When constructing a building, the foundation is arguably the most important part. It’s the base that keeps the entire structure stable and supported. Pier foundations are commonly used for houses, decks, sheds, and other lightweight buildings.
So, what are the pier foundation types? There are four: column, wall, t-shape, and pin.
With pier foundations, the weight of the building is concentrated onto piers or footings spaced out beneath the floor. This article will focus on the four basic types of pier foundations and what makes each one unique.
The most basic type of pier foundation involves using a concrete column or footing under posts to transfer the load into the ground. These piers are typically made by digging a hole and pouring concrete to form a wider foot at the bottom than the top. A steel post or support beam is then anchored into the cured concrete to provide support for the structure above.
Column piers work well for patio covers, decks, porches, and other structures using post-and-beam construction. They provide a simple, inexpensive foundation option when you just need to support vertical posts in the ground. The main drawback with column piers is they concentrate the load in one spot, which can lead to settling if the soils are too soft or unstable.
Wall piers are more effective for foundations under bearing walls, such as stem walls for a shed or crawl space walls for a house. These use individual footings placed at regular intervals under the wall. Wall piers help minimize settling and differential movement by spreading the load across multiple piers.
Wall piers are wider than a typical column pier, usually about 18-24 inches square. They are also placed deeper in the ground, often at or below the frost line for colder climates. The piers can be tied together with grade beams if additional lateral support is needed.
T-shaped piers provide added shear resistance due to their wide top section extending out past the main column. This wider cap helps resist wind, earthquake, or soil movement lateral forces. The top section is typically double the width of the base column, creating the T-shape design.
These types of piers are often used in seismically active areas where lateral loads are a major design concern. The pier is able to better distribute shear across its width. Reinforcing steel rebar is usually installed to strengthen it further against horizontal stresses.
Constructing T-shape piers requires building full-depth wooden forms to contain the concrete for the top cap. Additional rebar must also be bent and tied to reinforce this cap section. The cost and construction time are more than a plain rectangular pier footing.
The major advantage of the T-shape is the sheer resistance in multiple directions. This helps stabilize foundations against seismic activity and soil issues like liquefaction. Providing strength against horizontal loads as well as vertical makes T-shape piers ideal for at-risk sites.
Pin piers, also called screw piers or helical piers, offer height-adjustable foundation support. They use a screw anchor design with a helical steel plate welded to the end of a steel shaft. The anchors are screwed into the ground and can be adjusted by turning the head after installation.
Did you know pin piers are often used when retrofitting foundations for settling structures? Damaged piers can be replaced without having to lift the building. These types of piers work in difficult soils and can be installed quickly with minimal equipment. However, they don’t offer as much shear resistance as a wider concrete pier.
Selecting the optimal pier foundation involves considering several key factors:
A thorough soil analysis and geotechnical report should guide appropriate pier selection. An engineer can then design the optimal pier size, depth, spacing, and reinforcement needed. Customizing piers for your site’s specific conditions results in the most stable and cost-effective foundation.
About Better Foundation Repair Corpus Christi
Better Foundation Repair Corpus Christi is a trusted foundation repair company serving homeowners in the local and surrounding areas. With over 25 years of experience, their team of experts can diagnose and repair all types of foundation problems, including sinking concrete slabs, crawl space issues, and more. To discuss your foundation repair or leveling project, call (361) 480-0823 for your free inspection and estimate.
What is the difference between a pile foundation and a pier foundation?
Pile foundations use deep foundations like driven piles or drilled shafts that extend down through soft soils to stronger layers or bedrock. Pier foundations rely on shallow footings or piers that transfer loads further up into firmer soils. Pile foundations can provide support in weak soils and resist uplift forces, while pier foundations work best in stable soils close to the surface. Pile foundations require more specialized equipment to install the deep supports compared to pier foundations, which use simpler shallow excavations.
How deep should pier foundations be?
The depth of pier foundations depends on several factors, including soil conditions, climate, and loads. In cold climates, pier footings must extend below the frost line to prevent heaving during freeze-thaw cycles. In most cases, pier foundations should be a minimum of 24 inches deep for light loads or up to 10 feet deep for heavier loads. Digging test holes during site analysis helps determine the depth of stable soil and potential for scouring during floods, guiding appropriate pier footing depths. Building codes provide further guidance on minimum foundation depths based on site-specific conditions and pier spacing.
What is the strongest type of foundation?
The strongest and most robust type of foundation is a pile foundation, which uses deep pillars or piers embedded into the ground. Pile foundations can transfer structural loads through soft or unstable soils to reach hard rock or denser soil strata. They provide great strength against heavy vertical and lateral loads as well as uplift forces from wind or earthquakes. However, pile foundations require expensive installation using heavy equipment. They are overdesigned for smaller residential projects, making shallow foundations more practical for typical homes.