My company, R Corbo Improvements, specializes in remodeling inner-city row houses in Greater New York City and New Jersey area. For the last few years, our work has largely centered around rehabbing the lower two floors (of these four-story homes) into modern kitchen and living-room spaces. An important part of the renovations has been to introduce natural light into these long, narrow homes by opening up the entire back wall and installing large slider doors (see “Revitalizing an Urban Row House,” Mar/16).
Our remodeling work is usually confined to the building’s original footprint, but we’re occasionally asked to build an addition. For this story, I’m going to focus on the steps we took to build a 15-foot-wide-by-18-foot-long two-story block addition. Though we’ve built a few row-house additions in the past with other code-compliant noncombustible materials, such as structural steel studs with exterior gypsum board, we prefer to lay up block walls.
Documenting existing conditions. When you’re working in an urban environment with tight lots and shared party walls, it’s best to foster a cooperative relationship with your client’s neighbors. Prior to construction, I have a meeting with the abutting neighbors in their homes to review what our client’s goals are. This is more than a courtesy call. It allows us to swap contact information to keep the lines of communication open, while also giving me the opportunity to check out the condition of their homes. I want to avoid being wrongfully accused of cracking a wall, or worse, so I take photos of the neighbor’s property and of the city-owned sidewalk area out front to establish a baseline of preconstruction conditions.
Case in point, on this project, we started out by demolishing an existing 8-by-10-foot block addition off the kitchen. While removing the addition’s block frost walls, we noticed the neighbor’s two-story addition was built on top of an old, undersized footing. Hoboken row houses typically had one-story additions (similar to the one we removed), which served as kitchens back in the day. Around the time the neighbor’s two-story addition was built, some 30 or 40 years ago, Hoboken was a depressed area. Row houses were haphazardly split up into multifamily homes and boarding houses, and often the work was not done under any municipal supervision. Upon discovery, we notified the project architect and photographed the neighbor’s marginal footings.
Building After a Storm of Regulations
The architect’s initial structural design called for a crawlspace under a framed first floor supported by block frost walls, but the city’s zoning administrator made us switch to slab-on-grade construction. I can only guess the reason was to avoid having mechanicals located below grade and thus susceptible to flooding. On a lot of levels, we’re still dealing with the aftermath of Hurricane Sandy, which flooded 60% of Hoboken for days in 2012. Many new building regulations were passed in the wake of that event. The resulting structural redesign called for a heavily reinforced 6-inch-thick slab tied into heavily reinforced frost walls and two-story block walls—this was a beefy shell.
Buckets and wheelbarrows. All the demolition and masonry work was jointly coordinated by our project foreman, Danny DoCouto, and our masonry sub, Victor Bezama, of FPV Contracting Co. Working in the city, we don’t have the benefit of using excavation equipment. Our foundation prep work is done old-school—by hand with shovels. All demoed rubble and excavated soil had to be carried out in buckets and wheelbarrows through a garden-level (basement) front window or door. Conversely, all building materials, such as block and concrete mix, had to be carried in by hand or wheelbarrow from small staging areas on the street-side sidewalk.
The foundation. We excavated down to the neighbor’s footings on either side of our planned addition, then formed our new 12-inch-by-30-inch footings against them. For the footing-to-frost-wall connection, we tied vertical #5 L-shaped rebar 2 feet on-center to the footing’s continuous #4 rebar. We placed 1/2-inch XPS foam against the existing walls as a bond break, then wheelbarrowed in concrete from a mixer truck parked street-side.
Our 12-inch-block frost walls were placed about an inch away from the neighbor’s existing walls—they sat off-center on the outside edge of the new footings. We installed galvanized metal truss reinforcement on top of the second course to provide lateral strength. After we laid up three courses, we placed 2-inch XPS rigid foam on the block’s interior face, then leveled and compacted the under-slab native soil. We infilled with crushed stone to the top of the frost wall, then installed 2-by stock to form the slab’s edge.
For the under-slab insulation, we placed 2-inch XPS rigid foam over the crushed-stone base and taped the seams. The architect’s structural redesign called for a robust 6-inch-thick slab reinforced with two layers of heavy-duty welded wire mesh tied into the 12-inch-thick-block frost walls, with #5 L-shaped rebar placed 12 inches on-center.
Block walls. The two-story-plus-high walls were built with 8-inch block. We ran continuous #5 rebar, placed 2 feet on-center, from the footing to the top of the wall and infilled the block cores with mortar at the vertical rebar locations. As we laid up the wall, we incorporated two W8 steel I-beams into the blockwork. The I-beams served as lintels for the addition’s opened-up back wall (large slider doors provided abundant natural light into the home).
At the second-floor and roof levels, we installed bond-beam courses, which helped tie the walls together and provided solid masonry for anchoring our flush-framed floor and roof ledgers to the wall. A third bond beam was installed at the top of the wall. We ran continuous horizontal #5 rebar in the bond-beam channel (tied to vertical rebar), then grouted the channel solid with mortar.
Flush-framed joists. For the addition’s parlor-level (second floor) framing, we installed 3x10 joists flush framed to 3x10 ledgers anchored to the block wall’s bond beams. The architect’s initial design called for the 16-inch-on-center floor framing to be left exposed to the garden-level (basement) living room below, but we ended up covering the ceiling with drywall to hide wiring and mechanicals.
Prior to lifting and securing the 3x10 ledgers in place, DoCouto installed the joist hangers and applied peel-and-stick to the back of the ledger, then predrilled holes for the expansion bolts. Of note: We followed the structural plans and drilled the holes in-line (rather than in a staggered pattern) and later got dinged by the building inspector for the ledger fastening. The architect had to provide a letter to the city stating that the 3x10 ledgers were structurally sound and wouldn’t split.
DoCouto held the ledger in place with 2x4 bracing and then injected Hilti HIT-HY 70 two-component epoxy into the holes with a Hilti HDM 500 manual dispenser gun. He then inserted the expansion bolt, tightened it down, and moved on to the next one. After a little while, the anchor connections hardened like a rock, and we were able to frame the floor.
We flushed-framed the roof similarly, but with TJIs and an LVL box-out for a skylight. Our roof system consisted of a plywood deck with tapered roof insulation (pitched toward a corner roof drain) and a TPO single-ply membrane.
Exterior cladding. We finished off the exterior with brick veneer on the rear façade, and stucco on the right-hand side. For the stucco, the neighbors allowed us access to work from their deck, which was in marginal shape. But I took lots of “before” photos to document its condition and carefully protected the deck from any damage, so we managed to finish without incident.