Underpinning near you

An underpinning job is an engineering sequence before it is a digging job. The engineer numbers the bays, sets a maximum open length, specifies the order they may be worked in, and states how long a bay may stay open before it is filled. That sequence exists so that the wall above always bridges a short gap onto sound bearing on both sides. When a crew decides in the moment to open two adjacent bays because it is faster, the design has been abandoned whether or not anything falls.

The rest of the day is unglamorous. Each bay is hand-dug or carefully machine-dug to the specified depth, the base of the existing footing is cleaned, the new concrete is placed and then dry-packed tight against the underside of the old footing so the load transfers without the wall dropping to find it. Utilities are located before any of this starts, and monitoring points are set on the building so movement is measured rather than argued about. Ask for the monitoring readings as the job proceeds, not as a summary at the end.

The federal excavation standard is the clearest statement of what underpinning is for. It provides that excavation below the level of the base or footing of any foundation or retaining wall that could reasonably be expected to pose a hazard to employees is not permitted except when a support system such as underpinning is provided to ensure the stability of the structure and protect employees, when the excavation is in stable rock, when a registered professional engineer has approved that the structure is sufficiently removed from the excavation that it will not be affected, or when a registered professional engineer has approved that the work will not pose a hazard.

It then extends the same principle outward. Where the stability of adjoining buildings, walls or other structures is endangered by excavation operations, support systems such as shoring, bracing or underpinning must be provided to ensure the stability of those structures for the protection of employees, and sidewalks, pavements and appurtenant structures may not be undermined unless a support system or another method of protection is provided against their possible collapse. Read that as a homeowner rather than as a contractor and it tells you the two questions to ask any bidder: which registered professional engineer approved this sequence, and what is holding up my neighbor's wall, my sidewalk and my own chimney while it happens.

In much of the country the duty you owe an adjoining owner when you excavate is set by state statute rather than by the building code. California is a useful example because its rule is specific. Civil Code section 832 requires an owner of land, or their lessee, intending to make or permit an excavation to give reasonable notice to the owner or owners of adjoining lands, and provides that the owner of a building or other structure must be allowed at least 30 days, if they so desire, in which to take measures to protect it from damage.

The section then scales the duty with depth. Where the excavation goes deeper than the standard depth of foundations, which it defines as a depth of nine feet below the adjacent curb level at the point where the joint property line intersects the curb, the statute requires that ordinary care and skill be used and reasonable precautions taken to sustain the adjoining land, and that the person making the excavation protect the adjoining land and any building or structure on it from damage by reason of the excavation, without cost to the owner of that property. Your own state's rule will differ in its numbers and its mechanics, and some cities add their own adjoining-property protection requirements on top, so the notice question belongs with your attorney and your building department before it belongs with your contractor. Tell your neighbor early anyway. A neighbor who learns about a nine-foot excavation from the noise is a neighbor with a lawyer.

There is no version of underpinning that is not permit work. The building department wants the engineer's drawings, the bay sequence and the shoring design, and it wants to inspect the excavation and the reinforcement before concrete covers them. That is the only stage at which anyone can confirm the depth reached, the soil the new base is bearing on and the steel that went in, so a job that pours before an inspection has destroyed its own evidence.

Two other approvals commonly attach. Utility locates come first, because the lines running to your house and along the frontage are exactly where the excavation goes. And where the work is next to a sidewalk, an alley or a street, the city usually has a separate permit for undermining or protecting public right of way. Ask for the permit numbers, not for an assurance that permits are handled, and keep the final inspection record with the engineer's letter. Underpinning is the single item a future buyer's inspector is most likely to ask about and least able to verify without paperwork.

Underpinning is sold by the linear foot of wall and bought by the cubic yard of difficulty. The things that move a quote are the depth you are going to and what the soil does on the way down, whether water shows up, how the spoil leaves the site when there is no vehicle access to a city back yard, how much of the work is hand-dug, how many bays the sequence requires and how long each must stay open, whether shoring for a neighboring structure is included, and whether the scope stops at structure or continues into a new slab, drainage and a pump. Engineering, monitoring and inspection fees are real line items and are not the place to economize.

LokalMatch is where the shortlist starts. Describe the job once: what you are trying to achieve, how old the building is, what is next door and how close, whether an engineer is already involved, and how a machine would reach the work. Contractors who do this kind of excavation in your area receive the request, and the ones interested contact you. The service is free for homeowners and paid for by the pros who receive requests. LokalMatch does not perform excavation, does not set prices, and does not vet, rank or recommend contractors, so the engineering, the permits, the insurance check and the notice to your neighbor stay with you.