A measured survey records the existing house and the parts of the site that matter to your proposed extension. The designer uses those measurements to draw the property as it stands and test how the new work would fit. For a home in England, the survey can also provide the base information for the existing plans and elevations used in a planning application.
Agree What the Survey Needs to Capture
For a rear extension, the designer may need the dimensions and layout of the affected rooms, positions of doors and windows, and the relationship between the rear wall, garden and adjoining parts of the house. Floor and ground levels can matter where there is a step between inside and outside or the garden slopes. The scope should follow the proposal. A side extension may require a closer look at the side passage, whereas a two storey proposal may need more detail about the upper floor and roof.
Ask what the survey will produce and which areas it will cover. The RICS measured survey standard explains why survey specifications and deliverables should be agreed for the intended use. If the designer needs detailed site levels, specialist drainage information or evidence of a legal boundary, discuss that separately. Visible fences and walls can be recorded as physical features. Their position alone does not establish the legal boundary.
Get the Property and Information Ready
- Share your address, the type of extension and a rough sketch or marked-up photograph.
- Send any existing drawings and mention alterations that took place after they were prepared.
- Arrange access to the rooms, garden and passages the designer needs to measure.
- Flag known access issues, a steep change in level or areas obscured by fixed fittings.
Ask how the team will handle inaccessible or concealed elements. A survey can record accessible information and identify where a separate investigation may be needed before detailed design. Old estate agent plans can help explain your brief, but the team should decide which dimensions need checking before relying on them.
Example: A Rear Extension on a Sloping Plot
A homeowner sends a floor plan that shows the rear door and the garden outline. At the survey, the designer records a step at the back door and a fall towards the boundary. This gives the team a basis for testing floor levels and deciding whether an additional site survey is needed. They can draw the relationship between the proposed extension and the garden, then discuss any change to steps or access before fixing the design.
Ashbridge includes a measured survey in its planning stage. The arrangement can vary by location. If you have a sketch and property address, ask what the extension design survey would cover.