How to Lay Out a Foundation with Batter Boards and String
Batter boards are simple horizontal boards set on stakes a few feet outside each corner of a planned foundation. They hold string lines that mark the outside of the foundation, and because they sit outside the dig area, the layout survives excavation. When the hole is dug you can re-attach the strings and find every corner again.
What you need
- 2×4 stakes and 1×6 or 2×4 cross boards (about 4 ft long)
- Mason's line (nylon string), a 100 ft tape, a line level or laser
- Nails or screws, a sledge, marking paint, and a helper
1. Rough out the corners
Using the site plan and setbacks, drive a temporary stake at each foundation corner. Measure from a fixed reference — a property line, an existing wall or survey pins — not from guesswork. Confirm the rough rectangle matches the plan dimensions.
2. Build the batter boards
About 4–6 ft outside each corner, set an L-shaped pair of batter boards: three stakes with two cross boards, one parallel to each foundation wall. Set all cross boards at the same height using a level, a water level or a laser. That common height becomes your reference for excavation depth and for the top of the forms.
3. Pull the first line
Stretch a string between two batter boards along the most important side — usually the side that must be parallel to a street or property line. Position it directly over the corner stakes and tie it off tight. This is your reference line; do not move it again.
4. Square the second line with 3-4-5
Attach the second string at the corner and run it to the opposite batter board. Where the strings cross is the corner. Measure along the first string 12 ft and mark it with tape; measure 16 ft along the second string and mark it. Slide the second string along its batter board until the diagonal between marks is exactly 20 ft. Use the largest multiple the layout allows — see the squaring calculator for any size.
5. Set the remaining lines
Measure the foundation length and width from the corner along each string and set the other two strings parallel. Repeat the 3-4-5 check at each corner.
6. Check the diagonals
Measure corner to corner both ways at the string intersections. For a 24 × 36 ft foundation, each should read √(24² + 36²) = 43.27 ft (43' 3-1/4"). Adjust strings along the batter boards until both diagonals match within about 1/4". The diagonal check calculator shows how far off you are and which way to move.
7. Mark and dig
Saw-kerf or nail the cross boards where each string sits, so the strings can be removed and replaced exactly. Drop a plumb bob from each intersection, mark the ground, and paint the dig lines (usually with extra width for forms and working room). Remove the strings for excavation, then re-attach them to set the forms.
Common mistakes
- Setting batter boards too close — the excavator knocks them out.
- Strings that sag over long runs. Pull them tight and support long lines.
- Squaring from a reference line that is not actually parallel to the property line.
- Not marking string positions before removing them.
Watch
Questions
How far from the corner should batter boards be?
Typically 4 to 6 feet outside the foundation line, far enough that excavation and equipment will not disturb them.
Do batter boards need to be level?
Yes. Setting them all at the same elevation turns the strings into a level reference for excavation depth and form height.