Estiquote

Local costs · Wales · September 2026

How much does an extension cost in Gwynedd?

A mid-range 25 m² single-storey extension in Gwynedd costs about £56,500 to £70,000 including VAT, or £2,300 to £2,800 per m² at Welsh prices. Gwynedd charges £684 for building control on a 10 to 40 m² extension (full plans, including VAT): the 13th cheapest of the 91 councils we checked, 19% below the typical council (£840). With design, a structural engineer, building control and a 15% contingency, budget £71,000 to £92,000.

By Estiquote · Prices reviewed · Council fees from Gwynedd's published schedule · How we calculate

Work out your project in Gwynedd

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Typical prices in Gwynedd

Mid-range finish, Wales prices, including VAT. The budget adds design and engineering fees, Gwynedd's building control charge and a 15% contingency.
ProjectBuilding workBudget to plan for
Single-storey extension, 25 m²£56,500 to £70,000£71,000 to £92,000
Double-storey extension, 40 m²£82,000 to £104,000£102,000 to £133,000
Dormer loft conversion, 30 m²£51,000 to £62,500£63,500 to £81,500
Kitchen, medium£8,600 to £15,200£9,800 to £17,500
Bathroom refit£5,600 to £8,500£6,500 to £9,700

Building prices in Wales run about 10% below the UK average outside London. Kitchens and bathrooms vary less from place to place than extensions and lofts.

Building control fees in Gwynedd

Gwynedd council charges including VAT (plan and inspection combined)
WorkCharge
Extension up to 10 m² (full plans)£456
Extension 10 to 40 m² (full plans)£684
Larger extension, 40-60 m² (full plans)£821
Extension 10 to 40 m² (building notice)£787
Loft conversion up to 40 m²£684
Garage conversion£456

Gwynedd charges £684 for building control on a 10 to 40 m² extension (full plans, including VAT): the 13th cheapest of the 91 councils we checked, 19% below the typical council (£840). Source: Gwynedd's building control charges, Version A19 dated 4 March 2026. Gross (inc VAT) columns.

Private approved inspectors set their own prices and are often competitive, so it is worth asking one or two for a quote as well. See how Gwynedd compares with every council we checked.

Notes on Gwynedd's schedule

Own schedule. Loft up to 50 m2.

Planning

In Wales, householder planning fees are set by the Welsh Government. Check the current fee on Planning Portal before you apply.

Other councils in Wales

Building control for a 10 to 40 m² extension:

Questions people ask

How much does an extension cost in Gwynedd?

A mid-range 25 m² single-storey extension in Gwynedd costs about £56,500 to £70,000 including VAT for the building work, or £2,300 to £2,800 per m², based on Wales prices reviewed in September 2026. With fees and a 15% contingency, budget £71,000 to £92,000.

How much is building control in Gwynedd?

Gwynedd charges £684 (including VAT) for a 10 to 40 m² extension (full plans), according to its published schedule (Version A19 dated 4 March 2026).

How much does a loft conversion cost in Gwynedd?

A mid-range 30 m² dormer loft conversion in Gwynedd costs about £51,000 to £62,500 including VAT for the building work, and about £63,500 to £81,500 with fees and a 15% contingency.

Before you get quotes