How to Read Footing Plans: A Field Guide for Concrete Contractors

A footing plan looks like a maze the first time you open one, but every residential foundation plan is built from the same handful of conventions. Learn them and you can pull the numbers off any wall company drawing in the trade — the same conventions show up whether the plan came from a St. Catharines bungalow designer or a custom builder three provinces over.

This is a field guide for reading the plan, not designing the foundation. The goal is a clean takeoff: total linear feet of footing and a pad count you can stand behind.

Where do the footings live in a permit set?

A full permit set has a dozen or more sheets. The footings live on the foundation plan — look in the sheet index for a page labeled S1, A1, A0.1, or spelled out as “Foundation Plan” or “Basement Plan.” On a small residential job the whole foundation might be one sheet.

Do not expect footings to be drawn as their own bold lines. In plan view you are usually looking at the foundation walls; the footing under each wall is either invisible or shown as a light dashed line offset a few inches outside the wall. The footing follows the wall, so the wall layout is the footing layout. The footing’s actual size — width and thickness — comes from a section detail elsewhere on the sheet, not from the plan view.

Read the title block and confirm the scale

Before measuring a single dimension, read the title block in the corner. It gives you three things that make or break the takeoff:

• Scale. Residential foundation plans are usually drawn at 1/4” = 1’-0”, but never assume — the title block states it. If you ever have to scale a dimension off the paper (you should rarely need to), a wrong scale multiplies every measured length.
• Sheet number and revision. Confirm you are on the foundation sheet and note the revision (more on that below).
• Project address. Match it to the job so you are not measuring the wrong plan. Wall companies routinely send lookalike bungalow plans that differ by a few feet.

Decode the dimension strings: the classic out-to-out vs. inner-face mismatch

This is the single most misread thing on a residential foundation plan, and it trips up new estimators every time.

Exterior dimension strings run to the outside face of the foundation wall — “out-to-out.” The chain of numbers wrapping the perimeter is measured to the outer skin of the concrete, which is exactly what you want for a perimeter takeoff. Add that chain and you have the outer run with no scaling.

Interior dimension chains typically run between the inside faces of walls. So when an interior string will not close against the perimeter numbers, the wall thickness is almost always the gap — not a drafting error. On a plan with 10-inch walls, an interior chain measured inner-face-to-inner-face is 10 inches short of the out-to-out envelope on each affected wall.

Two habits keep the strings honest:

• Opposite sides must agree. On a roughly rectangular plan, the segments along the north side sum to the same total as the south side. If they don’t, you misread a number — find it before you pour, not after.
• Jogs count twice. Every bump-out or step in the perimeter adds two short runs, in and out. Those 2- and 3-footers are what get missed at 11 p.m.

Wall schedule and thickness call-outs

Somewhere on the sheet — as a table or as call-outs on the walls themselves — is the wall schedule telling you which lines are concrete foundation walls and how thick each is. This is what separates your scope from everyone else’s.

• 10 inches is common for full basement foundation walls.
• 8 inches shows up on porch walls, cold rooms, and garage grade walls.
• Wood-frame load-bearing walls are a different animal — sometimes carried on a shallow interior strip footing (for example 16” × 6”), sometimes not your scope at all. Identify them and apply your billing convention consistently.

If the plan uses double lines with a thickness dimension between them, that is a concrete wall. A single line is often a wood-frame wall. When in doubt, the schedule wins.

Section details: reading a 20”x6” footing under a 10” wall

The plan view tells you where and how long; the section detail (a cut-through of the wall, usually keyed with a bubble like 1/S2) tells you how big the footing is. A typical residential call-out reads something like a 20” × 6” footing under a 10” wall — that is a footing 20 inches wide and 6 inches thick, sitting under a 10-inch-thick foundation wall. The 2021 IRC sets the floor at 12 inches wide and 6 inches thick for footings (R403.1.1); the Ontario Building Code requires footing thickness of at least 100 mm (about 4 inches) and no less than the footing’s projection.

For a linear-foot takeoff, the footing width and thickness don’t change your length — they set the concrete volume and tell you which section a given wall follows. You still bill the run by its length along the plan.

Pad schedules

Interior support pads (pier pads) carry the posts under the main beam. On the plan they show up as small squares along the beam line, often dashed, and frequently keyed to a pad schedule that lists each pad’s size and depth. Residential interior pads commonly run from about 38” × 38” up to 46” × 46”, though 24”×24” pads 8–12 inches deep are common under a single basement telepost. Count them as units — never as linear feet — and note any size call-outs. If the plan shows posts on the beam line but no pads drawn, flag it; don’t guess a count silently.

Handwritten margin notes are ground truth

Wall companies write the numbers that matter in the margins by hand: the job address, total linear feet, pad count, rebar note, concrete cubic meters. These are their own figures for their own billing, which makes them the closest thing to ground truth you will get. Read them first, before you measure, then reconcile your independent takeoff against them. Agreement within a couple of feet is normal rounding; a 20-foot gap means a run got missed on one side. Zoom into every margin — a rebar note scribbled sideways next to the title block changes your rate.

Revision blocks and the stale-revision trap

Every sheet carries a revision block — a small table of revision numbers, dates, and short descriptions, usually stacked near the title block. The highest revision number is the current one.

The trap is measuring an old version. Foundations get revised: a wall moves, a wing gets added, a cold room shrinks. If you take off Rev A while the crew is pouring Rev C, your entire quantity is wrong and the error is invisible in your total. Two checks close the trap:

• Confirm the sheet is stamped or noted “Issued for Construction” (or the permitted set), not a preliminary or “for review” print.
• If you were sent a fresh copy, compare its revision block to the one you last took off. A bumped revision means re-measure the affected area — don’t assume the change was cosmetic.

Putting it together

Reading a footing plan is a fixed sequence: find the foundation sheet, confirm scale and revision, read the wall schedule to fix your scope, add the exterior string out-to-out, add interior runs between inner faces, pull footing sizes from the section details, count the pads off the schedule, and reconcile everything against the handwritten margin totals. Do that in order and the plan stops being a maze.

When you’re ready to turn that reading into a priced quantity, the concrete footing takeoff guide walks through the measuring and reconciliation step by step. FootingTakeoff does the same reading automatically and returns the runs drawn on your plan so you can check them against the margin notes in seconds.