What is a measured survey, and why does a design start from one?

What a measured building survey records

RICS publishes the standard specification, Measured surveys of land, buildings and utilities (3rd edition, reissued as an RICS professional standard in December 2023). Section 4 lists what a measured building survey records. Some items are ticked by default; others are recorded only when the client selects them.

The standard draws a distinction worth using when you brief a surveyor. A height is a dimension measured from the floor, such as a ceiling height. A level is a value related to an agreed datum, such as a floor level. Levels let the survey tie the house to the garden, the street and the neighbours.

Accuracy is specified by band. The RICS example is that a client wanting plan accuracy of 10 mm at a 95% confidence level should select band C (paragraph 2.3.2). Tighter bands take more work and may cost more.

Laser and point cloud surveys

A laser scanner records the position of a very large number of points on every surface it can see. Scans from several positions are joined, or registered, into one point cloud. RICS treats the point cloud and the CAD drawings as separate deliverables (section 8), so a point cloud on its own is not a set of drawings. If you want both, ask for both, and ask what software and file format each will come in.

A point cloud is most useful where the geometry is irregular: an old house with walls out of square, a roof with several pitches, or a basement where every millimetre of headroom counts.

Why a design starts from one

• The planning application. Plans and drawings must be drawn to an identified scale (Planning practice guidance, paragraph 023, under article 7 of the Development Management Procedure Order 2015). The existing drawings are the base for the proposed ones.
• Permitted development. The limits in the General Permitted Development Order are set in metres from the original house and from ground level. A survey that is out by a few hundred millimetres can put a scheme on the wrong side of a limit. See the original house.
• The structure. Beam spans, bearings and floor-to-ceiling heights for a loft conversion come from the survey.
• The price. Every builder prices from the same drawings. If they are wrong, the error shows up as a variation once work starts.

A survey does not fix your boundary

A measured survey records the walls and fences on the ground. It does not establish where the legal boundary is. Under section 60 of the Land Registration Act 2002, the boundary shown on a registered title is a general boundary unless it has been determined under that section, and a general boundary does not determine the exact line. If the design runs close to the boundary, the survey shows where things are; the title and, if needed, the neighbour's agreement settle where the line is.

What to ask for

• Extent. Every floor, the loft, the garden, and the neighbours' walls, windows and extensions near the works, which matter for planning and party wall purposes.
• Levels. Floor levels in each room and external ground levels, related to a stated datum.
• The roof. A roof plan with ridge and eaves levels, and the roof structure if you are converting the loft.
• Sections through the stair and through each part of the house being altered.
• Elevations of every face the work touches.
• Formats. The CAD file format and version, a PDF set, and any point cloud, with the accuracy band stated.
• Drainage. Inspection chambers come with cover levels only. Depths and pipe runs need a separate drainage survey.

What it costs

Checkatrade's cost table (updated May 2024) puts a measured building survey at £800 to £2,000, with an average of £1,400. That is a national published figure, not a quote. Ask each surveyor for the site time and the delivery date; no published source gave a reliable typical timescale for a domestic survey.