Construction guide

Concrete piers and anchor bolts

A cast-in-place pier is the same basic build whether it carries a low deck, a raised deck, a pergola or a pavilion post: dig below the frost line, form it, pour it, and set the anchors before the concrete sets.

Updated October 2026

Structural work — verify locally

Pier depth, diameter, rebar, anchor type and permit thresholds come from your local building code and the connector manufacturer. These steps describe the common method; they do not replace a stamped plan or a qualified professional.

1. Size and locate the pier

Confirm the pier centers, spacing and diameter on the plan. Deck piers are commonly 10–12 in in diameter and sized by the load and soil.
The bottom of every pier must sit below the local frost line. In cold climates that can be 36–48 in; use your local number, not a rule of thumb.
Call 811 before digging. Keep piers clear of the house footing, drainage, utilities and major roots.
For a low platform, keep the pier top at or just above grade. For a raised structure, set it at the height the beam or post base needs.

2. Dig and form

Dig a straight hole to the required depth. Keep it clean, dry and free of loose soil; a slightly widened base helps uplift resistance.
Add 4–6 in of compacted clean gravel at the bottom of the hole.
Set a cardboard or wooden form plumb and brace it on two axes; extend it 1–2 in above grade for a low platform.
If the plan calls for rebar, tie the cage with about 3 in of cover. Do not add rebar without the plan.
Recheck spacing, depth and top height before any concrete goes in.

3. Mix and pour

Use a structural concrete mix — often 4000 psi; follow the bag or ready-mix ticket.
Mix to a workable, not soupy, consistency. Extra water lowers strength.
Pour in 6–12 in lifts and consolidate each lift with a rod or vibrator, working around the form and anchor locations.
Fill to the top, tap the form to release trapped air, and avoid cold joints by pouring continuously.

4. Set the anchors and post base

Use the anchor or post base the connector manufacturer specifies. Do not substitute rebar or unrated threaded rod.
Make a template board with the post-base hole pattern and bolt the base or anchors through it.
Lower the anchors into the wet concrete to the specified embedment. Keep the template supported, level and correctly oriented.
Check spacing, diagonal, plumb, edge distance and embedment before the concrete sets.
Protect the threads and do not bend the anchors after the concrete sets.
If drilling after cure: use the specified wedge or epoxy anchor, clean the hole, and torque to the manufacturer's value.
A post base holds a vertical post. When a beam sits directly on a pier, use a beam saddle with a flat base plate and side straps — never seat a horizontal beam in a post collar.

5. Crown, cure and load

Trowel the pier top with a slight slope away from the post base so water runs off.
Keep the concrete damp and covered for 24–48 hours; protect it from freezing and hot sun.
Remove forms carefully after the initial set; do not disturb the anchors.
Do not load the pier for about 7 days. Full design strength is at about 28 days.

6. Inspect before you build

Every pier below the frost line; diameter and spacing match the plan.
Pier tops level and at the required height; no honeycomb, voids or exposed rebar.
Anchors plumb, correctly spaced, at the required embedment and edge distance; threads clean.
Post base level, standoff gap intact and drain hole clear.
Gravel sits in the hole under the concrete; permeable fabric goes around the pier after cure — never under the concrete, never plastic sheeting.
Schedule the local inspection if the permit requires one.

Sources

International Code Council — International Residential Code (IRC) — Model code for guards, stairs and footings; your local amendments govern.
Concrete Masonry & Hardscapes Association (formerly ICPI) — paver installation guidance — Industry guidance for paver base, bedding and edge restraint.

Always follow the local building department and the connector manufacturer; the steps above are the common method, not a site-specific design.

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