House Extensions

What Does a House Extension Involve?

A house extension adds new living space to your existing property by building outward (rear or side), upward (double storey) or wrapping around the building. Most extension projects start with an initial site survey and design consultation, followed by architectural drawings, structural engineering calculations, and either a permitted development check or a full planning application. The build itself involves foundations, masonry or timber frame walls, a new roof structure, windows and doors, and full integration of electrics, plumbing and heating into the existing house. MTD Building Contractors manage the entire process — from the first sketch through to the final snag list and handover.

House Extension Costs

A single storey extension typically costs between £1,500 and £2,500 per square metre in Worcestershire and surrounding counties. A standard 4m × 5m rear extension (20 sqm) would therefore range from £30,000 to £50,000 depending on specification. Double storey extensions cost approximately 50–60% more than a single storey of the same footprint, making them significantly better value per square metre of usable space. Key cost factors include the size and complexity of the design, ground conditions (clay soils common across the region may require deeper foundations), structural steelwork for open-plan layouts (typically £2,000–£5,000), and the level of internal finish. Professional fees for architectural drawings, structural engineering and planning applications typically add 10–15% to the build cost.

Planning Permission and Building Regulations

Many single storey rear extensions fall under permitted development rights, meaning no formal planning application is needed — provided the extension meets specific size, height and boundary limits. However, properties in conservation areas, listed buildings, flats, and extensions that exceed permitted development limits will require full planning permission from the local authority. All extensions require building regulations approval regardless of whether planning permission is needed. This covers structural integrity, fire safety, thermal efficiency and drainage. MTD Building Contractors handle the full regulatory process, including liaising with building control inspectors during construction.

Materials and Specification

We build extensions using traditional masonry construction (blockwork inner leaf, cavity insulation, brick or render outer leaf) or timber frame where appropriate. Roof structures are typically constructed using engineered timber trusses or cut rafters, with options for flat roofs, pitched roofs or a combination. Common specification choices include aluminium bi-fold or sliding doors, roof lanterns and skylights, underfloor heating, engineered oak or porcelain tile flooring, and high-performance double or triple glazing. We work with clients to set a specification that balances budget with long-term quality and energy efficiency.

How Long Does a House Extension Take?

A single storey rear extension typically takes 10–14 weeks on site from breaking ground to completion. A double storey extension usually takes 14–20 weeks. Before construction begins, allow 6–12 weeks for the design, planning and building regulations process. The full project timeline from first enquiry to moving in is typically 6–9 months. MTD Building Contractors provide a detailed programme at the start of every project so you know exactly what to expect and when.