Sidewalk vault waterproofing for Jersey City brownstones and rowhouses

Walk to the front of the basement in many downtown Jersey City and Hoboken rowhouses and you'll find a low room running out under the stoop, or past the property line beneath the sidewalk. These vaults once held coal, ash cans and storage. Their walls are brick or rubble stone laid in lime mortar, and the ceiling is usually a shallow brick arch or stone slabs resting on iron beams, with the sidewalk paving sitting right on top.

That ceiling is the main problem. A sidewalk slab takes rain, snowmelt, de-icing salt and every freeze-thaw cycle of a New Jersey winter, and the paving above a vault was never built to work as a roof. Joints open, flags settle, and water runs straight down into the brick below. The round coal-chute opening, usually capped with a cast-iron cover, leaks around its rim, and old pipe and conduit holes through the vault wall let water track in beside them.

The third leak point is the joint where the vault meets the house foundation. The vault and the house were often built at different times and settle at different rates, so a crack opens along that line. Water following the slab or the areaway wall finds the crack and runs down into your front basement wall. On low blocks near the old Hudson marsh, groundwater can also press in through the lower courses of the vault after long rains.

The surest fix for a leaking vault ceiling is stopping water before it ever reaches the masonry. Where the paving can be lifted, our crew takes up the sidewalk flags or breaks out the slab over the vault, cleans the top of the arch or deck, and resets loose brick. Then we apply a sheet or liquid-applied membrane across the whole vault roof, lap it up the house wall and over the vault edges, and lay a protection board before the new paving goes down.

The coal-chute opening gets the same attention. We either reset the cast-iron cover on a new frame with a flashed, sealed rim, or close the opening beneath the cover with masonry and membrane so the cover stays in the sidewalk as part of the streetscape. Opening a public sidewalk usually involves the city, so we tell you up front when we expect a permit. On historic blocks we also tell you when the work will likely go through Historic Preservation Commission review.

Staging matters on these jobs. Rowhouse blocks downtown have narrow sidewalks, steady foot traffic and permit parking at the curb, so we plan barriers, a protected walkway past the work and a place for debris before the first flag comes up. Most topside jobs open only the part of the sidewalk over the vault, and the new paving is finished to sit flush with the slabs on either side so nobody trips on the seam.

Sometimes the sidewalk can't reasonably be opened, or the leak is small enough that it isn't worth it. From inside the vault we work on the masonry directly. Active cracks and joints in the ceiling get polyurethane injection, which expands and seals even while water is still coming through. Where the whole ceiling seeps, curtain injection pumps grout through the masonry into the soil and paving bed above, building a water-blocking layer on the outer face of the vault.

Washed-out lime mortar in the vault walls is raked and repointed with a lime-based mortar, the same approach we use on stone and brick foundations. Pipe and conduit penetrations are sealed with hydraulic cement or a compression seal. At the joint against the house, we inject the crack and, where it keeps moving with the seasons, finish it with a flexible sealant that stretches with the two structures instead of reopening.

Every vault also needs somewhere for water to go. If the floor is dirt or broken brick, we pitch a new floor toward a small drain or a sump. Where that drain ties into the building's sewer line, a backwater valve keeps combined sewer water from rising up through it in a storm. A vault that drains dries out between rains, which also slows the rust on any iron beams overhead.

Many vault ceilings rest on iron or steel beams, and a century of dripping water can rust them badly. Rust swells as it builds up, which pushes brick out of the arch and opens more paths for water. When we find beams with heavy section loss, a sagging arch or loose stone slabs, we have a structural engineer look at the vault before sealing anything, and we build the waterproofing around the repair they specify.

A vault rarely leaks alone. The sunken areaway in front of the basement door shares walls with it, and the same stoop sheds water onto both. We often seal the areaway walls and clear its drain on the same visit as part of areaway and stoop waterproofing. If water also shows up along the rest of the front foundation, our guide to why Jersey City basements leak walks through the other usual suspects.