Cost: house extension
Separate new construction, opening to the house, roof and facade junctions, services and making good. A square-metre price does not describe those interfaces. No universal premium over new build or area discount is established.
Editorial update on 19 September 2026
Compare identical plans
Define measured area, room purpose and finishes. Separate design, excavation, foundations, structure, envelope and equipment. Identify allowances and exclusions.
Price existing-house work too
Include opening and planned structural alteration, junctions, service relocation and affected finishes in existing rooms. Define soil and waste removal, garden protection, access and reinstatement.
Control alternatives
Compare masonry, timber or modules on equivalent scope and confirmed feasibility. Ask about cost, timing and maintenance effects. Set validity, taxes and variation approval. Do not deduct aid merely because new space is insulated.
The three budget levels
Where your money goes
- StudiesOn quotationPosition and investigations.
- New volumeOn quotationFoundations, structure and envelope.
- InterfacesOn quotationOpening, roof and services.
- DeliveryOn quotationDefined finishes and surroundings.
What makes the price vary
Use
Rooms and equipment.
Existing house
Structure and connections.
Plot
Ground, access and position.
Organisation
Occupancy and phases.
Indicative scenarios
Separate new space and any renovation of the existing building. Verify the scheme and eligible project scope before counting funding. An insulated extension alone does not establish Klimabonus entitlement.
Frequently asked questions
Must heating be enlarged?
Assess needs and the installation. No automatic replacement or supplement is assumed.
Must materials match?
The authorised project and technical details determine choices, not appearance alone.
Can I remain at home?
Confirm safe routes, separation and usable services at each stage.
Should the garden be included?
Separate reinstatement after work from new landscaping; explicitly include or exclude each.
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