House Extension Cost in Cardiff: 2026 Price Guide

• Side return infill: £16,500-£27,500
• Single-storey rear extension: £23,500-£51,000
• Double-storey extension: £51,000-£92,000 upwards

Wales' separate planning rules

Since the Planning (Wales) Act 2015, Wales has administered planning under its own legislation, distinct from England - specific permitted development size and height limits differ, so always confirm with Cardiff Council rather than assuming an England-focused guide applies.

Pontcanna and Llandaff need extra care

Pontcanna's conservation area and the streets around Llandaff Cathedral typically require extensions to respect existing rooflines and materials more closely than the standard Victorian terraces of Roath, Cathays or Grangetown, which can push costs toward the top of the range regardless of the extension's actual size.

What pushes costs up further

As in any Victorian terraced city, access on Cardiff's narrower streets remains a recurring cost driver - skip and scaffold permits are often needed where a street has no realistic space for either.