Abacus

Abacus Builders is the South Boston shop people call when the problem is the outside of the building — a roof deck, a porch two stories up, an envelope letting water into the units. Mark Little started the company in 2006 and opened the Old Colony Ave office in 2014, by its own account. On Google it averages 4.9 across 87 ratings, and the work customers describe most is structural and exterior. In an October 2025 review, a homeowner had the roof deck rebuilt after the old one came down for a roof replacement, and the reason they picked Abacus was blunt: other contractors had "hedged on this, hedged on that, wouldn't give straight answers." A December 2025 customer had every deck board replaced in one day plus exterior painting, on an estimate that came in lower than other contractors and with no change orders. In April 2026, another had a full stair repair on exterior egress stairs and said the crew came back to fix an issue that arose during the work. The bigger jobs run long and complicated. A development company brought Abacus in, per a July 2025 review, to finish a South End condo conversion — a five-unit apartment building becoming two duplexes and a single condo — after another general contractor started the demolition and did not complete it. In a 2024 review, new owners of an old Beacon Hill condo hired them to fix an unpermitted, defective partial rebuild of a rear porch nearly two stories off the ground, with the back of the building reachable only through a tunnel. Another 2024 reviewer named five Abacus people, plus the electricians and plumbers, on a nine-month full renovation of a South End row house. They build for themselves as well: a 2025 news item reported Mark Little filing with the city's Planning Department for a six-story mixed-use building with a ground-floor restaurant and no on-site parking, and in 2024 a neighborhood news post carried a sailing center board's thanks to him and his crew for a new dock. Ask how drawings get to subcontractors. A February 2024 reviewer had nothing but praise for the crew at the condo daily building the roof deck, then said Abacus gave the ironworkers the wrong plans and the spiral staircase was built and installed on the wrong side of the house. On price, the one four-star reviewer, who had the roof, siding and trim redone in November 2025, put them between the cheapest and the most expensive bids and said the price felt reasonable after seeing how much work was done. For exterior and structural work on older Boston buildings — decks, porches, stairs, envelopes — or a gut job another contractor left half-finished, this is a straightforward call. Before any ironwork or off-site fabrication, get it in writing which drawings the subcontractor is building from and who approves them.