Free Extension Planning Guide - Winchester, Hampshire & Surrey

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Mistake 1: Assuming You Need Planning Permission When You Don't

Many homeowners pay for unnecessary planning applications because they don't understand Permitted Development Rights (PD). A large proportion of single-storey rear extensions in Hampshire can be built without any planning permission at all — up to 4 metres deep on a detached house, or 3 metres on a semi-detached or terraced property. Two-storey rear extensions up to 3 metres deep and 7 metres or more from the rear boundary may also qualify. Paying for an unnecessary planning application adds cost, delay and risk to your project. The first thing we do is establish your permitted development position before anything else.

Mistake 2: Assuming You Don't Need Planning Permission When You Do

The opposite problem — and more expensive. Building without planning permission when it was required means your extension is unlawful. You may have to demolish it, which can cost more than building it in the first place. PD rights are removed in conservation areas, on listed buildings, on some newer housing developments (where the developer included an Article 4 Direction), and in parts of the South Downs and New Forest National Parks. Winchester, Southampton and other Hampshire towns have extensive conservation areas. Always check before you build.

Mistake 3: Using Drawings That Aren't Sufficient for Building Regulations

Planning permission drawings and building regulations drawings are not the same. Planning drawings show the design intent — what the extension will look like. Building regulations drawings show the structural detail — how it will be built safely, meeting thermal performance, fire safety, structural adequacy and drainage requirements. Many homeowners receive planning approval with one set of drawings, then discover they need a completely different set before their contractor can start on site. Hampshire Build produces both as separate packages, and we're clear about what each includes.

Mistake 4: Not Checking Whether a Party Wall Agreement Is Required

If your extension is within 3 metres of a neighbouring property's foundations, or involves excavation within 6 metres of a neighbour's structure, the Party Wall etc. Act 1996 requires you to serve notice on your neighbour before starting work. Failure to serve notice can result in an injunction stopping your build, and the cost of resolving a party wall dispute far exceeds the relatively modest cost of managing it correctly from the start. Extensions to semi-detached or terraced Hampshire properties almost always require party wall notices. Loft conversions on shared roof spaces always do.

Mistake 5: Not Obtaining a Lawful Development Certificate for PD Work

Even when your extension doesn't need planning permission, it's wise to obtain a Lawful Development Certificate (LDC) from your local planning authority. An LDC is the council's formal confirmation that your extension is lawful under PD rights. Without one, you have no documented proof that the extension was lawful — which can create serious problems when you come to sell the property. Hampshire solicitors routinely ask for LDC evidence, and buyers' mortgage lenders often require it for extensions built in the last 10 years. We recommend LDC applications for all PD extensions.

Mistake 6: Choosing an Extension Designer Based on Price Alone

The cheapest set of drawings isn't the cheapest outcome. We regularly see applications submitted by others that are refused — sometimes for simple errors that could have been avoided with better preparation. A planning refusal delays your project by 3–6 months and adds the cost of a revised application or appeal. Our 98% planning approval rate across Hampshire is the result of careful pre-application research, quality drawings and an understanding of what local planning officers are looking for. A fixed-fee service from a specialist costs more than the cheapest draughtsman, but it costs far less than a refusal.

Mistake 7: Overlooking Ecological Survey Requirements

Hampshire has significant bat populations, and bats are a European Protected Species. If your project involves work to a roof (loft conversion, raising a roof, removing tiles), work to an outbuilding, or removal of trees or dense hedgerows, your planning authority may require a Preliminary Ecological Appraisal before determining your application. Winchester City Council, East Hampshire District Council and New Forest National Park Authority are all particularly thorough on this point. Discovering an ecological requirement after your planning application has been submitted can delay determination by 3–4 months while surveys are arranged. We identify ecological risk at feasibility stage.

Mistake 8: Starting Work Without a Proper Specification

A planning approval and a set of building regulations drawings are not the same as a construction specification. Without a proper specification, your contractor cannot price the job accurately, and you cannot compare quotes fairly. Variations and extras during construction are the single biggest source of budget overrun on Hampshire extension projects — and most of them stem from ambiguity in the original specification. Our Premium and Premium Plus packages include a full schedule of works to help Hampshire homeowners tender their project correctly and keep their build on budget.

Mistake 9: Not Budgeting for the Full Cost of Extension Design

The design and planning cost is only part of the total project cost — but it's the part that determines whether everything else goes smoothly. Underspending on design leads to poor drawings, planning refusals, building control queries, contractor disputes and cost overruns. Hampshire Build's fixed-fee model means you know exactly what you're paying for design services before you commit. Our Pre-Build Package starts at £1,950 + VAT, our Premium Package at £2,950 + VAT, and Premium Plus at £4,950 + VAT. There are no hidden charges, no hourly billing surprises, and no additional fees if planning takes longer than expected.