Every wood-framed wall is tied to its foundation by sill plate anchor bolts, and the spacing rules are prescriptive in the IRC. This tool turns a wall length into a complete bolt layout: how many bolts, how far apart, where each one lands from the corner, and how deep to embed them.
How it works
The layout fixes a bolt the end distance in from each corner, then evenly divides what is left so no space exceeds the code maximum:
end bolts = end_distance from each corner (max 12 in)
interior = wall_length - 2 * end_distance
spaces = ceil(interior / max_spacing) (max_spacing 6 ft)
bolt count = spaces + 1 (minimum 2)
spacing = interior / spaces
positions = end_distance + i * spacing, i = 0 to spacesEmbedment defaults to the 7-inch IRC minimum, rising to 15 inches when a braced or shear wall bears on the sill. Short walls fall back to the two-bolt minimum.
Why the end distance rule matters
A bolt within 12 inches of each plate end is not just a formality. The plate end is the point most vulnerable to uplift and sliding — without a bolt there, the free end can lift off the foundation under wind or seismic forces even while the rest of the plate stays anchored. The IRC requires this end bolt precisely because experience shows that unrestrained ends are how wood-framed walls begin to peel away from foundations in storm and earthquake events.
Worked example
A 24-foot exterior wall with a 6-inch end distance and 5-foot max spacing:
- Interior span:
24 ft - 2 * 0.5 ft = 23 ft - Spaces needed:
ceil(23 / 5) = 5 - Bolt count:
5 + 1 = 6 bolts - Even spacing:
23 / 5 = 4.6 ftbetween interior bolts - Positions from corner:
0.5 ft, 5.1 ft, 9.7 ft, 14.3 ft, 18.9 ft, 23.5 ft
Each position is within the 6-foot maximum and within 12 inches of each end.
Shear walls and higher-load situations
The 7-inch embedment depth is the prescriptive minimum for standard cases. When a shear wall panel bears on the sill, the uplift and shear forces transmitted to each bolt are substantially higher. IRC braced wall provisions increase the minimum embedment to 15 inches for anchor bolts serving shear walls, and often require 3-inch square plate washers to prevent cross-grain crushing of the sill plate.
In Seismic Design Categories D and above, or in high-wind zones (ASCE 7 wind speed areas), engineered designs typically call for:
- Closer bolt spacing (often 4 feet or less)
- Larger bolt diameters (5/8 inch rather than 1/2 inch)
- Hold-down hardware at wall ends in addition to anchor bolts
- Code-compliant plate washers
Always check your local jurisdiction’s amendments to the IRC, since many coastal and seismic regions have adopted more stringent requirements than the base code provides.
Tips and notes
- The 6-foot maximum is a ceiling, not a target — use closer spacing whenever load requirements or good practice suggests it.
- Mark bolt positions on the sill plate before placing it on the foundation so the drilling template is accurate.
- Confirm bolt positions do not land in a window or door rough opening, where the sill is interrupted.
- Use this tool as a planning aid; the structural engineer of record or building department governs actual requirements for your project.