ANYONE WHO lives in an older row-house had to shudder at the collapse of a wall recently in Baltimore that left seven people injured.
Alas, such a collapse is not a freak accident -- the wonder is it doesn't happen more often. The problem is that row-houses are connected; from the outside walls of the end units all the way through, the row is one structure. Each unit gets its stability from being part of the row, from being one layer in a rigid horizontal sandwich.
Some row-houses, especially the older ones, are separated by a party wall only a single brick thick -- that's just 4 inches. Only on the ends of the end units and on the fronts and backs of each house are the walls two bricks thick (a mere 8 inches). So tearing down one unit in the middle of the row can be problematic.
Houses that get into the worst condition tend to be unoccupied ones that have lost their roof or somehow started allowing large amounts of rain water into the structure. Eventually the water weakens the structure, and the walls and floors collapse.
In the Baltimore case, a work crew had previously demolished an unoccupied rowhouse and had come back to shore up walls of the occupied houses on either side of the gap. A backhoe was working in a trench when the wall of one house collapsed across the gap into the wall of the other house, pancaking the top two floors. Six people in one house and the backhoe operator were injured, though none seriously.
Despite the problems, old brick rowhouses are not inherently dangerous. Virtually all structural problems can be solved. Even if the masonry wall is so unstable it is moving, it can be repaired and the walls made safe.
Anyone with a wall problem should hire a qualified structural engineer to write a specification that will solve the problem.
To get a handle on the kinds of things that can go wrong and how to resolve them, we talked to Tim Sibol, an engineer with Skarda & Associates Inc. of Baltimore. Here are some of the common problems he has seen and the solutions:
Problem: Bowing front or rear walls. Most rowhouses are built with the joists running parallel to the front and rear walls of the house. The joists are pocketed into the side walls or party walls. So the front and rear walls are connected only to the side walls.
According to Sibol, the roof weight is loaded onto the top of the front and rear walls. The roof weight pushing down on these walls can cause them to bow outward. (They can't bow in, because the joists will stop them.)
Solution: Bows can be corrected by connecting the front or rear wall back into the joists at each level. Engineers can determine how much force is being applied to the wall and what technique should be used to stop the bowing.
Problem: Footings under masonry walls are not reinforced concrete. Sibol has seen masonry walls constructed directly on top of a layer of stone laid in the bottom of a hundred-year-old excavation. Another typical old footing is a stepped-out brick footing at the base of the excavation with the masonry wall laid on the top "step." These footings are fine if they're left untouched. However, if you need to dig below the level of the bottom of the wall, such as to install a furnace, reroute stairs or to increase ceiling height of the basement, you need to do something to stabilize them.
Solution: Underpin the walls. You should never dig below the level of the bottom of the wall (even if you are leaving the footing untouched), without consulting an engineer to determine how to underpin with a new concrete footing.
Problem: Party walls do not extend all the way to the roof. There are rowhouses in Baltimore where the masonry party walls stop at the second or third floor ceiling; the attics actually are open to one another.
Solution: You can provide fire protection at the ceiling on the top floor by adding two layers of one-hour rated, fire-rated drywall or extend a fire-rated wall to the roof.
Problem: No support at the bottom of the basement walls. Instead, the floor may be dirt or cracked concrete. If the basement floor is at the same level as the bottom of the wall, there may be nothing to keep the basement wall from pushing in and bowing the wall above.
Solution: Consult an engineer about bracing or buttressing the wall.
Problem: Third-floor rear walls in old rowhouses often are masonry supported only by an old wood beam at the level below. Over a hundred-year period, water may get in and cause the beam to rot. The weight of all the brick may start to head down toward the basement.
Solution: Some people replace these walls with wood-frame walls to save weight. However, you must be careful to make sure that the side masonry walls are still tied in through the wood framing so the house forms a solid structure.
*original article written June 29, 1997|By Karol V. Menzie & Randy Johnson*
Boyd Construction Co
Family owned and operated in the greater Washington DC area since 1932.