Problem Solved: Stopping Leaks After Heavy, Wind-Driven Rains

As part of our ongoing Problem Solved series, Habitat spoke with Douglas J. Lister, the principal at Douglas J. Lister, Architect.

Built to leak. I’d like to talk about two buildings. The first had serious leaks after several nor'easters and tropical storms. This building had a long history of leaks since it had been converted into a condominium in the 1980s. We started by inspecting apartments where we had complaints, and we found really, really moist, wet plaster inside the apartments. We found it throughout the building, even on low floors of this 17-story building. In my experience, typically on lower floors there really isn't a lot of damage, and that's because the upper floors receive the brunt of the damage during wind-driven rains. We estimated that we had water damage from about 50% of the exterior walls of the building, and that's a very high percentage.

I'm going to back up a little bit and explain that pre-war brick masonry buildings depend on the mortar that the brick is laid in to provide the waterproofing for the walls. We tested the mortar on this building, and we found out that it did not have much of the binders that we normally use in mortar, lime and cement. So it was very inexpensive. The building was built during the Depression, and the contractor had cut corners by using more sand and less cement and lime. We believe the building started having leaks right after it was first built. The solution was to remove the outer layer of brick and install a waterproof membrane system, then install new brick on top of it, what's called re-skinning. For this building the cost was about $4 million, a very big number.

An unconventional approach. The second building also had leaks after wind-driven rains. We again surveyed the building and found that about one-third of the apartments had leaks. We estimated that we were getting water damage from only about 10% of the exterior walls, so re-skinning wasn't warranted. We took an unconventional approach: we did the waterproofing from the interior rather than the exterior. It was an intrusive approach. We went into people's apartments and removed the plaster from the walls where we had had plaster damage. We put in a waterproof barrier on the exposed inside brick layer of the outside wall, and that barrier was a cement-based layer of basically stucco.

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Rather than replacing the plaster, we put in a moisture-resistant wallboard. It's been in place for several years, and it's held up very, very well through wind-driven rains. This was not an inexpensive solution. It came out to be about $10,000 per apartment, but I estimate that was between one-fifth and one-third as much as a conventional targeted exterior repair project would've cost.

Survey before the work starts. I recommend that if you have leaks or if you know you're going to be doing an exterior repair project, you should survey the apartments before the work starts. Why? Because a lot of co-op shareholders and condo unit-owners don't even notice when they have water damage. And once you finish an exterior repair project, it’s too late to go back and do a repair from the exterior.

Boards typically do exterior repairs for three reasons: to fix potentially unsafe conditions; to improve the appearance of the building; or to stop leaks from the exterior. You can usually tell visually if you've solved the first two problems, but you cannot tell visually whether you've stopped a leak or not. That’s why we surveyed the water damage in both of these buildings before we started. That helped us pinpoint the problems and get the jobs done right.