Not always. Most single-storey rear extensions fall within permitted development (PD) rights, meaning no formal planning application is required. Detached houses can typically extend up to 4 metres beyond the original rear wall; semi-detached and terraced houses up to 3 metres. However, if your property is in a conservation area, is a listed building, or your council has issued an Article 4 Direction removing PD rights, you will need full planning permission regardless of size. We strongly recommend checking your planning position before committing to any design work — a short conversation with a planning consultant can save months of delay.
A standard householder planning application takes 8 weeks (56 days) for your local planning authority to determine. However, complex applications, those in conservation areas, or those requiring revisions can take longer. Some councils in the region are currently exceeding the 8-week target during busy periods. If you use pre-application advice before submitting — which we strongly recommend — factor in an additional 6–12 weeks before your formal submission. Total realistic timeline from appointing a designer to receiving planning approval: typically 4–6 months. The earlier you start, the less pressure you feel.
Permitted development (PD) rights are a set of national rules that allow homeowners to carry out certain building works without applying for planning permission. For extensions, the key limits are: single-storey rear extension up to 4m (detached) or 3m (semi/terrace); side extensions up to half the width of the original house (single storey only); and no extension covering more than 50% of the total curtilage. PD rights may be restricted or removed if your home is in a conservation area, National Park, or AONB, or if the council has issued an Article 4 Direction. The safest way to confirm is to consult with a planning professional or submit a Pre-Application Enquiry to your local council.
Yes, in most cases. Conservation areas in Hampshire and Surrey significantly restrict permitted development rights. Side extensions and cladding changes are not permitted under PD in conservation areas. Rear extensions that would normally be PD may require prior approval or full planning permission. Materials must respect and complement the character of surrounding buildings — contemporary designs are not automatically refused, but must be carefully justified. Hampshire and Surrey have a high concentration of conservation areas, including Winchester city centre, Farnham, Godalming, and hundreds of village conservation areas. Always check your conservation area status before starting any design work.
A Lawful Development Certificate (LDC) is a formal document from your local council confirming that your building work was lawful under permitted development rights. It costs approximately £103 and can be applied for before or after the works are completed. While not legally required, we strongly recommend applying for one even when your project clearly falls within PD rights. When you sell your home, solicitors will ask whether any extensions were authorised. An LDC provides definitive, legally binding proof — which a verbal council confirmation does not. It is a small cost that prevents significant problems later.
Not necessarily — but you do need professional design drawings for almost any extension project. An architectural designer or planning and design consultancy can produce everything needed for planning applications and building regulations. For straightforward permitted development extensions, a good designer will suffice. For larger or more complex projects — conservation areas, listed buildings, or tricky planning constraints — a more experienced consultancy adds significant value. At Fortis, we work alongside Planning By Design, a multi-award-winning planning and design consultancy, who handle the full design and planning process for our clients across Hampshire and Surrey.
Always appoint your designer before your builder. This is one of the most important sequencing decisions in any project. Without drawings, a builder can only give you a ballpark estimate — which is largely meaningless for budgeting. With full planning and building regulations drawings, you can get three detailed, comparable quotes and make an informed decision. Appointing a builder before designs are finalised can also create conflicts of interest, as the builder may influence design decisions to suit their workflow rather than your brief. The correct sequence is: brief and budget → architect/designer → planning → building regulations → appoint builder → start on site.
For a straightforward extension within permitted development rights, the pre-build process typically takes 3–5 months: initial design (4–6 weeks), building regulations drawings and structural calculations (4–6 weeks), and building regulations approval (4–8 weeks). For projects requiring full planning permission, add 8–12 weeks for the planning process plus 6–8 weeks if you use pre-application advice. For conservation area projects or those requiring revisions, allow 6–10 months from appointing a designer to being ready to start on site. Our consistent advice: start the pre-build process earlier than you think you need to. Underestimating this timeline is the most common cause of project delays.
Yes, if your extension involves removing or altering a load-bearing wall, creating a new structural opening (such as for bifold doors or a wide span), adding a steel frame, or any work that affects the structural integrity of your existing building. The structural engineer produces calculations specifying the size and support requirements for any steelwork — which are required by building control before those elements can be inspected. For a standard extension, structural engineering fees are typically £500–£1,500. Never skip this stage or try to cut costs here — incorrect structural specifications are a safety risk and will prevent building regulations sign-off.
The Party Wall Act 1996 applies when your proposed building works are near, on, or below a party wall (a shared wall between two properties), a boundary wall, or within 3–6 metres of a neighbour's foundations. If the Act applies, you must serve a formal Party Wall Notice on all affected neighbours at least 2 months before work begins. If a neighbour consents, work can proceed normally. If they dissent or don't respond within 14 days, a Party Wall Award must be agreed through appointed surveyors. This typically takes 6–8 weeks and costs £800–£2,000 in surveyor fees. Build it into your timeline from day one.
Pre-build consultancy covers several distinct stages. Architectural design for a typical extension: £1,500–£4,000. Planning application fee (England): £206. Structural engineering calculations: £500–£1,500. Building regulations application: £500–£1,000. Lawful Development Certificate (if applicable): £103. Party wall surveyor fees (if applicable): £800–£2,000. Pre-application planning advice (if used): £75–£200. In total, budget approximately £3,000–£9,000 for the full pre-build process on a standard single-storey extension. This investment — typically just 5–10% of the total project cost — almost always saves significantly more than it costs by eliminating delays, redesigns, and unexpected build surprises.
Architectural design fees for domestic projects in Hampshire and Surrey vary by project complexity. Single-storey extension (planning + building regulations drawings): £1,500–£4,000. Loft conversion: £1,500–£3,500. Double-storey extension: £2,500–£5,000. New build residential: £5,000–£20,000+. Some designers charge a percentage of the build cost (typically 5–10%), others charge a fixed fee. Most consultancies offer a free initial consultation. Our pre-build partner Planning By Design provides no-obligation fee proposals for any residential project across Hampshire and Surrey.
Structural engineering fees for domestic extensions typically range from £500–£1,500 for a standard single-storey extension. For more complex projects — multi-storey extensions, underpinning, new structural frames, or large steel spans — fees can reach £2,000–£6,000. Structural engineers usually provide a fixed-fee quote based on a brief project description. Costs in Hampshire and Surrey are broadly in line with the national average, though project complexity has a far greater impact on cost than location. Always include structural engineering in your pre-build budget from day one — it is not optional if load-bearing work is involved.
For a typical single-storey extension in Hampshire or Surrey, total pre-build costs (everything before a builder starts on site) typically range from £3,500–£9,000. This covers: architectural design (£1,500–£4,000), structural engineering (£500–£1,500), building regulations application (£500–£1,000), planning application fee if required (£206), and a Lawful Development Certificate (£103). Add party wall surveyor fees (£800–£2,000) if building near a shared boundary. For projects requiring planning permission plus pre-application advice, total pre-build costs can reach £8,000–£12,000. On a £60,000–£150,000 build, this is a proportionately small and extremely worthwhile investment.
Yes. While Fortis Construction & Maintenance focuses on the build itself, we work closely with a trusted pre-build partner network — including Planning By Design, a multi-award-winning planning and design consultancy. When you come to us at the early ideas stage, we can refer you directly to the right pre-build support: architectural design, planning applications, permitted development assessments, structural engineering, and building regulations drawings. This means your designer and builder already have a working relationship before your project starts on site — which makes the whole process faster, smoother, and less stressful. Ask us about this at your initial consultation.
Planning By Design is a multi-award-winning planning and design consultancy operating across the UK and Ireland. They work with homeowners, developers, and commercial clients on the full spectrum of pre-build consultancy: architectural design, planning permission applications, permitted development assessments, Lawful Development Certificates, building regulations drawings, structural engineering calculations, and party wall matters. They are Fortis's preferred pre-build consultancy partner, and we refer clients to them regularly when professional planning and design input is needed. They have strong local knowledge of planning authorities across Hampshire, Surrey, and the wider South East.
A refusal is not the end of the road. You have several options: revise and resubmit addressing the stated reasons for refusal (free within 12 months of the original decision), appeal to the Planning Inspectorate (free to submit but can take 6–12 months), or seek pre-application advice to understand precisely what the council would accept before resubmitting. The decision notice will set out the exact reasons for refusal — read these carefully with your planning consultant. Working with an experienced planning consultant who knows your local authority's preferences dramatically reduces the risk of refusal in the first place. Our partner Planning By Design has a strong track record of successful applications across Hampshire and Surrey.
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