Launch Slideshow

Beefing Up a Brooklyn Brownstone's Floors and Roof

Beefing Up a Brooklyn Brownstone's Floors and Roof

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    Cramer Silkworth

    New York City architect James Wagner takes a first look at the framing in the 100-year-old brick brownstone townhouse as design work begins for an extensive gut-rehab. The building’s roof will need substantial reinforcement before it will be ready to handle the added loads of a new access bulkhead, a rooftop patio, furniture, and planters.

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    Built in the late 1800s, the house has a staircase hugging the left side of the house, running along a party wall shared with the neighboring building. The wall to the right of the long hallway serves as a “load-relieving wall,” breaking up the span of joists that run across the width of the long, narrow home (the crosswise joists bear at either end on the structural brick party walls that divide the units). When this bearing wall is removed during the remodel, the existing floor joists will need to be reinforced.

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    To reinforce the existing floor, plans called for contractor Jose Maldonado to install light-gauge steel C-joists centered between the existing joists. Leveling the floor was up to Maldonado (engineer Kathy Dunne says the sagging floor was still safe and strong). Maldonado chose to nail 2x6 sisters into the old sagging 3x8 members to create a new top edge that is level with the new factory-straight steel. When the floor is complete, a new light-gauge steel drop ceiling will be installed to create a flat, level ceiling for the room below.

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    Here, a steel C joist is embedded into the brick party wall dividing the row house from the adjacent unit. The existing brick is more than adequate to support the floor and roof loads involved in the renovation. However, the wall is only 2 wythes of brick thick, and is shared with the neighboring home, so work must proceed carefully. Workers remove enough bricks to create a space to insert the new joist, then work non-shrinking grout into the cavity to support the joist end.

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    The section of floor at the left of this image needed reinforcing, but the existing brick was connected to the fireplace chimney of the neighboring unit, and could not be disturbed. So contractor Jose Maldonado worked around the area by installing a header and beam system framed with LVL members. At the right of the photo, where the crew was able to tie into the existing brick, a section of floor has been reinforced and levelled with steel C-joists and 2x6 sisters.

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    This section of the second-floor frame was in bad condition and had to be completely replaced with steel. To the right of the picture, the LVL beam terminates in the brick wall where the crew had to work around the existing chimney belonging to the neighboring unit.

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    On the right side of the new framework that works around an existing chimney, the new LVL member has been bolted to an existing 3x10 sawn floor joist, and bedded into the brick wall alongside the existing member. Project engineer Kathy Dunne says the existing brick structure is more than adequate to handle this kind of new point load, as long as it’s repaired and repointed where necessary. Non-shrinking grout is used to embed the new framing into the walls.

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    Structural issues aren’t the only issue to address with the existing wood framing, says contractor Jose Maldonado. Here, a worker caulks a long crack in a wood joist. This is an air-tightening measure, explains Maldonado: The crack runs all the way to the end of the joist where the wood is buried in the brick party wall. During air-sealing, the brick and the joist ends are sealed with Sto Diamond Cote elastomeric coating; but the crack in the joist can bypass that seal and create a leak that will show up during blower door testing, if not attended to during the framing stage. “I have had that happen before,” says Maldonado.

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    Jose Maldonado’s crew installs PSL (parallel strand lumber) beams around a new roof opening intended to accommodate a bulkhead giving access to the townhome’s roof, where a walkable concrete paver patio will be built. Making the roof into occupied space more than doubles the load on the space when live loads from occupancy and dead loads from pavers, planters, and the like are considered, says project engineer Kathy Dunne. Dunne specified PSL members for the new beams in this location, but she says that LVL (laminated veneer lumber) material would do just as well. “They’re both engineered lumber and their properties are very similar,” she said. “So it’s a carpenter-generated decision. PSLs have the same depth as LVLs, and they come in widths that are multiples of the LVL width. So LVLs are only available in 1-3/4-inch width, and PSLs are 3-1/2, 5-1/4, or 7 inches wide. Well, from a structural engineering standpoint they are interchangeable, typically; so if I say 3-1/2 by 9-1/2-inch PSL, they could put in two 9-1/2-inch LVLs, for all I care.”

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    In a few places, project engineer Kathy Dunne specified a steel flitch plate to augment the load-bearing capacity of the existing floor framing. Here, a steel plate is bolted to the end of a wood joist, and bedded into the wall next to it. Says Dunne: “To stay in the wood vocabulary, you would need an 18-inch-deep beam, and you couldn’t occupy the room below.”

The Brooklyn townhouse project we’re following is a cutting-edge application of the latest energy-efficient technology. Structurally, however, it’s old hat—at least if you’re New York City structural engineer Kathy Dunne, who has been working on brownstones for three decades, or Brooklyn contractor Jose Maldonado, who has been renovating brownstones for twenty years.

But if you’re not that accustomed to working in 100-year-old brick row houses, the project offers a few interesting structural wrinkles. In this set of photos, we take a look at the way the framers reinforce the old, sagging floor joists with new steel framing and engineered lumber, tie that new structural work into the existing brick bearing walls, and beef up the roof structure to handle a whole new set of loads from a rooftop patio and access bulkhead.