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Extensions

Side return and wraparound extension estimate.

Side return and wraparound extensions are popular for terraced and semi-detached houses in urban areas. Tight access, party walls, and restricted plant space make these projects distinct — and easy to underprice.

Authored by Alexandr Vreme & Maksym Vasylkov
Published July 2026 — Next review July 2027

Who this guide is for

For builders estimating side return, infill, or full wraparound extensions on terraced and semi-detached houses in urban settings. These projects sit tight against boundaries and demand careful handling of access and party wall regulations.

What makes these projects different

• Narrow access — the side return is often under 2 m wide, restricting plant and material movement
• Party walls on one or both sides — full party wall procedure required
• Restricted plant access — mini-diggers only for excavation; hand-digging in tight spots
• Neighbour notification requirements — party wall notices and possible temporary access for scaffolding

Information you need before pricing

• Existing boundary wall construction — solid brick, cavity, or masonry
• Party wall surveyor appointment — already appointed, or needs arranging?
• Access route — how will materials, skips, and plant reach the work area?
• Gas and electric meter locations — may need temporary disconnection or relocation

Typical scope of works

• Strip and dig — hand-dig or mini-digger within the tight access
• Tanking against adjoining walls — waterproofing where the new build meets existing boundaries
• Steel beam to open the side return into the existing kitchen or living space
• Glazed roof or roof lantern — the most popular choice for side returns
• Full-height glazing to the opening end for maximum light

Commonly missed costs

• Party wall awards — typically £1,000–£2,500 per neighbour for the surveyor’s fees and award preparation
• Restricted access labour premiums — hand-digging and double-handling materials add time
• Making good neighbour’s decorations after party wall works on the shared wall
• Temporary accommodation for the client during the most disruptive phases
• Scaffolding on the neighbour’s property — may require access fees or compensation

Miniature worked example

A 4 m × 2.5 m side return extension with a roof lantern:

• Substructure (hand-dig, foundations, slab, tanking): £6,000
• Shell (cavity walls, steel beam, roof lantern): £22,000
• Glazing (full-height window to opening end): £8,000
• Finishes (plaster, tiling, flooring, decoration): £10,000
• Preliminaries (scaffold, skip, welfare, party wall award): £6,000

Total: approximately £52,000. A full wraparound (side return plus rear extension) on the same property would be in the region of £95,000, depending on width and specification.

Suitable output documents

• Detailed estimate with separate preliminaries and party wall costs
• Priced bill of quantities itemising restricted-access work
• Schedule of works showing dependencies on party wall awards

Questions to ask before pricing

• Is party wall consent already served, or does it need to be arranged?
• What is the access width — can a mini-digger fit, or is hand-digging needed?
• Where are the gas and electric meters, and will they need moving?
• Is scaffolding allowed on the neighbour’s property?