Setting out a building foundation is one of the most important tasks on a construction site — and one of the most unforgiving. Get it wrong and everything that follows is off: walls out of alignment, columns shifted from their grid, drainage running the wrong way. It is also one of the things most often done poorly on small to medium sites where there is no licensed surveyor and the responsibility falls on the site engineer or supervisor.
This guide takes you through the full setting out process step by step — from understanding the setting out plan to establishing corner pegs, checking diagonals, and transferring levels to excavation.
Quick Answer: Setting out a building foundation involves transferring the building dimensions from the drawings onto the actual ground. The key steps are: establish a baseline from the site boundary, mark building corner positions, check diagonals for squareness, set profile boards outside the excavation zone, and transfer the formation and foundation levels using a dumpy level.
What Setting Out Actually Means on Site
Setting out is the process of transferring the dimensions and positions shown on the building drawings onto the actual ground. Before a single bucket of excavation begins, the site team must establish where every wall, column, and foundation element sits in relation to the site boundary and to each other.
The starting point is the setting out plan — also called the layout plan. This drawing shows the building footprint, the required setback distances from the boundary, the column grid with dimensions, and a reference benchmark. If you do not have a stamped setting out plan from the engineer or architect, stop work and get one before proceeding.
The truth is.. setting out from an architectural floor plan alone — without confirmed setback dimensions — is how buildings end up encroaching on road reserves or neighbouring plots. It happens more often than it should on self-build and small commercial sites across Kenya.
Equipment You Need for Setting Out a Building Foundation
The minimum equipment for accurate setting out on a residential or commercial project includes:
- 30m or 50m steel measuring tape — not a fabric tape, which stretches under tension
- Profile boards — horizontal timber boards set outside the excavation area to hold reference string lines throughout construction
- String lines and nails — for marking the building outline and wall centrelines
- Optical dumpy level or laser level — for establishing and transferring levels
- Levelling staff — read with the dumpy level for height differences
- Plumb bob — for transferring horizontal positions vertically into the excavation
- Theodolite or total station — for buildings over 20m in length or irregular in shape
For simple rectangular buildings under 20m, right angles can be established using the 3-4-5 method (or its multiples: 6-8-10, 9-12-15). For longer buildings, the small angular error in a hand-set 3-4-5 triangle accumulates and the building can end up noticeably out of square. Use a theodolite or at minimum verify with diagonal measurements.
The Step-by-Step Foundation Setting Out Process
Follow these five steps in sequence. Do not skip ahead to excavation before all steps are complete and checked.
Step 1 — Establish the baseline
The baseline is the reference line from which all other measurements start. It is usually set parallel to the front boundary or an existing road edge. Measure the required setback from the boundary as shown on the setting out plan and drive two pegs to define this line.
Step 2 — Mark the building corners
From the baseline, measure the building dimensions as shown on the drawing. Drive timber pegs at each building corner. Confirm you are working to the correct face — the drawing should specify whether dimensions are to the outer face of the wall, the inner face, or the centreline of the column grid.
Step 3 — Check diagonals
This is the most critical check in the entire setting out process. Measure both diagonals of the building footprint. For a rectangular building, both diagonals must be equal. The acceptable tolerance is ±5mm over a 20m diagonal. If the diagonals differ, adjust the corner pegs before moving forward. A building set out as a parallelogram will cause structural problems for its entire service life.
Step 4 — Set profile boards
Drive profile boards at each corner, positioned 1.5m to 2.0m outside the building lines so they stay clear of the excavation. Mark the foundation width, the wall or column centrelines, and the outer edge of the foundation on the board face using saw cuts or nails. These marks hold your reference positions throughout the excavation, blinding, and foundation construction phases.
Step 5 — Transfer levels
Set up the dumpy level on firm, stable ground with a clear sight line to the staff. Read the benchmark level from the drawings and establish the site datum. Mark the formation level (bottom of excavation) and the foundation soffit level on the profile boards using the staff and a level rod. These level marks must be checked by the site engineer — not assumed.
Common Setting Out Mistakes and How to Avoid Them
The most common error is confusing the dimension reference point. Using the outer face of a wall as the setting out position when the drawing shows the centreline of the column grid shifts everything by half a wall thickness. Always read the drawing notes before taking any measurements.
Dragging a tape over uneven ground introduces accumulated error across long measurements. Keep the tape horizontal and plumb down to the peg rather than following the slope of the ground. On sloping sites, a series of shorter horizontal measurements with plumb-bobs is more accurate than a single dragged tape.
Honestly.. the most expensive oversight on any site is not checking diagonals. It takes two minutes and two people. Not doing it has caused structural remediation work costing hundreds of thousands of shillings on buildings that were visibly out of square by the time the first-floor slab was cast.
Frequently Asked Questions
Q: What do you do if the site is not level?
Setting out is done in plan (horizontal position) first, then levels are transferred separately. Even on a sloping site, the horizontal positions of the building corners are established from a level instrument and horizontal tape measurements. Once corners are fixed, levels are marked on profile boards using the dumpy level. Never try to set out a sloping site by running a tape along the slope — always work horizontally.
Q: Can you set out a building without a theodolite?
Yes, for simple rectangular buildings under 20m. Use the 3-4-5 method to set right-angle corners, then verify with diagonal checks. For any building over 20m in length, on a sloping site, or with irregular geometry, a theodolite or total station is strongly recommended. Errors in manual right-angle setting accumulate over distance.
Q: What is the difference between a setting out plan and a floor plan?
A floor plan shows the internal layout — rooms, openings, finishes. A setting out plan shows the building position relative to the site boundary, the column or wall grid with exact dimensions, benchmark levels, and north point. The setting out plan is the document used to physically locate the structure on the ground. Always work from the setting out plan, not the floor plan.
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