Single Storey Extension in Chorley: Costs, Planning and Build

What a single storey extension typically costs in Chorley

For a straightforward rear or side extension in the Chorley area, most homeowners should budget somewhere between £2,000 and £2,800 per square metre for the shell and basic finish, and £3,000 or more per square metre once you add a fitted kitchen, underfloor heating, bifold doors and a higher spec of finish. A typical 4m by 5m rear extension therefore lands in the region of £45,000 to £65,000 all in, with plenty of room either side of that depending on choices.

The figures that catch people out are rarely the bricks and roof. Drainage diversions, moving a gas meter, a steel beam to open up the existing back wall, and upgrading an old consumer unit are all common on Chorley's older terraced and semi-detached stock. Ask any quote to show these as separate line items so you can see what is included and what is a provisional sum.

• Groundworks and foundations: usually 10 to 15 percent of the total, more if the ground is poor or drains need moving
• Structural steel and opening up: £1,500 to £4,000 depending on span and whether an engineer's design is needed
• Roof: a warm flat roof with a single ply or GRP finish is generally cheaper than a pitched tiled roof, but a pitched roof suits many Chorley homes better
• Glazing: bifolds and large sliders are often the single biggest line after the shell
• Professional fees: architect or plan drawer, structural engineer and building control, typically £2,000 to £5,000 combined

Planning permission and permitted development in Chorley

Many single storey extensions can be built under permitted development, which means no full planning application. For a detached house the rear extension can project up to 4 metres from the original rear wall, and 3 metres for a semi or terrace, with a maximum height of 4 metres and eaves no higher than 3 metres if within 2 metres of a boundary. The larger home extension scheme allows up to 8 metres and 6 metres respectively, but you must notify Chorley Council first through the prior approval process and neighbours are consulted.

Permitted development does not apply everywhere. Homes in conservation areas such as parts of Chorley town centre, Withnell and Wheelton, listed buildings, and properties where rights were removed on newer estates will need a full application. Corner plots and anything extending towards a road are also usually caught. A Lawful Development Certificate from the council costs a modest fee and is worth having even if you are confident, because it proves the extension was lawful when you come to sell.

Building regulations, drainage and the party wall side

Whatever the planning position, every extension needs building regulations approval. You can use Chorley Council's building control team or an approved inspector. They will check foundations, damp proofing, insulation, structural openings, fire safety and drainage. Expect inspections at excavation, foundation, damp proof course, drains and completion stages. Do not let anyone backfill a foundation trench before it has been looked at.

If you share a wall or are digging within 3 metres of a neighbour's foundations, the Party Wall Act applies. Serving notice is straightforward and most neighbours consent, but if they dissent you will need a surveyor, which adds a few weeks and typically £700 to £1,500 per side. Sort this before the start date is agreed, not the week the digger arrives. Also check for public sewers under the garden, which are common on older Chorley streets, as United Utilities may require a build over agreement.

How long the build takes and what to expect on site

A single storey extension of 20 to 30 square metres usually takes 8 to 12 weeks on site from first dig to handover, with the kitchen fit and decoration sometimes running a fortnight beyond that. Weather matters in Lancashire, so a winter start can stretch the groundworks phase. The order runs roughly as groundworks and drains, then brick and block to wall plate, roof on, windows and doors, then the internal trades of electrics, plumbing, plastering and second fix.

The knock through into the existing house is usually left until the new shell is watertight, so you keep a usable kitchen for most of the job. Agree in advance where skips and materials will sit, whether the crew of trades can use a toilet, and how power and water will be accessed. A written programme with stage payments tied to milestones protects both sides and makes it obvious if the job is slipping.

• Weeks 1 to 2: strip out, excavate, foundations, drainage, oversite
• Weeks 3 to 5: walls to wall plate, steel installed, roof structure
• Weeks 6 to 7: roof covering, windows and doors, watertight
• Weeks 8 to 10: first fix electrics and plumbing, insulation, plasterboard and plaster
• Weeks 10 to 12: second fix, flooring, kitchen or bathroom, decoration and sign off