Do I Need a Survey for Planning Permission?

The Short Answer

For most planning applications involving an existing building — an extension, conversion, change of use or alteration — yes, you will need a measured building survey. Planning authorities require accurate existing condition drawings as part of the application, and producing these to the required standard requires a professional survey.

There is no legal requirement to commission a professional survey specifically — but there is a requirement to submit accurate drawings, and for all but the simplest properties, a professional survey is the only reliable way to produce them.

What Drawings Does a Planning Application Require?

A standard householder planning application in England (for a house extension or alteration) typically requires:

• Existing floor plans — showing the layout of the building before any works, at 1:50 or 1:100 scale
• Proposed floor plans — showing the layout after the proposed works
• Existing elevations — drawings of the external faces of the building before works
• Proposed elevations — showing the external appearance after works
• Existing and proposed sections — where the works affect the building's cross section
• Site plan / block plan — showing the building in the context of its site and boundaries, at 1:500 scale
• Location plan — at 1:1250 scale, usually based on an Ordnance Survey map

The existing drawings are the starting point — your architect cannot produce the proposed drawings without knowing accurately what's there now.

Can My Architect Use the Original House Plans?

Possibly — but there are significant risks. Original plans from when a house was built may be decades old. In that time, the building may have had extensions added, walls moved, rooms converted or other alterations made that aren't reflected in the original drawings. If the existing drawings submitted with a planning application don't match the actual building, planning officers may notice during a site visit — which can cause delays or refusal.

For newer properties with no alterations, original plans may be usable. For any property that's been modified, extended or is more than about 20 years old, a fresh measured survey is strongly recommended.

What Happens If the Drawings Are Inaccurate?

If incorrect existing drawings are submitted as part of a planning application, several problems can arise:

• The planning authority may request amended drawings, delaying the application
• Proposed works designed from inaccurate existing drawings may not work on site — requiring redesign after planning approval
• Permitted development calculations (size limits for extensions relative to the original building) may be incorrect, invalidating the permission
• Building regulations drawings based on inaccurate surveys can create problems during construction

The cost of a professional survey is small relative to the total project cost — and it's far less than the cost of redesigning after inaccurate drawings have caused problems downstream.

When Might You Not Need a Survey?

There are situations where an existing survey may not be strictly necessary:

• New build on a clear site — if there is no existing building, there are no existing condition drawings required. You will still need a topographical survey of the site.
• Very simple single-storey extensions to straightforward modern houses where accurate original plans are available
• Some prior approval applications — certain permitted development applications require minimal supporting drawings

Even in these cases, a professional survey provides peace of mind that the drawings are accurate. Your architect is best placed to advise whether a survey is necessary for your specific application type.

What About Listed Buildings and Conservation Areas?

For listed building consent applications and works in conservation areas, a measured survey is particularly important. Listed building applications are scrutinised carefully and often involve detailed assessment of how proposed works relate to the existing building fabric. Accurate existing drawings — often at a higher level of detail than for standard applications — are usually required.

Laser scanning is particularly well suited to listed buildings as it captures complex and irregular historic building geometry with far greater accuracy than manual measurement.