Room and garage additions that start with the right foundation

Joining a new foundation to a hundred-year-old one

The seam between house and addition is where trouble shows up, and it's decided below grade. When your house was built, the crew dug wider than the basement wall and filled that gap back in afterward. That strip of old backfill is softer than the undisturbed ground past it, so a new footing has to go down through it and bear on firm native soil, or on fill placed and compacted to carry the load.

We also have to dig next to the existing footing without undermining it. If the new foundation goes deeper than the old one, say a basement addition beside a house on a crawl space, the cut can't simply drop below the old footing; that stretch gets underpinned or the new footing is stepped so the original never loses the soil under it. If the new footing sits higher, beside a full basement, it has to reach down through the old backfill or be designed to span it.

Then comes the connection. Depending on the design, the new footing and wall are either pinned to the old foundation with steel dowels drilled and epoxied into the existing concrete, or kept separate with an isolation joint so each side can move on its own. With older Buffalo houses we check what the old wall is made of first, because stone, brick and early block don't hold anchors the way a poured wall does.

Basement, crawl space or slab under the new room

The foundation type decides how big the dig gets. A full basement under the addition gives you storage or finished space and can open into your existing basement, but it's the deepest excavation, the most soil to haul away and the most wall to waterproof. A crawl space uses shorter block or poured walls on footings set below frost, keeps plumbing and ductwork reachable, and suits many bedroom and family-room bump-outs.

A slab on grade is common for attached garages and many sunrooms: the slab rests on compacted stone inside a perimeter of walls or footings that reach frost depth. Where the native clay is stiff enough that a narrow footing trench keeps its shape, a trench pour is another route: dig to depth, then fill the trench itself with concrete, no wood forms. It's quick, but wet or sandy pockets that slough into the trench rule it out.

New York also sits entirely in the code's severe weathering category, which raises the strength and air-entrainment requirements for concrete exposed to the weather, so the mix is ordered to match. In Buffalo the city inspects footings and foundations, then separately inspects the preparation for a concrete slab, so the base gets checked before the pour. Our foundation and basement work covers each of these types.

Lake clay, frost and the soil test question

New York doesn't publish one frost depth for everyone. Under the state residential code, each local jurisdiction sets the minimum footing depth, and a Department of State bulletin lists what goes into that number: how hard the air freezes, what the soil is, how high groundwater sits, and local records and field experience. Cheektowaga's permit packet, for example, draws deck piers at least 42 inches below grade. We confirm your city, town or village's number before a single form goes in.

Depth is only half of it. In Amherst, the Onondaga Escarpment runs roughly parallel to Main Street (Route 5), and the flat lowland north of it is mostly fine-grained silt and clay laid down in glacial lakes. The Erie County soil survey calls those deposits generally highly compressible and prone to settling over long periods, and like most clays they swell when wet and shrink as they dry. A joint study by the Town of Amherst and the U.S. Army Corps of Engineers placed most of the town's damaged houses in that lowland, on the fine-grained lake deposits.

The state residential code provides for soil tests where ground is likely to be expansive or compressible (Section R401.4), and the study reported that Amherst required soil testing before permitting any new house north of the escarpment. If your addition sits on that ground, confirm with the building department whether it wants a soil report. On the dig itself, we keep the footing trench from filling with water or freezing, and we don't pour onto mud or frozen ground.

What's buried where the addition will sit

The yard behind or beside a house is usually crowded underground. Before we dig, we file the 811 location request with UDig NY, formerly Dig Safely New York. State rules set a window for a contractor's request: two full working days ahead at the latest, ten working days ahead at the earliest. Every notified utility has to respond before the machine starts.

The catch: member utilities don't mark private lines on your property. On a typical addition site, those include your own:

• sewer lateral and any cleanouts
• water service
• sump pump discharge and downspout or bubbler lines
• wiring to a garage, lamp post or landscape lights, plus irrigation lines

We find them by tracing each one from where it leaves the house and hand-digging to expose it near the footprint. Lines the utilities do mark get their own rule: inside the tolerance zone, two feet either side of the marked center line plus the pipe's width, they're exposed by hand before a machine digs. Anything that would end up under a new footing gets moved before the pour, because rerouting a pipe in an open hole is simple and rerouting it later means breaking out finished concrete. That can mean a short sewer lateral reroute or moving a water line or conduit as part of our underground utility work.

Buffalo permits, inspections and open trenches

In the City of Buffalo, an addition needs a building permit. One-story detached sheds of 144 square feet or less are exempt; a new room isn't. The application goes to the Department of Permit and Inspection Services with at least two sets of construction documents and, where the work calls for it, a site plan showing existing and proposed structures and their distances to the lot lines. On a narrow city lot, that side-line dimension can end up shaping the addition.

The city inspects in stages, and two of them land on our part of the job: footings and foundation, and preparation for a concrete slab. Work has to stay exposed until it's inspected and accepted, so we schedule the dig to leave trenches open for the inspector and no longer than that. A Buffalo permit also expires if work doesn't begin within six months of issue.

Suburban towns run their own departments with their own paperwork. Cheektowaga, for instance, asks you to draw the addition on a copy of your property survey with dimensions to property lines, easements and existing structures. We confirm what your town wants before the dig goes on the calendar.