Precast Piers

Although simple to install, these piers (see below) are heavy and awkward to move and set into position. To level their footings, drive stakes into the footing holes, mark stakes with a water level as you would for concrete forms, pour concrete up to the marks, and remove the stakes before the concrete begins to harden. Because they generally come no more than 18 inches high, they are used mainly on level sites that have a shallow frost line.

Locate and dig the footing-and-pier holes as for a pole platform, excavating each hole 16 inches wide to the required depth.

At the center of each hole, drive a length of 1/2 inch rebar into the ground until the top of the rod is about 6 inches lower than the planned height of the pier above ground (right).

Fill the first 8 inches of the holes with concrete, creating footings. Allow the concrete to cure for at least one day.

Mark the planned height of the piers on a corner form.

Have a helper hold one end of a water level or a transparent hose filled almost completely with water at the height of the mark on the corner form.

Hold the other end against the next form in the row (above) and mark a line at the level of the water.

Repeat the process to mark each form.

Cut the forms at the marked heights with a hacksaw.

With a helper and a string, go from form to form to align and mark the position of a beam anchor on the front and back of each form, ensuring that each beam—3 inches wide for doubled 2-by-10s or 2-by-12s, or 4 1/2 inches for a triple beam—will be centered on the pier.

Mix enough concrete to fill the forms, then shovel it into each form in the row, using a length of rebar to pack the concrete down with every foot you add.

As you fill each form, level the concrete off with the top of the form using a 2-by-4, then following the marks on the form, push an anchor that is as long as the width of the beams to be installed (Step 5) into the concrete down to the embedment line marked on it. Embed anchors in concrete in the remaining forms in the same way.

Double-check the alignment of the anchors with the string, adjusting them to line up as needed.

Allow the concrete to cure for five to seven days.

Make a beam for each row of piers: For a prefab cabin, nail pairs of 2-by-10s or 2-by-12s together with 3-inch galvanized common nails. Drive three nails in a row about 1 inch from each end and stagger nails along both edges at 10-inch intervals. For an A-frame, make triple beams.

For a vapor barrier, set asphalt shingles on the piers, or cut 6-mil polyethylene sheeting into pieces to wrap around the bottom of the beam at each pier, and staple the pieces to the beam.

Set the beam into its anchor, then check whether it is level. If not, shim the low end by placing galvanized washers between the beam and pier.

Fasten the beam to each anchor by nailing into each hole (above).

Fasten joists to the beams as for a pole foundation (Step 8), then lay a subfloor across the joists.

Block and Precast Piers

Concrete-Block Piers

Cast a footing for each pier as for concrete piers (Step 1), but level the footings by marking the rebars with a water level as for concrete forms.

To keep the heights of the piers consistent, make a story pole: On a piece of lumber, mark lines at intervals equal to the height of a block plus a 3/8-inch mortar joint.

Trowel a bed of mortar on the footing and lay a concrete block on the mortar, centering the block around the rebar.

Add blocks and mortar to build up the pier, checking each course for level and plumb with a carpenter’s level (right), and for height with the story pole. Build each remaining pier in the same way, running a string between adjacent piers to keep them all consistent and in alignment.

Fill the cores of the piers with grout—concrete thinned with water so it can be poured—then embed concrete anchors in the piers and attach beams as for concrete piers (Steps 4 and 5).

Precast-Concrete Piers

Cast a footing for each pier as for concrete piers (Step 1), but proceed immediately, before the concrete cures.

With a helper, press a precast pier into the wet concrete (left).

With a carpenter’s level, ensure that the pier is level.

Position each remaining pier in the same way, running a string between adjacent ones to keep them aligned and level.

Install vapor barriers and attach beams to the piers’ built-in anchors as you would for concrete piers (Step 5), nailing exterior-grade plywood spacers at 24-inch intervals between the boards making up the beam, if necessary, to ensure the beam sits snugly in the anchors.