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Do I need planning permission for my home extension in Flintshire?

This is the first question almost every homeowner asks me — and the honest answer is: it depends. But in many cases, the answer is no. Let me explain.

What is Permitted Development?

Permitted Development rights allow homeowners to carry out certain types of building work without needing to apply for planning permission. The government grants these rights automatically — so as long as your project falls within the rules, you can go ahead without submitting anything to Flintshire County Council. This saves you the application fee, the wait, and the uncertainty.

What extensions qualify in Flintshire?

As a general guide, the following often qualify under Permitted Development:

• Single storey rear extensions up to 4 metres deep for detached houses, or 3 metres for semi-detached and terraced properties
• Extensions that don't exceed the height of the existing roof
• Side extensions up to half the width of the original house
• Loft conversions within permitted volume limits (typically 40-50 cubic metres)
• Garage conversions in most circumstances

When will I need planning permission?

Planning permission is likely to be required if your extension exceeds the Permitted Development limits above, if your property is in a conservation area or is a listed building, if previous extensions have already used your Permitted Development allowance, or if you live in a property where Permitted Development rights have been removed by a planning condition.

Mike's advice

Don't assume either way — let me check for you. At your site visit I'll assess your property, look at what you want to achieve, and tell you clearly whether planning permission is needed before a single penny is spent. In 25 years I've helped hundreds of homeowners across Flintshire avoid unnecessary planning costs by designing within Permitted Development limits wherever possible.

How much does a home extension cost in North Wales in 2025?

One of the most common frustrations homeowners tell me about is getting to the end of the design process and then getting a shock from the builder's quote. My job is to make sure that never happens to you. Here's a realistic breakdown of all the costs involved.

Build costs

In North Wales in 2025, typical build costs range from £1,500 to £2,500 per square metre depending on the finish, materials and complexity. A standard single storey rear extension of around 20 square metres might cost £30,000 to £50,000 to build. A double storey extension of 40 square metres could range from £70,000 to £120,000. These are guide figures — your builder will provide a fixed quote once the drawings are complete.

Architectural fees

Mike's fees cover the survey, existing and proposed drawings, planning application (if needed) and full building regulation drawings. A detailed written fee proposal is provided before any work begins so you know exactly what you're paying and what it covers.

Planning application fee

If planning permission is required, the fee for a householder application in Wales is £585 (from 1 December 2025) — Flintshire, Denbighshire and Wrexham all charge this national rate. In Cheshire West & Chester it is £548. Submitting via the Planning Portal adds a £91 service charge. These are paid directly to the council and portal — they are not part of Mike's fee. If your extension qualifies under Permitted Development, this cost is avoided entirely.

Building control fee

Building control fees vary depending on the size and type of work. For a typical single storey extension expect to pay in the region of £600 to £900 to either the local authority or a private building control inspector. Mike will obtain a quote for you once the design is finalised. This is paid directly by you and is not included in Mike's fee.

Other potential costs to be aware of

• Structural engineer — may be required depending on ground conditions, structural openings and roof design. Typically £500 to £1,500.
• Energy assessor — may be required for extensions with significant glazing. Mike will flag this early if it applies.
• Party wall agreement — if your extension is close to a neighbour's boundary a party wall surveyor may be needed.

Single storey vs double storey extension — which is right for you?

This is one of the most important decisions you'll make at the start of your project — and it's worth getting right. Here's my honest take after 25 years of designing both.

Single storey extensions

A single storey extension adds space at ground floor level — typically extending the kitchen, living area or dining room. It's the most popular choice for good reason.

• Lower build cost per square metre than a double storey
• Often qualifies under Permitted Development — no planning fee
• Less structural complexity — lower risk of additional costs
• Less disruptive to live in during the build
• Ideal for open plan kitchen-diner-living spaces

Double storey extensions

A double storey extension adds space on both ground and first floor — typically adding a bedroom, bathroom or home office above a kitchen or living extension.

• Much better value per square metre — you're doubling the footprint for a fraction of extra cost
• Adds significantly more value to your property
• Planning permission almost always required
• Greater structural complexity — foundations, steelwork, staircase
• Ideal if you need both living space and bedroom space

Mike's honest advice

If budget allows and you need more than one extra room, a double storey almost always represents better value in the long run. The cost difference between single and double is far less than most people expect — because the foundations, roof and walls are already being built regardless. But if your primary goal is a better kitchen or open plan living space and budget is a consideration, a well-designed single storey extension can be transformational. At your site visit we'll talk through your options honestly and help you decide what's right for your home, your family and your budget.