🎥 Watch: House Extensions – 3 Quick and Easy Tips Before You Start Your Project
Prefer to watch instead of read?Here’s our quick 2-minute guide on House Extension rulesThinking about a house extension?
Send us a sketch and a few photos — we’ll tell you if it’s Permitted Development or needs full planning, and outline next steps.
At-a-glance: House extensions in the UK
House extensions can often be built under Permitted Development (PD), but design limits, boundaries, and local “quirks” decide what’s possible. This guide covers PD vs planning, costs, drawings, Building Control, timelines — and how councils interpret key rules like the 45-degree light test, overlooking/amenity, and materials to match. If you’re unsure, we can review your idea and map the safest approval route.
- Best first step: check if your idea is PD; if not, plan a smooth planning application.
- Key variables: height/width limits, proximity to boundaries, conservation/Article 4, parking & highway standards.
- Don’t forget: you still need Building Regulations approval even if the work is PD.
What counts as a “house extension”?
A house extension is a permanent enlargement of the original dwelling: rear or side additions, wrap-around extensions, two-storey rear wings, first-floor additions over existing structures, and infill links. Loft conversions are separate works (with their own PD rules), but can be combined with extensions in a single project if planned correctly.
Permitted Development vs full planning
Permitted Development (PD) lets you build certain extensions without a full planning application — if you meet specific limits on size, height, position, and design. If your proposal fails any PD rule, you’ll need Householder Planning Permission.
Typical PD parameters (England & Wales)
- Rear single-storey: maximum height often 4m; depth limited from the rear wall. The “larger home extension” prior approval route can allow deeper rear projections for many homes (subject to neighbour consultation).
- Side single-storey: generally no more than half the width of the original house; height typically up to 4m with limits near the boundary.
- Two-storey rear: usually restricted in depth and must meet separation distances; often requires full planning unless very tight criteria are met.
- Materials: “similar appearance” to the existing house is commonly expected under PD.
- Boundaries: being within 2m of a boundary can constrain height and eaves treatment.
- Designations: conservation areas, Article 4 Directions, and listed buildings can remove or restrict PD rights.
When PD isn’t possible or desirable (e.g., larger design ambitions, conservation constraints), a Householder Planning Application is the route. A well-argued design & access statement, daylight/sunlight checks, and context photos can make all the difference.
External references: Planning Portal | GOV.UK
Quick decision flow: which route fits?
- Sketch your idea (dimensions, storeys, roof type, doors/windows). Photograph the rear and side elevations.
- Check PD basics: past extensions, conservation/Article 4, proximity to boundaries, height/depth. If it passes → consider an LDC for proof.
- If it fails PD (or you prefer a bespoke design): plan a Householder Planning Application with drawings + statements.
- Either route: you’ll still need Building Regulations approval (Full Plans or Building Notice) before construction.
Typical timeline (survey → drawings → approval → build)
- Week 1–2: Measured survey + feasibility (PD check or planning route).
- Week 2–4: Concept drawings → client feedback → planning/PD-LDC set.
- Week 5–10: If planning: council validation and consultation ( ~8 weeks typical ). If PD-LDC: certificate determination (often similar timescale).
- Week 8–14: Building Regulations drawings, structural calcs, builder pricing.
- Start on site: appoint Building Control (Local Authority or Approved Inspector), book inspections, commence works.
Costs: drawings, approvals, build (£/m²)
| Item | Typical range (guide) | Notes |
|---|---|---|
| Measured survey + drawings (planning set) | £750–£2,000+ | Varies with complexity (single vs wrap-around/two-storey). |
| Lawful Development Certificate (LDC) fee | ~£100–£150 (householder) | Proves PD status before you build. |
| Householder planning application fee | ~£258 (England) + portal/LA charges | Council fees updated periodically; check your LA. |
| Building Regulations drawings pack | £900–£2,500+ | Includes details, specs, compliance notes. |
| Structural engineer calculations | £400–£1,500+ | Steel beams, padstones, foundations, etc. |
| Building Control (plan check + inspections) | £500–£1,200+ | Local Authority or Approved Inspector. |
| Build cost (single-storey) | ~£1,800–£2,800+ per m² | Spec, access, glazing, kitchens/MEP drive cost. |
| Build cost (two-storey) | ~£1,600–£2,600+ per m² | Economies of scale; fit-out choices matter. |
Related reads: Planning permission cost, Building Regulations, Building Control, Building Notice.
Documents & checklist
- Measured survey + drawings (existing & proposed plans/elevations/sections).
- Site plan, block plan, ownership certificate, community infrastructure screening (if requested).
- Design & Access Statement (planning) and/or Lawfulness statement (LDC).
- Daylight/sunlight or 45-degree assessment (if near windows of neighbours).
- Heritage statement (if conservation/listed or near listed buildings).
- Drainage and buildability notes; foundation approach near boundaries/trees.
- Structural calculations (steel beams, openings, foundations) for Building Control.
- Specifications: insulation, fire safety, ventilation, thermal bridging, glazing.
Council “quirks” to check early
Policies are national, but interpretation is local. Here are patterns we see across councils:
- 45-degree / 25-degree tests: Used to judge overshadowing and loss of light on neighbours’ main habitable windows. A slight set-in or lower eaves can resolve it.
- Overlooking & privacy: Side-facing clear-glazed windows near boundaries can trigger objections. Use high-level glazing, obscure glass, or angled windows.
- Materials to match: Many councils expect brick/roof tiles close to existing tones; mixed palettes usually need a stronger design rationale.
- Parking & highways: Some LAs require a minimum on-plot space after extensions. Losing a garage? Show where you still park.
- Corner plots & street scene: Side extensions visible from highways face stricter design control; step-backs and subordinate roofs help.
- Conservation / Article 4: PD rights may be curtailed; heritage statements and traditional detailing become key.
- Drainage near boundaries/trees: Build Over Agreements (public sewers) and root protection can change foundation design (e.g., piles, trenchfill).
Deep dives: Planning permission (pillar), Do I need planning permission?, Planning permission drawings.
Not sure if your idea fits Permitted Development?
We’ll check your project against PD rules and let you know if you need a full planning application.
Special cases — when to read a “Support Stone” next
- Kitchen extensions: drainage, extract, steel over long openings — see Do I need plans for my kitchen extension? and Kitchen extension planning permission.
- Garage conversions/links: parking standards, thermal upgrade, fire separation — Garage conversion guide and Do I need planning for a garage?
- Garden structures with connections: extensions vs outbuildings — compare Garden room rules and Shed planning.
- Regional nuances: examples at Buckinghamshire and Guildford.
Common pitfalls — and simple fixes
- Assuming PD without proof: Always verify. An LDC is cheap insurance.
- Ignoring neighbours early: Share sketches; minor tweaks can avoid formal objections.
- Over-glazing without performance: Meet Part L (thermal), Part O (overheating), and Part F (ventilation). Consider solar control glazing and shading.
- Flat roofs with poor upstands/falls: Specify warm roof build-ups and proper outlets; show details on drawings.
- Drain runs under new walls: Allow for lintels/protection or diversions — plan with your engineer.
- Light to existing rooms: Rooflights and internal windows can keep middle rooms bright after a wrap-around.
Conclusion
Whether you aim for a modest rear extension or a full wrap-around, success rests on three things: the right route (PD vs planning), clear drawings with evidence, and early attention to council quirks. We can confirm feasibility, produce compliant plans, and manage approvals so your build starts smoothly.
Interactive FAQs
Do I need planning permission or is my house extension Permitted Development?
Check depth/height, boundary distances, previous extensions, and whether you’re in a conservation area or under Article 4. If you pass PD thresholds, apply for a Lawful Development Certificate to lock certainty before you build.
Read next: Do I need planning permission?
What is the “larger home extension” prior approval route?
For many houses, deeper single-storey rear projections can be allowed via Neighbour Consultation/prior approval. The council notifies neighbours; if no valid objections or issues are resolved, approval is granted. It’s still technical — submit proper drawings and measurements.
How close can I build to the boundary?
Close-to-boundary designs are possible but affect height/eaves and guttering. Consider parapets, box gutters, or stepping away slightly. You may also need a Party Wall notice if you’re building near shared boundaries.
Will Building Regulations apply even if it’s PD?
Yes. You need Building Control approval and inspections covering structure, fire safety, insulation, ventilation, drainage, and electrics. Choose Full Plans for complex builds; Building Notice can suit simpler works.
Learn more: Building Regulations and Building Control.
How much does a house extension cost?
As a broad guide, single-storey shells can start around £1,800–£2,800+ per m², with two-storey from £1,600–£2,600+ per m², plus kitchen/bathroom fit-outs and finishes. Drawings, planning/PD-LDC, Building Control, and structural calcs are extra (see the table above).
Also see: Planning permission cost.
Do I need matching materials?
Under PD, “similar appearance” is typical. For planning, a good design rationale can justify contrasts (e.g., brick + zinc) — but sensitive areas favour matching or subordinate tones/details.
What about light/daylight to my neighbour?
Councils often apply the 45-degree/25-degree tests. Setting the extension back slightly, dropping eaves, or using a lean-to roof can resolve impacts while keeping usable space.
How long will approvals take?
Planning and PD-LDC decisions commonly take ~8 weeks from validation, but backlogs vary. We design for fewer clarifications and keep your build drawings moving in parallel.
Ready to move your project forward?
Plans Made Easy can prepare compliant plans, manage submissions, and guide you from idea to approval.
Next steps & useful guides
- Planning permission — Complete guide
- Do I need planning permission?
- Planning permission drawings
- Making plans
- Planning permission cost
- Do I need plans for my kitchen extension?
- Kitchen extension planning rules
- Planning permission for a garage
- Do I need planning for an extension?
- Planning permission — Buckinghamshire
- Garden room planning
- Planning permission — Guildford
- Garage conversion guide
- Building Regulations
- Shed planning rules
- What is Building Control?
- Building Notice route
External references for certainty: Planning Portal — National guidance, GOV.UK — Planning permission
