What is underpinning (definition, history, and types)?

Underpinning is the work of strengthening or extending a building’s foundation downward so it sits on firmer, deeper soil. Homeowners reach for it when a foundation has settled, cracked, or sits on soil that can no longer carry the load. At 603 Basement Solutions, the modern version we install is helical and push piers, and we price that after we see your foundation: $2,700 per pier for the first three, then $2,200 per pier after that.

Your house sits on a foundation. That foundation sits on soil. When the soil under part of the house shifts, washes out, or was never strong enough, that section drops. Walls crack. Floors tilt. Doors stop closing right. Underpinning reaches past the weak soil and transfers the load to ground that holds.

The word goes back a long way. For centuries, “underpinning” meant digging out sections beneath an old foundation and filling them with stone, brick, or later concrete to build a deeper, wider base. Crews worked one short section at a time so the wall above stayed up. That mass-concrete method is still used on some historic buildings today. The idea is old. The materials changed.

The history matters because it tells you underpinning is a structural repair, not a basement product. People sometimes mix it up with waterproofing or finishing. Those are different jobs. If your foundation is settling, you don’t need a new floor first. You need the load handled.

Here are the main types you will run into.

Mass concrete is the traditional method. You dig out a section under the footing, pour concrete, then repeat down the wall. It is old, slow, and labor-heavy. Mostly seen on historic or commercial work now.

Helical piers are steel shafts with a helix plate, screwed into the ground like a giant earth screw until they hit load-bearing soil or refusal. A bracket ties the pier to your footing. No big pour, no waiting for concrete to cure. We self-perform these in-house, and they carry a 25-year engineered warranty.

Push piers, also called resistance piers, are steel sections driven straight down using the weight of the house itself as the reaction force, until they reach firm strata. Good for heavier structures.

Beam-and-base and pile methods are larger engineered approaches for bigger or trickier loads. These get designed case by case.

For most New England homes with a settling footing, the practical fix is helical or push piers. That is what we install. The traditional mass-concrete method is real and it works, but it is rarely the right call on a typical NH house.

Why does soil give out here? Often it is the same culprit we see behind wet basements. The ground right against your foundation is disturbed backfill, the looser fill that got put back when the house was built. It settles unevenly over time. Add NH frost. Water freezes, expands, and frost heave pushes and lifts. Over enough winters, a footing on weak fill can drop. That is when piers earn their keep.

Not every crack means you need underpinning. A thin vertical crack from concrete curing is common and often just needs sealing. We handle that with crack injection, and that is priced separately: $1,000 to $3,000. Underpinning is for actual settlement: a wall or corner that has dropped, stair-step cracks widening over time, floors going out of level. If you are not sure which one you have, that is what the free inspection is for. We would rather tell you it is minor than sell you piers you don’t need.

When piers are the answer, the load gets transferred to stable ground and, in many cases, the foundation can be lifted back toward level. We pair piers with the rest of our structural and foundation repair work, including helical piers and supplemental floor support, and every repair is backed by the 603 guarantee.

For background on settlement, ground movement, and how soil affects foundations, the U.S. Department of Energy’s Building America program is a solid neutral reference (basc.pnnl.gov [verify]). For how foundation issues interact with home insurance, the Insurance Information Institute (iii.org) is worth a read.

One note on scope. We do foundation repair, not new foundations. If you are building from scratch, that is a different trade. If your existing foundation is settling or failing, that is our lane.

Want to find out which type of repair, if any, your house actually needs? Call us at 603-610-1770 or book your free inspection. We will look, tell you what we see, and get you a quote within 24 hours.

Related questions

How do I know if my foundation needs underpinning? Look for settlement, not just any crack. Stair-step cracks that keep widening, a wall or corner that has dropped, floors out of level, and doors or windows that suddenly stick. A thin vertical crack alone usually just needs sealing. A free inspection sorts it out.

Are helical piers better than push piers? Neither wins across the board. Helical piers screw into the soil and work well on a wide range of homes, which is why we install them in-house. Push piers use the home’s own weight to reach firm strata and suit heavier structures. The soil and the load decide. Helical piers carry our 25-year engineered warranty.

Does underpinning fix a wet basement? No. Underpinning is a structural fix for settlement. A wet basement is a water problem, handled by our Forever Dry System of interior perimeter drainage, a sump pump, a vapor barrier, and a dehumidifier. Different problem, different fix. Some homes need both.