Simple Pier Foundations

Simple pier-and-grade-beam foundations can support decks, porches, pole barns, and small home additions, providing good insulation and ventilation (below).

Figure: Simple Pier Foundations
Sonotubes, placed on pier footings with a pressure-treated grade beam, can be installed easily without disturbing existing utility lines.
Sonotubes, placed on pier footings with a pressure-treated grade beam, can be installed easily without disturbing existing utility lines.


Sizing Piers 

For sizing pier diameters for small foundations, the rule of thumb is “1 inch per foot of span.” Thus, a deck that spans 8 ft. will stand comfortably on 8-in.-diameter piers, while a deck that spans 10 ft. requires 10-in.-diameter piers. For spans longer than 12 ft., add a second row of piers and a second girder at the center of the joist span.

For calculating concrete amounts, see Estimating Concrete for Piers.


Pier Footings

Footings for shallow piers (less than 6 ft. deep) will help prevent the pier from settling. The pier footing should be as thick as the pier’s diameter, with sides that measure twice that much. So an 8-in. pier, for example, should rest on a footing that’s 8 in. thick and 16 in. square, while a 12-in. pier should rest on a footing that’s 12 in. thick and 24 in. square.


Simple Pier Foundation Details

  • Use strap ties to anchor piers to a triple pressure-treated 2-by girder. The ties wrap around the center stick in the built-up girder and lap over the top. (The girder looks better if the ties aren’t exposed on its face.) 
  • Install a poly vapor barrier over the ground beneath the joists, and run it up and staple it to the inside of the girder. This helps prevent water vapor from building up in the shallow space beneath the joists.
  • Additional moisture control can be added by cantilevering joists 2 in. beyond the rim of the girder, and installing a 2-in.-wide standard metal soffit vent on the underside of the overhanging joists. 
  • Finished grade should slope well away from a pier foundation — about a slope of 4 in. in 10 ft.
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