What are the different types of underpinning?

Underpinning means strengthening or extending a foundation downward so it rests on stronger soil or deeper support. The main types are mass concrete, beam and base, mini-piled, and pier-based methods like helical piers and push piers. For a settling home in New Hampshire, the pier-based methods get used most. At 603, we install helical and push piers in-house. Helical piers run $2,700 per pier for the first three, then $2,200 per pier after that, and we price that job after we see it.

The basic idea

A foundation can start to sink when the soil under it can’t hold the load anymore. Underpinning fixes that by getting the weight down to soil that can. There are a handful of ways to do it. Which one fits depends on how deep the good soil is, how the house is built, and how much it has already moved.

Here are the common types.

Mass concrete underpinning is the oldest method. Crews dig out sections under the footing in stages and pour new concrete to extend the footing deeper. It works on shallow problems. It’s slow and it means a lot of excavation, so it’s rare on modern homes with finished basements.

Beam and base underpinning builds a reinforced concrete beam to spread the load onto concrete bases set at intervals. It can handle heavier or uneven loads than plain mass concrete. Still a big excavation job.

Mini-piled underpinning uses small-diameter piles driven deep when the strong soil sits far down or access is tight. It suits harder ground conditions.

Pier-based underpinning is the family we work in. Steel piers carry the load past the weak, disturbed soil down to firm bearing. Two kinds matter here. Helical piers are a steel shaft with helix plates, screwed into the ground like a giant screw. The crew torques them in, and the torque tells you the capacity. They work well for lighter loads and new additions, and they install fast with small equipment. We carry a 25-year engineered warranty on ours. Push piers, also called resistance piers, are steel tubes pushed straight down using the weight of the house itself. The structure is then transferred onto them. They suit heavier loads on a settling home.

A couple of related repairs get lumped in with underpinning, though they aren’t true underpinning. Slab support holds up a sinking concrete slab rather than the footing. Wall stabilization with carbon-fiber straps or a power brace fixes a wall bowing inward, which is a different problem from settling. Frost heave here in NH pushes basement walls in, and that calls for stabilization, not piers.

Why settling happens here

Around your foundation sits disturbed backfill. That’s the loose soil that got put back when the house was built. It drains slowly and holds water, and over years it can compress or wash out. When it gives, the footing follows. NH frost cycles add to it. So the fix isn’t always more concrete. Often it’s getting a pier down to soil that was never disturbed.

What drives the cost

Pier work is priced per pier and by depth. The deeper the firm soil, the longer the pier, the more it costs. Number of piers, access, and whether your crew needs to lift the house back toward level all move the number. Helical piers run $2,700 per pier for the first three, then $2,200 per pier after that. For a full foundation-wall rebuild or steel I-beams, there’s no flat price. We price that after we see it.

You may not need underpinning at all

A lot of cracks we get called about are not settling. A clean vertical crack in a poured wall is usually shrinkage, and that’s a crack injection job, not piers. Crack injection runs $1,000 to $3,000. A wall pushing in from frost or soil pressure is a carbon-fiber or power-brace job. Carbon-fiber straps run $850 each and a power brace runs $1,300 per brace. So before anyone talks piers, you want eyes on it. We come look for free and tell you what it is, even when the answer is “you don’t need this yet.”

See our structural and foundation repair and helical piers pages for how each repair works, and the foundation repair hub for the full list. Every job is backed by the 603 guarantee.

For neutral background on foundation soils and drainage, the U.S. Department of Energy’s Building America program (basc.pnnl.gov) is a solid read. For how foundation damage is treated by home policies, see the Insurance Information Institute (iii.org).

Talk to us

Not sure if your house is settling or just cracked? Call us at 603-610-1770 or book your free inspection. We’ll look, measure, and give you a real plan with a quote within 24 hours.

Related questions

Do I need underpinning or just a crack repair? If the wall is sinking or the floor is dropping, that’s a settling job and piers may be the fix. A vertical crack with no movement is usually shrinkage, handled by crack injection at $1,000 to $3,000. A free inspection sorts it out.

What’s the difference between helical and push piers? Helical piers screw into the ground and work well for lighter loads and additions. Push piers are driven down using the home’s weight and suit heavier loads on a settling structure. We install both. Helical piers run $2,700 per pier for the first three, then $2,200 per pier after that.

Does 603 build new foundations? No. We repair and stabilize existing foundations. That covers piers, carbon-fiber straps, power braces, lally columns, and sill and beam work. For a full wall rebuild we price that after we see it.

Is pier work guaranteed? Yes. Our helical piers carry a 25-year engineered warranty, and carbon-fiber wall stabilization carries a 25-year warranty. Floor support and power posts carry a 10-year warranty.