Planning Permission vs Permitted Development: What You Can Build
Quick Answer: Most single-storey rear extensions under 4m (terraced) or 6m (detached/semi-detached), loft conversions adding up to 40-50m³, and porches under 3m² fall under permitted development rights and don’t need planning permission. However, you’ll always need Building Regulations approval for structural work. Extensions over these limits, side extensions, front extensions, or properties in conservation areas typically require full planning permission. Check with your local planning authority before starting any work. Understanding the Difference: Planning Permission vs Permitted Development When you’re planning a home extension, conversion, or major renovation, one of the first questions you’ll face is: “Do I need planning permission?” The answer isn’t always straightforward, and getting it wrong can be costly. In the UK, there are two main routes for building work: planning permission (a formal application to your local council) and permitted development rights (work you can do without applying). Both still require compliance with Building Regulations, which is a separate approval process entirely. As plasterers working across Kent since 2008, we’ve seen countless homeowners confused by this distinction. Some delay projects unnecessarily thinking they need permission when they don’t. Others crack on with work that clearly needs approval, only to face enforcement notices and costly remediation. What Are Permitted Development Rights? Permitted development rights are a national grant of planning permission that allows certain building work and changes to your property without needing to apply for planning permission. These rights are set out in the Town and Country Planning (General Permitted Development) (England) Order 2015, which has been amended several times since — most recently expanding rights for rear extensions and loft conversions. Think of permitted development as a set of rules that say “you can do X as long as you stay within Y limits.” Stay within those limits, and you’re free to proceed (after Building Regs approval). Go beyond them, and you’ll need to submit a planning application. Key Permitted Development Categories for Homeowners Class A: Extensions and alterations to houses Class B: Additions to the roof of houses (dormers, skylights) Class C: Other alterations to the roof (roof height increases) Class D: Porches Class E: Outbuildings (sheds, garages, summer houses) Class F: Hard surfaces (driveways, patios) What Can You Build Under Permitted Development? Here’s where the rubber meets the road. The specific limits vary depending on your property type and location, but these are the general rules as of 2026: Single-Storey Rear Extensions Single-storey rear extensions are the most common project we see on sites, and the rules are relatively generous: Property Type Maximum Depth Maximum Height Detached house 8m from original rear wall 4m to eaves, not exceeding existing roof Semi-detached or terraced 6m from original rear wall 4m to eaves, not exceeding existing roof Important conditions: The extension cannot cover more than 50% of the land around the original house (excludes original footprint). The roof pitch must match the existing house if within 2m of the boundary. Side-facing windows above ground floor must be obscure-glazed. Pro Tip: If you’re building right up to a boundary, you may need to serve a Party Wall Notice even if your extension is permitted development. This is separate from planning and protects your neighbour’s rights. Larger Single-Storey Extensions (Prior Approval Route) Since 2013, you can build single-storey rear extensions beyond the standard limits under a “prior approval” process: Detached houses: Up to 8m depth (same as standard permitted development) Semi-detached and terraced: Up to 8m depth (2m more than standard) You must notify your local planning authority and adjoining neighbours. Your neighbours have 21 days to raise objections. The council then has 42 days to decide whether the impact on amenity (light, privacy) is acceptable. If approved or no response, you can proceed. This costs around £116 in 2026 compared to £462 for full planning permission. Two-Storey and Side Extensions Two-storey extensions have tighter restrictions and often need full planning permission: Maximum depth: 3m beyond the original rear wall Cannot extend beyond the side of the original house Maximum eaves and ridge height cannot exceed the original house No verandas, balconies, or raised platforms Materials must be similar in appearance to the existing house Most side extensions require full planning permission because permitted development rights are very limited for work that extends beyond the original side wall. After working on dozens of extension projects across Kent, we always advise clients to budget for planning permission when extending sideways. Loft Conversions and Roof Extensions Loft conversions are popular because they add valuable space without expanding the footprint. Under permitted development, you can add: Property Type Maximum Additional Volume Terraced house 40m³ Detached or semi-detached 50m³ Key restrictions for roof work: No extension beyond the plane of the existing roof slope on the principal elevation (street-facing) Materials must be similar in appearance to existing No verandas, balconies, or raised platforms Roof extensions must be set back at least 20cm from the eaves Side-facing windows must be obscure-glazed and non-opening unless 1.7m above floor level Roof lights (Velux windows) on the rear slope are usually fine under permitted development as long as they don’t project more than 150mm from the roof plane. Porches You can add a porch without planning permission if: Ground floor area doesn’t exceed 3m² No part is more than 3m above ground level No part is within 2m of a boundary with a highway Outbuildings (Sheds, Garages, Garden Rooms) Outbuildings are permitted development provided: They’re single-storey with maximum eaves height of 2.5m and overall height of 4m for a dual-pitched roof or 3m for any other roof If within 2m of a boundary, maximum height is 2.5m Buildings and ground area don’t cover more than 50% of land around the original house Not used as separate living accommodation What Always Needs Planning Permission? Regardless of size, certain types of work always require planning permission: Front extensions (beyond minor porches) Significant side extensions that extend beyond the original house width New separate dwellings (including converting a garage into a granny annexe) Changes of use
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