Rule of thumb, extension prices can start from £1,100 per square meter (plus VAT) and rise well over 2600 per square meter (plus VAT) depending on factors such as quality of the house extension (basic, good, excellent) and complexity of construction, specification, features, shape, size, number of storeys, drainage, layout, site (trees, soil type, access, slope), location etc. For example a narrow and small extension will be more expensive than a square and big extension. The same extension in London will cost more than somewhere else. Kitchen cabinets, sanitary, appliances will add to price as they will vary depending on quality and your taste.
You may also need to consider if you can live in the house during the construction and if not, how this would increase the cost.
The following costs can be added additionally to a house extension costs:
Drawings and structural calculations for planning and building regulations (start from £800)
Party wall agreement (around £1000 if it is agreed surveyor)
Any internal alterations, rewiring, asbestos removal, new boiler system, decorations etc
Example 1: A single storey house extension or kitchen extension cost: 18 square meter (6m*3m) Single storey rear extension fully integrated with main house to provide open-plan living space, with bi-fold doors, roof lantern, and flat roof: Around £27000 plus VAT (20%), plus kitchen cabinets and sanitary. The house extension work can take around 2 months depending on site and weather situations.
Example 2: A double storey house extension cost: A double storey extension per square meter will be cheaper than a single storey extension as roofing and foundation cost can be similar. (Scaffolding will need to be added) 36 sqm (6m*3m) double storey rear extension: Around £50000 plus VAT (20%), plus kitchen cabinets and sanitary. The house extension work can take around 3 months depending on site and weather situations.
These are for only guidance. Remember, it's important to get multiple quotes for house extensions!
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