The UK planning system is one of the most complex in the world. Getting it wrong can result in enforcement action, demolition orders, or an inability to sell your property. Getting it right can add tens of thousands in value. Here is a practical guide to what requires permission and what does not.\n\nPermitted Development Rights — Certain types of work are automatically permitted without needing to apply for planning permission, provided you meet specific conditions. For houses (not flats or maisonettes), permitted development includes single-storey rear extensions up to 6 metres (semi-detached) or 8 metres (detached) under the larger home extension scheme (requires prior approval notification). Loft conversions adding up to 40 cubic metres (terraced and semi-detached) or 50 cubic metres (detached), provided the highest point does not exceed the existing roof height. Outbuildings (sheds, summerhouses, home offices) that are single storey, not forward of the principal elevation, and cover no more than 50% of the curtilage. Porches up to 3 square metres that are less than 3 metres high and more than 2 metres from a boundary with a highway. Internal alterations (removing non-load-bearing walls, converting rooms). Replacement windows (with caveats for conservation areas). Solar panels on roofs (not facing a highway in conservation areas).\n\nWhen You Need Full Planning Permission — Any work that exceeds permitted development limits requires a full planning application. This includes extensions larger than permitted development limits, new builds on garden land (often classed as backland development), change of use (converting a house to flats, or commercial to residential beyond permitted development classes), building higher than the existing property, any work in a conservation area that affects the external appearance (even relatively minor changes), any work on a listed building (which also requires separate listed building consent), any work in a National Park, AONB, or the Norfolk or Suffolk Broads where permitted development rights are restricted.\n\nThe Application Process — A full planning application to your local planning authority costs 578 for a householder application (as of 2025). It requires completed application forms, site location plan and block plan (to scale, usually 1:1250 and 1:500), floor plans and elevations of proposed works, a design and access statement (for some applications), and potentially additional reports (flood risk assessment, ecology survey, tree survey, heritage statement). The statutory determination period is 8 weeks for householder applications and 13 weeks for major applications. In practice, many councils take longer. You can appeal to the Planning Inspectorate if your application is refused or if the council fails to decide within the statutory period.\n\nPrior Approval — Some permitted development rights require prior approval from the council before work begins. This is a lighter-touch process than full planning — the council can only consider specific matters (usually transport, flooding, contamination, or external appearance) and must respond within 56 days. If they do not respond, approval is deemed granted. Prior approval is required for larger home extensions, office-to-residential conversions (Class MA), agricultural-to-residential conversions (Class Q), and certain changes of use.\n\nLawful Development Certificates — If you want formal confirmation that your proposed work falls within permitted development, apply for a Lawful Development Certificate (Proposed). This costs 289 and the council confirms in writing whether the work is lawful. This is invaluable when selling — buyers and their solicitors want certainty. If work has already been completed without permission and you believe it was permitted development, you can apply for a Lawful Development Certificate (Existing). If the work was carried out more than four years ago (10 years for change of use), it becomes immune from enforcement regardless of whether it was lawful.\n\nArticle 4 Directions — Local authorities can remove permitted development rights in specific areas using Article 4 directions. This is common in conservation areas and some HMO-heavy neighbourhoods. If Article 4 applies to your property, you need planning permission for work that would otherwise be permitted. Check your local authority's planning pages before assuming permitted development rights apply.\n\nBuilding Regulations — Planning permission and building regulations are separate systems. You can have planning permission but still need building regulations approval (and vice versa). Most structural work, electrical work, plumbing, and any work involving fire safety requires building regulations sign-off. A building regulations completion certificate is essential for selling — its absence is one of the most common issues raised during conveyancing. If previous work was done without building regulations approval, you may need to apply for retrospective approval or obtain indemnity insurance.\n\nPractical Advice for Developers — Pre-application advice from the planning department costs 100 to 600 depending on the council but can save thousands in wasted application fees and redesign costs. Engage a planning consultant for anything complex — their fee typically pays for itself through a higher chance of approval. Always check the local plan — the council's policies on density, character, parking, and green space strongly influence decisions. Neighbour objections matter but are not decisive — the planning officer makes the recommendation based on policy, and the committee (if it goes that far) decides.