How much will my house extension cost?


Current at time of editing (03/2023).

Before extending your house one of the most important factors to review is the overall cost, not just the building cost.

Architect Fees

Fee proposals would either be a fixed fee, an hourly rate (including an estimate of hours) or a percentage fee of the construction cost (usually only for larger projects). Please contact us to discuss fees for your proposed project. We aim to provide fixed fees for our Work Stages 1 - 4A where possible.

Planning Fees
The Country Council reviews the planning application and requires a fee to be paid for this statutory service. A typical house extension planning fee is currently £206 (including VAT). We submit via the Planning Portal which also has a £64 admin fee charge.

Building Regulation Fees
The County Council both review the building regulation application and carry out inspections once the work has commenced. Two separate fees are payable to the Council for this service. This fee varies as it is usually assessed on the floor area of an extension or on the estimated overall construction cost. As an example, an extension with a floor area between 10-40 sq m is around £660 including VAT for the Council's Building Regulations fee (application review and inspections included).

Structural Engineer's Fees
For all size projects, it is likely that the involvement of a Structural Engineer will be required. Their involvement is crucial to providing an assessment of the structural implications of a design and submitting structural calculations that are required by Building Control for the Building Regulations application. Their fees can range from £500+VAT to £1500+VAT depending on the complexity of the structural design.

Construction Cost Estimate
We can provide a Priced Estimate Schedule, via an Estimating Company, at Building Regulations stage to give a detailed estimate of cost. This can be a useful tool to compare against builder's Quotes or be used to facilitate more accurate builders quotes.. This schedule can also be used to seek detailed comparisons from builders. This service is an optional extra and is typically around £400.

Building Cost
Building construction costs vary considerably, however, a ‘ball-park' guide of cost can be calculated on a cost per square metre basis. This can typically be between £2,500 and £3,500 per sq m exclusive of VAT. The variation of costs would depend on the complexity, quality, materials and builders overheads. These costs per square metre would equate to a general finished extension cost, exclusive of large fitted items such as kitchens and bathrooms. We would suggest assuming around £3,000 per sq m (plus VAT) when planning a typical extension. Do allow for the floor area of all floors (ground and first floor for example).

Builders may be able to provide an estimate based on the Planning drawings, however, they would typically only provide a firm quotation once the Building Regulation drawings are available.

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