, you can see the problem you have. The only void space that is available for insulating is the narrow 3/4-inch space between the furring strips. You can confirm this narrow void space exists by creating a two-inch diameter hole in several of your exterior walls. Do it behind a piece of furniture or inside a closet that is on an exterior wall.

If you discover you only have a 3/4-inch space between the back of the plaster or drywall and the beginning of the block facing, you might never get a payback in energy savings in your lifetime for the amount the total job would cost including all cleanup, replastering and repainting. I say this even if you could insulate this space with the best foam insulation currently available.

The contractors you spoke to are correct. Attempting to do the job from the exterior presents a host of problems. For one, the mortar joints are often no wider than one-half inch. A tiny insulation tool would have to be inserted in eight inches and then somehow have to turn a sharp 90-degree angle to squirt insulation up, down and sideways. A specialized nozzle may indeed exist, but then you have to wonder if the entire cavity is being filled with insulation.

What's more, the furring strips present a challenge. They can't be seen from the outside of your home and a hole drilled into the brick at a furring strip location would be useless. Drilling larger holes inside the home allows the contractors to see if they missed a furring strip and it allows them to more easily install the insulation.

But if it were me, I would not even try to insulate the walls. I feel you can save more energy concentrating your efforts on stopping air infiltration leaks, installing the best energy-efficient windows and exterior doors and improving insulation in your attic space.

Calculating energy savings for insulating the narrow 3/4-inch wall space is fairly easy. Heating and cooling contractors have done this for years. They have to perform heat loss and heat gain calculations that allow them to properly size furnaces, boilers and air conditioners. Businesses that sell this equipment to contractors often have sophisticated computer programs that can quickly tell you how many Btus (British thermal units) of extra energy are required to heat or cool a home that does not have insulation in that narrow void space. I have seen the calculation differences and they are indeed very small.

But when you start improving the performance of windows by installing ones that have high-performance Low-E coatings, an overall R-value perhaps 500 percent higher than original windows and a shockingly low air infiltration rate, you start to make serious energy-savings headway. Adding reflective-foil-radiant barriers in attics, in addition to upgraded insulation, can also help save energy dollars.

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4 Responses to How to Insulate an Older Brick Home

  1. IN REGARDS TO THE TYPE OF CONSTRUCTION YOU REFERRED TO ABOVE. IN MY BASEMENT BAND THERE SEEMS TO BE AN AIR GAP THAT RUNS UP BEHIND THE PLASTER. IS THIS PART OF THE DESIGN? CAN I SEAL THIS OFF OR SHOULD I LEAVE IT OPEN?

  2. I own a 1909 stone home. The interior walls are plastered. I know the walls are not insulated, and I have done some homework about blown in insulation, but I also worry about a moisture problem after the insulation is in the walls. I have read that this may cause mold to grow due to the lack of a moisture barrier on the exterior wall. What is your opinion and is there any other way to resolve this dilemma?

    Thank you,
    Brenda

  3. Breeze way was built between house and garage out of wood front and back and the walls are insulated. Like to insulate garage side, which is inside garage and out of the weather. It is not a heated space but dry. My plan is to put foam board against brick and sheetrock the wall. I do have some heat in breezeway for our dogs when they are home alone. Brick wall is about 8 inches thick. The house itself has vermiculite between brick and plaster, I have new windows so I have seen it, is this ok?

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