Rebuilding Rowhomes Right: The Science of Making Baltimore Rowhomes Healthy Homes
Baltimore rowhomes are iconic. More than any other city, Baltimore is defined by its rowhomes. From the architecturally stunning homes of Bolton Hill to the modest alley homes of Fells Point, rowhomes have been providing shelter for over 100 years.
The housing stock is showing its age, leading to a boom in renovations. Many old houses have been restored and finished beautifully, but oftentimes contractors treat rowhomes like wood-framed suburban houses. If you are planning to remodel a rowhome, it is important to consider what building science tells us about modernizing historic masonry structures.
How Rowhomes Were Built
When planning a rowhome update, you first need to understand how they were built and how they functioned. Most rowhomes are built with double-wythe brick walls. A wythe is a single layer of vertical brick. The two wythes are tied together to provide support to each other.
Exterior bricks were fired at a higher temperature and are more resistent to water. However, the softer interior bricks—often called "salmon brick"—are much more susceptible to damage from wetting.
Floors and roofs were framed with wood joists that span the width of the house. These joists were pocketed into the brick party walls. Rowhouses were designed with "flat" roofs, though they are more accurately described as low-slope roofs. They are pitched slightly to shed water to the rear. Due to this design, there is no attic space like a suburban gable roof would have; instead, you have a "compact roof" cavity.
The fact that so many homes have survived over a century is a testament to the durability of the construction. You may think that durability means your rowhome will not be affected by your remodel. You would be wrong.
How Common Remodels Fall Short
When these homes were built, insulation wasn't a priority. Large fireplaces and coal-burning boilers provide cheap heat. As anyone who has received a recent BGE bill can tell you, we no longer live in a world of cheap heat.
The most common way contractors address insulation is by stuffed fiberglass batts into the walls and ceilings. While fiberglass slows the transfer of heat, it does not prevent air movement.
Moisture moves from warm to cold and wet to dry. When warm, moist air from the house reaches the cold brick wall or roof sheathing, you get condensation. The first surface that moist air comes into contact with that is below the dew point is the "first condensing surface". Brick will suck up water like a sponge, and wood that is unable to dry will mold and rot. To prevent this, code calls for a vapor retarder. Some builders us "poly"—a thick plastic vapor barrier—to prevent moisture from entering the wall. But by using a total vapor barrier, the wall cannot dry to the interior. While that may work in some climates, it is a disaster for Baltimore brick due to solar-driven moisture.
When it rains, the brick absorbs moisture. When the sun comes out, it bakes the brick and drives that moisture through the wall into your home. If you have a plastic vapor barrier, that moisture remains trapped in your wall. This isn't just a structural problem; it's a health problem. Damp walls are a breeding ground for mold and dust mites. By controlling the vapor, we're controlling your indoor air quality.
The Lid: Why Rowhome Roofs are Different
If the walls are the lungs of the house, the roof is the scalp. In a rowhome's compact roof, you only have about 8 to 12 inches of space between your finished ceiling and the structural roof deck. Adding insulation to this tight cavity changes the physics of the house.
The biggest mistake we see if the "Vapor Sandwich". On the outside, you have a rubber membrane (EPDM or TPO) which is a total vapor barrier. If a contractor installs a plastic vapor barrier on the inside, they have effectively sealed the wooden roof joists in a plastic bag. Any moisture that finds its way into that cavity has nowhere to go.
Building Smarter
Smart vapor retarders can block moist air from your house from getting behind your wall but allow moisture already in your wall to dry to the inside. Examples include Pro Clima Intello, Siga Majrex, and Benjamin Obdyke VaporWise.
Since the majority of water is carried in the air, proper sealing of the membrane is a critical detail. Proper air sealing isn't about the roll of material; it's about sealing every penetration. Tying membranes to old brick walls or around joists pocketed in brick is difficult and requires a detailed, specialized team.
At Romano Carpentry, we specialize in these high-performance details—from smart vapor control to meticulous airtightness—ensuring your renovation is as durable as it is beautiful.
Contact us today to start planning a renovation that makes your home healthier, more comfortable, and built to last another century.
About the Author
Building a healthy home starts with the right plan. I'm Nick Romano, and I specialize in applying modern building science to the unique challenges of Baltimore's historic masonry. I'd love to hear about your vision for your rowhome. Contact me today to discuss how we can rebuild your home the right way.
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