What piering does
Piering, also called underpinning, transfers the weight of a house from weak or shifting soil near the surface to deeper, more stable soil or bedrock. Steel piers are driven or screwed into the ground beside or beneath the foundation, then connected to the footing with brackets. Once installed, the piers support the house, and in many cases they can be used to lift a settled section back toward its original level.
Piering is used for foundations that have settled because the soil beneath them compressed, washed out, dried and shrank, or was never compacted properly. It's a structural repair and usually one of the more significant foundation repairs a house can need.
Signs that a foundation may need piering
- Stair-step cracks in brick or block walls, or diagonal cracks spreading from the corners of doors and windows.
- Cracks that are wider at one end than the other, or that have one side higher than the other.
- Doors and windows that stick, won't latch, or have uneven gaps at the top.
- Floors that slope noticeably toward one corner or wall.
- Gaps between walls and ceilings or floors, or between the house and a chimney or porch.
- Cracks in the foundation that keep getting wider over months.
Many of these signs can have other causes. That's why an assessment matters.
Push piers versus helical piers
- Push piers (resistance piers) are steel tubes driven hydraulically into the ground in sections, using the weight of the house as resistance, until they reach a stable soil layer. They work well for heavier structures.
- Helical piers are steel shafts with screw-like plates that are twisted into the ground with a hydraulic motor. They're suited to lighter structures, such as porches, additions and decks, and for new construction, and can be installed where loads are lower.
Other methods, such as concrete pilings and mass concrete underpinning, are also used in some situations. The right choice depends on the soil, the depth of stable material, the weight of the structure and access around the house. An engineer's recommendation is valuable here.
Lifting: what to expect
Piering can often lift a settled part of the house toward level, but it doesn't always return it to perfectly level, and lifting can open or close existing cracks in drywall and change how doors fit. A good contractor sets expectations in writing: what they'll attempt to recover, how they'll monitor the lift, and what cosmetic repairs you should expect afterward.
Engineering and permits
Structural foundation repairs often require a permit, and many contractors work with a structural engineer who evaluates the problem and specifies the repair. An independent engineer's assessment, separate from the company selling the repair, can be worth the cost before a major job, especially if quotes differ widely in what they recommend.
Fix the cause too
Piering addresses the result of soil problems. The causes, such as poor drainage, leaking pipes, downspouts dumping water at the foundation, or trees drawing moisture from clay soil, should be addressed too, or other parts of the foundation may move.
Questions to ask
- What's causing the movement, and how did you determine it?
- How many piers do you recommend, where, and how deep will they go?
- Will you attempt to lift, and how much recovery do you expect?
- Is an engineer involved, and will there be a permit and inspection?
- What does the warranty cover, and is it transferable if I sell?