Pier Foundations

Piers Can Support Anything From a Deck to a House

UPDATED 11/27/2012

Bird's eye view

For use with unusual soils or steep slopes

Concrete piers foundations save time and money because they don’t require extensive excavation or a lot of concrete. Simple pier foundations resemble those used for residential decks. If the site has unusual soils or is steeply sloped, or the house has unusually high loads, an engineered foundation is required.

See below for:
ENGINEERED OPTIONS


Key Materials

Cardboard and plastic footing forms

For a simple foundation, a concrete footing can be poured by placing concrete directly into the bottom of the hole. When soil conditions require a form, many builders choose round plastic footing forms like the Bigfoot system (www.bigfootsystems.com), designed to accommodate different diameters of cardboard Sonotubes.

The Footing Tube (shown) integrates the footing form and pier form into a one-piece system.
The Footing Tube


Design Notes

Discussing foundation options

Builder Mike Martuscello (MGM Construction) talks with and structural engineer Bruce King and Peter Yost of GreenBuildingAdvisor.com about integrated designBuilding design in which different components of design, such as the building envelope, window placement and glazings, and mechanical systems are considered together. High-performance buildings and renovations can be created cost-effectively using integrated design, since higher costs one place can often be paid for through savings elsewhere, for example by improving the performance of the building envelope, the heating and cooling systems can be downsized, or even eliminated. and weighing foundation choices for a site in a seismic region. Seismic considerations narrowed the choices. But the owners of this house wanted the house to go beyond seismic-resistance. They wanted to house to be capable of providing refuge for many in such an event. It should be Earthquake-proof and provide passive survivability.

One choice was a thick reinforced "mat slab" that would allow the house to "float" on the surface. Another was a pier and grade-beam foundation that would anchor the house to it. Both would work, but the environmental consequences of each type was surprising.

The floating slab seemed like the less intensive route, but when all things were factored in, the pier and grade-beam foundation was greener, and a lot less expensive.


Builder Tips

Frost-proofing a pier foundation

Concrete-column construction can cause problems in cold areas due to freeze-thaw cycles. But this system can be great if you do it right. As frozen soil heaves in the winter, it can grab the cardboard column form and cause it to lift or to shift slightly. When the ground settles back, the column can be left tilted. Even if you peel off the cardboard, frost is good at grabbing concrete.

To combat frost, do two things
Builder Lynn Hayward of Northport, Maine recommends a couple of strategies to minimize the effects of frost:
1. Control frost action as much as you can;
2. Give the frost something to grab so that it leaves the column alone.

As shown in the drawing, you can keep frost action low by backfilling around a column with crushed stone and gravel; this process helps to drain water away from the column. You also can buffer the ground temperature with foam insulation. Columns on the south side of a foundation experience more freeze/thaw cycles than those on the north side because the sun beats on them during the day. A layer of insulation will keep the sun’s heat out of the ground.

To keep frost from grabbing the column, use a sleeve. In the old days, Hayward used schedule-20 sewer pipe as a sleeve. The frost would grab the sleeve, but the column itself would not move.

He's also wrapped the column with plastic sheeting up to ground level. The plastic acted as a sleeve so that the frost couldn’t grab.

A new product that incorporates the footing, pier, and frost-proof sleeve all in one does a good job of accomplishing Hayward's two goals. It’s called the Footing Tube. Rather than cardboard, the tube is made of high-density plastic, so frost can’t bond to it. The footing base is built in. All you need to do is set the form in a hole, cut off the top to the desired height, backfill, and pour concrete.


The Code

Footings a minimum of 12 inches below grade

According to the IRCInternational Residential Code. The one- and two-family dwelling model building code copyrighted by the International Code Council. The IRC is meant to be a stand-alone code compatible with the three national building codes—the Building Officials and Code Administrators (BOCA) National code, the Southern Building Code Congress International (SBCCI) code and the International Conference of Building Officials (ICBO) code., piers — like other foundation types — should have footings placed a minimum of 12 inches below undisturbed grade (403.1.4) and protected from frost (403.1.4.1). The bearing capacity of soils underneath a pier should be based on a soils test or IRC Table 401.4.1 which identifies the load-bearing capacity of five soil types from clay (1500 psf) to crystalline bedrock (12,000 psf).

OTHER CONSIDERATIONS

You have to give lots of thought to the underside of the first floor of a house built on piers because of its exposure to the outdoors. Like other parts of a home's shell, a pier-built house's floor system will have to be insulated, waterproofed, and air-sealed.

Fiberglass batts perform poorly here unless they fully fill the cavity and are enclosed on all sides by a tight air barrierBuilding assembly components that work as a system to restrict air flow through the building envelope. Air barriers may or may not act as a vapor barrier. The air barrier can be on the exterior, the interior of the assembly, or both.. For more information on insulating a building on piers, see How to Insulate a Cold Floor.

GREEN POINTS

LEEDLeadership in Energy and Environmental Design. LEED for Homes is the residential green building program from the United States Green Building Council (USGBC). While this program is primarily designed for and applicable to new home projects, major gut rehabs can qualify. -H 1/2 point available under MR2.2 (Material & Resources) for fly ashFine particulates consisting primarily of silica, alumina, and iron that are collected from flue gases during coal combustion. Flyash is employed as a substitute for some of the portland cement used in the making of concrete, producing a denser, stronger, and slower-setting material while eliminating a portion of the energy-intensive cement required. National Green Building Standard Based on the NAHB Model Green Home Building Guidelines and passed through ANSI. This standard can be applied to both new homes, remodeling projects, and additions. Under Ch. 6 — Resource Efficiency: 3 pts. for use of a foundation system, such as piers, that is considered resource-efficient (601.8); up to 4 pts. for recycled-content (fly ash or slag substitution for Portland cement in concrete) (604.1).

ABOUT PIER FOUNDATIONS

Disturbing as little soil as possible
Pier foundations are unlike more conventional concrete footings and walls in that they support structural loads at a number of distinct points, not continuously. Pier foundations can be as simple as concrete-filled cardboard tubes dropped into hand-dug holes. But more complex foundations incorporating very deep piers or helical screws can support much greater loads.

To some green builders, one advantage of pier foundations is that they cause minimal disruption to the soil environment. Excavation can be performed with a shovel, and existing roots and soil organisms remain mostly undisturbed. At the end of the building's useful life, the site will be easier to restore to a natural state than a site with a full basement.

Design starts in the soil
The number and size of the piers depends on how much weight the underlying soil can hold. The standard design load in the International Residential Code assumes a 40-pound live load; dead load is commonly calculated at between 10 and 15 pounds per square foot, depending on the materials used for construction.

Hard-packed gravel may be able to handle as much as 3,000 psf while soil with high clay content or lots of organic material will support much less weight. Recommendations of the IRCInternational Residential Code. The one- and two-family dwelling model building code copyrighted by the International Code Council. The IRC is meant to be a stand-alone code compatible with the three national building codes—the Building Officials and Code Administrators (BOCA) National code, the Southern Building Code Congress International (SBCCI) code and the International Conference of Building Officials (ICBO) code. are summarized in a table (referenced in the code as 401.4.1). In situations where the bearing capacity of the soil is questionable, it may be necessary to call in a soils engineer for help.

MORE ABOUT PIER FOUNDATIONS

Engineered options

The most basic foundation consists of a series of concrete posts bearing on concrete footings installed below the frost line.

Pier foundations, however, can be far more complex. On steep or unstable sites, pier and grade-beam foundations are an option when conventional foundations won’t work. These consist of a series of concrete piers, extending up to 20 ft. into the ground, connected by horizontal concrete beams. These foundations require careful engineering, along with a good deal of reinforcing steel and concrete. But they allow building on sites where conventional techniques would not.

Helical screws, another type of specialized pier foundation, can support foundations in soils with low load-bearing capacity. They consist of a steel shaft with helical plates welded onto it that are turned into the ground with hydraulic motors. They can be used in tension (as in a telephone pole guy wire support) or in compression, as they would in a foundation. They can be used in new construction on lots with poor soil, or to save foundations on existing houses that are sinking into the ground.

FURTHER RESOURCES

Building on Piers, Fine Homebuilding

How to Insulate a Cold Floor


Image Credits:

  1. Dan Thornton/Fine Homebuilding #180
  2. Chris Ermides/Fine Homebuilding #180
  3. Dan Thornton/Fine Homebuilding #169
Tags: , , ,
4.
May 13, 2010 5:54 AM ET

Concrete piers in a crawl space
by Martin Holladay, GBA Advisor

Anonymous,
It's impossible to answer your question without a site visit.

You need to consult an engineer and an experienced contractor.


3.
May 12, 2010 8:29 PM ET

piers
by Anonymous

I may need to install a few piers for a third floor addition on a house , i have one pressure point from roof load that my require under pinning of the foundation. Is there any compony that can instal piers inside of house crawl space. Truss company says there is a load of maybe 25000 lbs at one spot. Can one pier support that much wieght or does it take many ? job is in eastern ontario canada


2.
Mar 31, 2010 5:24 AM ET

Foundation engineering
by Martin Holladay, GBA Advisor

Anonymous,
If you live in an area subject to building codes, you clearly need to consult with an engineer. The answer to your question depends on local soil conditions, frost depth, and the characteristics of your house.

If you live in a rural area that is not subject to building codes, you need to purchase and study a collection of basic construction manuals before you begin building. Even a simple, classic book like the 1969 volume, "Low-Cost Wood Homes for Rural America: Construction Manual" (U.S. Department of Agriculture) will get you started.

In other words, if you aren't sure about how to build a foundation, you're tackling a job that may be over your head — at least until you do some more studying.


1.
Mar 31, 2010 3:31 AM ET

house foundation
by Anonymous

I am building a home & thinking of using peir & beam . A ny suggestions on using cardboard tubes for concrete forms ? I plan on using concrete from a batch plant to get a quality mix . My only concern is how far apart to put the peirs &what diameter to use . My plans are about 1800 sq.ft. one story 3 bed room house w/a low pitch normal roof plan


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