At a glance
| Measure | How | Tool | Record |
|---|---|---|---|
| Datum | One datum line and level, a stated height above finished floor, marked on the walls | Laser level, tape | Datum height, who set it, date |
| Floor level | Readings on a grid and at each wall, against the datum | Laser or water level, straight edge | Height at each point; highest and lowest |
| Ceiling height | At several points along each wall: at least both ends and the middle | Laser distance meter, tape | Each height; the lowest |
| Wall plumb | Offset from a plumb line at top, middle and base, in both directions | Plumb line, laser, long level | Offset at each height |
| Wall flatness | A straight edge held on the wall at several heights and directions | Straight edge, tape | Gap and where it is |
| Squareness | Both diagonals of the plan, corner to corner. Equal diagonals mean square corners | Tape, laser distance meter | Diagonals A and B; the difference |
| Openings | Width and height at several points, reveal depth and finish | Tape | The smallest of each |
| Services | Sockets, pipework, vents, sprinklers and anything that must pass through the work | Tape, photographs | Position from the datum and from a wall |
| Fixings and surfaces | What the work fixes to (backing, studs, masonry) and whether the walls and floors are finished | Inspection, the contractor's records | Positions; state and date |
No tolerance figure is given here: each comes from the specification, the contract or the maker's statement.
Survey the building as it is, when it is ready
A drawing is design intent. It shows a wall as a straight line, a floor as flat and a corner as a right angle, and in a real building none of them is. Joinery made to the drawing alone meets the building with gaps that have to be hidden or fixed. Joinery made to a verified survey meets it with an allowance chosen in advance.
Survey when the surfaces you will fix to or fit against are finished: plaster or board on the walls, screed or finished floor, ceiling in place. A survey taken before the plaster goes on measures a surface that will not exist. If the survey has to be early, mark every dimension that depends on an unfinished surface as provisional, agree when it will be verified again, and make the re-verification a condition of release. In our process, site dimensions are verified before production commits, and surveys are reconciled with the drawings (see design development). The access measurements for the same visit are on the delivery access survey sheet.
One datum, readings against it, and a scribe that covers the worst case
A datum is a single reference line and level, set once at a stated height above finished floor level and marked on the walls, so that the designer, the contractor and the maker all mean the same height when they write a dimension. Every reading is taken to it.
For a wall, take three plumb readings, at the top, the middle and the base, and write down the offsets rather than a pass or fail. A flat wall that leans is a different problem from a wall that bows, and the offsets show which. Then check the plan: measure both diagonals of the room, corner to corner. If they are equal the corners are square; the difference tells you how far out the room is.
Joinery that meets a wall, floor or ceiling is made with a scribe: a deliberately generous strip that is trimmed on site to follow the actual surface. The allowance has to be built in when the work is made, because it cannot be added afterwards. It must cover the largest gap you recorded and still leave material to trim. The survey tells the maker how much is needed, and the maker states how much is built in. Where the two disagree, you find out before manufacture, not on the day of fitting.
Who measures what
Disputes about dimensions are usually disputes about who was meant to measure. Settle it in writing before the survey. A working division looks like this:
| Party | Measures or provides | Signs off |
|---|---|---|
| Designer or architect | The design-intent dimensions, the setting-out grid and the datum definitions; which edges are fixed and which may be scribed; the finished floor level. | The drawing the maker works to, and which dimensions may move. |
| Main contractor | The built condition: openings, structure, services positions and the datum on site. Confirms the surfaces are complete and ready to be measured, and gives access. | Written confirmation that the areas are ready and that the readings supplied are current. |
| Maker, through the studio | A survey of the readied areas against the datum, or a check of the contractor's readings. The scribe and tolerance allowances, shown on the shop drawings. | Shop drawings with each dimension marked verified or from the drawings, and a request for release for manufacture. |
| The studio | Coordinates the survey between designer, contractor and partner workshop, and reconciles it with the drawings before production commits. | Issues the survey record for sign-off. |
| Client's surveyor, if appointed | A measured survey of an existing building, with a stated accuracy. | The measured drawings and the accuracy they state. |
The contract decides who carries which risk. This table is a working division, not a contract term: have the allocation written into your specification or subcontract.
Tolerances: where the numbers come from
This sheet gives no tolerance figures for walls, floors or joinery, and that is deliberate. A figure copied from a general source can contradict the document that governs the job. Use the figure from the first of these that exists: the project specification and contract, then the maker's own tolerance statement, then any published standard the specification calls up. Standards that are commonly named are listed below; we have read none of their figures, so confirm the current edition before you rely on one.
Keep three kinds of tolerance apart, because they belong to different people:
| Kind of tolerance | Set by | The question to ask |
|---|---|---|
| Building (structure, plaster, floors, ceilings) | The contract and the main contractor | How far out of plumb, level or flat may the surface I will fix to be, and where is that written? |
| Manufacture (the joinery as made) | The maker's own tolerance statement | What do you build to, and what do you need from the building in return? |
| Fit (joinery to the building) | The shop drawing: scribe allowances, gaps and shadow gaps | What allowance is built in, and what gap or reveal is left when the work is fitted? |
Sign-off: from survey to release for manufacture
A survey only protects you if it ends in a decision someone signed. The sequence below is a working convention, not a published procedure. Keep it short enough that it is actually followed:
- Survey when the surfaces are ready, against the agreed datum.
- Record readings, not opinions: the offset at each height, the heights, the diagonals, with date, tool and name.
- Reconcile with the drawings. List every difference and say who decides what changes.
- Mark each dimension on the shop drawing: V where it has been verified on site, D where it is taken from the drawings and has not been verified, S where a scribe allowance applies.
- Approve. The designer approves the shop drawing; the contractor confirms the site readings are current.
- Release in writing, naming the drawing revision and the survey record it relies on.
- Re-verify after any change to the building before the affected parts are made, and record the change as a variation.
A record can be a simple table. Placeholders in square brackets show what each cell holds:
| Location | Item | Reading | Taken to | Tool | By, date |
|---|---|---|---|---|---|
| [Wall A, bay 2] | [Plumb] | [Top, middle, base: offsets] | [Datum line, 1 m above FFL] | [Laser] | [Name, date] |
| [Wall A] | [Ceiling height] | [Left, centre, right] | [Finished floor level] | [Distance meter] | [Name, date] |
| [Room 3] | [Diagonals] | [A and B] | [Corner datum point] | [Tape] | [Name, date] |
NBS notes that suppliers' shop drawings are often not issued back to the design team for comment (2020), which is why a written release matters. Who holds design responsibility for a detail depends on whether the specification is prescriptive or descriptive: see the joinery specification checklist and why bespoke quotes differ.
Specification wording
Paste into your schedule or specification and replace anything in [square brackets] with your own figures. Wording is a starting point: your specification governs.
All dimensions that affect [items] are to be verified on site by [Contractor / maker / designer] before the shop drawings are approved. Contract drawing dimensions are design intent. Where a verified dimension differs from the drawing by more than [ ] mm, [name] is to be told in writing before manufacture.
The datum is [description] at [ ] mm above finished floor level, marked on [walls] by [Contractor] on [date]. The survey is taken to this datum after [plaster / boards / floor screed] are complete and dry. The record gives plumb readings at [top, middle and base], flatness, heights and diagonals, with the date, tool and name of the person who took them.
[Maker / Contractor] carries the risk of dimensions it has verified and signed on the shop drawing. Dimensions marked D (taken from the drawings) remain the risk of [Contractor / designer] until verified. Dimensions changed on site after release for manufacture are variations.
Joinery abutting walls, floors or ceilings includes a scribe of [ ] mm, or as the shop drawing states, cut to the finished surface on site. If the surveyed gap is greater, the maker is to tell [name] before manufacture.
Manufacture of [item] is released on a written instruction from [designer] that names shop drawing [number, revision] and the survey record dated [date]. No part is released on a drawing dimension marked D unless the instruction says so.
Terms used on this page
- Scribe
- To shape the edge of a panel or board so it follows an uneven wall, floor or ceiling; a scribe strip is a deliberately oversized piece cut to fit.
- Tolerance
- The permitted difference between a stated dimension or position and what is actually achieved, such as length, flatness, plumb or gap width. Manufacturing and on-site installation tolerances are different and should be specified separately.
- Shop drawings
- The maker's detailed drawings of how an item will be built, with dimensions, materials, fixings and finishes, for the designer to check before manufacture.
- Datum
- A single reference line and level, usually a stated height above finished floor level, marked on the walls and used by everyone as the basis for dimensions and readings.
Standards and sources
- BS 8000-0:2014+A1:2024 Workmanship on construction sites: general principles: named only; text not read. Confirm edition and status.
- BS 5606:2022 Accuracy and tolerance in design and construction: guide: named only; text not read.
- ISO 7976-1:1989 Tolerances for building: methods of measurement, methods and instruments: named only; text not read.
- NBS: RIBA Plan of Work 2020 and specification: shop drawings and design responsibility (17 Jun 2020, read 5 Nov 2026).
- Make Bespoke Studio: Design development: how site surveys are reconciled with drawings.
Questions we are asked
Who should measure for bespoke joinery?
Someone named in the specification, taking readings to an agreed datum once the surfaces are ready. It may be the contractor, the maker or the designer. What matters is that the person is named, the readings are recorded, and the maker works from the record.
Can I use the architect's drawings instead of surveying?
Drawings show design intent, not the finished building. Walls are rarely plumb, floors rarely flat and corners rarely square, so joinery made to the drawing alone has to be adjusted on site. A survey lets the allowance be chosen before manufacture.
How much scribe allowance should I build in?
The figure comes from the survey and from the maker: it must cover the largest gap you record and still leave material to trim. We do not give a single number, because it depends on the piece, the wall and the finish. Ask the maker what is built in and compare it with your readings.
How do I check that a room is square?
Measure both diagonals of the plan, corner to corner, with the same tool at the same height. If they are equal, the corners are square, and the difference shows how far out the room is. For one corner, measure 300 mm along one wall and 400 mm along the other: the distance between the marks should be 500 mm.
What if the walls are not finished when I need to survey?
Survey provisionally, mark every dimension that depends on an unfinished surface as taken from the drawings, allow for the thickness the finish will add, and agree when it will be verified again, before the release for manufacture.
What is a datum?
A single reference line and level, usually a stated height above finished floor level, marked on the walls. Every reading and every dimension is taken to it so that everyone means the same height.
Download the factsheet
A two-page A4 PDF with the survey checklist, the plumb, scribe and diagonal sketches, the who-measures table and sign-off wording, to keep with your project file.