Look Behind the Brick
Brick has consistently ranked as a high-value type of home siding. There are several reasons for this: (Building Blocks: The Pros and Cons of a Brick House)
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Brick is durable and has less upkeep costs. If left in its natural color, it doesn’t need to be repainted; it only needs power-washing every once in a while to look new again. It won’t rot.
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Brick is less expensive to insure, due to its durability.
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Brick can be a better sound buffer than other sidings.
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Brick can be energy-efficient when combined with the right type of insulation. The thermal mass of the bricks cause them to be “reservoirs” of energy that cause the interior to heat and cool slowly.
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Bricks are more fire-resistant than most other materials.
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Bricks are eco-friendly, made from natural products like clay and shale.
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Bricks are naturally resistant to mold, rot, and mildew because they can cope with high humidity.
The average homeowner may not know that there are solid brick homes, but also more commonly nowadays, brick veneer or brick siding homes. In solid brick homes, the brick is the exterior walls, and what actually holds up the roof. It is several layers of brick in thickness, or an interior concrete block with a layer of brick on the outside. Solid brick is also referred to as “solid masonry construction” or “double brick.” In brick veneer, there is an interior wood frame to which is attached a single layer or (wythe) of brick. Most houses built in the last 30 years were constructed using brick veneer because of its affordability and ease of installation. (Solid Brick vs. Brick Veneer: A Look at Costs, Installation Processes and Benefits) Because brick veneer has an interior wood framing, it is susceptible to the problems that other sidings face: moisture intrusion, mold and termite damage. Veneer brick or brick siding can hide a lot of problems. Here is a picture of a cross-section of a brick veneer wall.
First of all, like concrete, brick is not waterproof. Brick is actually a moisture reservoir. Brick absorbs rainwater and holds it within its internal pore structure. Here is what happens after the rainstorm: When brick gets wet after a rainstorm and then is warmed by the sun, the water vapor within the brick is at a higher concentration than its surroundings. The water vapor within the brick is also at a warmer temperature than its surroundings. Some of the moisture will move out of the brick into the outside air because the outside air is colder than the brick and because the outside moisture concentration (absolute humidity) is lower than the moisture concentration in the brick. Unfortunately, some of the moisture in the brick will move out of the backside of the brick into the exterior wall cavity through the exterior sheathing. This happens because the brick is also warmer than the wall cavity and because the moisture concentration in the brick is higher than the moisture concentration within the wall cavity. (RR-0104: Solar Driven Moisture in Brick Veneer)
For a visual and more explanation on how water can damage the interior of a brick or stone wall, check out this video by expert builder Matt Risinger. At min 6:10 and after, Matt did a test to show how quickly water will infiltrate to the back of a stone wall. It’s within 1 minutes of sprinkling a water hose on the stone siding!
There are brick homes that have survived for decades without any moisture or mold problems, and some newer brick homes are experiencing mold in the interior cavities of walls or rot in the bottom plate of the walls. Why? There are two new-”er” developments in building walls (since the 1990’s): interior polyethylene sheet vapor barriers, and vapor permeable exterior sheathings and housewraps. Interior polyethylene vapor barriers prevent wall assemblies from being able to dry towards the interior during the summer months. And the trend towards more vapor permeable sheathings makes it easier for water vapor to enter walls from the exterior.
The mold and decay problems only occur where a permeable exterior sheathing called fiberboard has been installed. The problems do not occur where a foam sheathing, plywood or OSB has been installed. The reason for this is that the foam sheathing, plywood and OSB are less permeable than the fiberboard and therefore does not allow as much inward migration of water vapor diffusion from the brick veneer moisture reservoir.
Therefore, when buying a house or contracting for one to be built, you should become very intimately familiar with wall construction. If you’re buying a brick home, you should find an inspector that really knows construction in order to determine the type and order of wall materials, and whether there’s already been damage inside the wall from moisture and mold. Here are some telltale signs:
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Stains on/around the baseboard area
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Peeling paint (particularly in the lower part of the wall)
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Efflorescence (white powdery salt-like deposits), particularly in the lower part of the wall
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Musty odors
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A high reading with a moisture meter
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Foggy or dripping windows (moisture will vaporize at openings, and condense on cold surfaces like windows)
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Moisture damage of the floor near the wall.
The other problem with too much water in the walls is that it attracts termites and other insects. These insects are attracted to the moisture held in the wall.
Sealing “reservoir claddings” like stone and brick, according to Matt Risinger and other experts, is not a good idea, because water will still seep into the wall via capillary action: any small break in the sealant will still allow the water to be absorbed, but now the water cannot dry toward the outside; it is restricted and only can dry toward the inside.
Matt Risinger writes in detail about the design of the wall (that 1” air gap is needed), and the materials he uses so that the water absorbed by the brick/stone can dry from the outside and towards the inside. Towards the inside, he uses Tyvek Commerical Wrap for brick veneer with a 1” gap, and Keene Driwall over the Tyvek if stone is laid without the 1” gap. The Driwall holds the mortar off the Tyvek, allowing water to run down and out the bottom.
Exterior wall construction is just one aspect of a new home or home remodeling project–how many more details there are for a full house! If you’re interested in learning more about the “right” way to build–the way that minimizes the chances of moisture and mold ruining your home– check out the Building Science Fundamentals Courses offered by BSC, or just search their vast website here for free articles and videos. They are full of case studies of building gone wrong–so you can learn from others’ mistakes instead of your own!
