Single storey rear extension at a semi-detached house in a conservation area
Proposed: 5 m deep · 5 m high · 4 m eaves · 15 m² footprint.
of comparable applications near you were approved.
In shortYour design is too large to build without permission — but most comparable applications nearby were approved, and a few modest reductions would remove the need to apply altogether. This report explains why, and walks through both routes.
What’s specific about your property
Here’s what shapes this report: the Upper Street (North) Conservation Area, and your design goes beyond 3 of the limits it tightens. Everything else about your site is clear — the detail’s below.
7 constraint layers were checked against national and local datasets for your address. 6 came back clear — your property is not listed, not in a flood zone, not in the green belt, not in an AONB, free of Article 4 directions and free of tree preservation orders.
The one that matters is the conservation area. Your property sits within the Upper Street (North) Conservation Area, designated for its special architectural and historic character. This doesn’t prevent you building — but it tightens the permitted development limits that apply to your house, restricts how much the council will tolerate in terms of design and materials, and means your application will be assessed by a conservation officer as well as a standard planning case officer.
The conservation area is the single most important fact in this report. Every section that follows is shaped by it — the rules that apply to you, the risks you face, and what a successful application will need to look like.
How the law applies to your project
Permitted development rights are a legal shortcut — a set of rules that, if your project meets all of them, mean you can build without a planning application. We’ve tested your project against each one. The failures here are what require you to apply for permission.
We checked 12 rules from the Town and Country Planning Order 2015 (GPDO 2015, Schedule 2, Part 1, Class A) — the legislation that governs rear extensions on semi-detached houses. 3 failed, 1 triggered a warning, and 8 passed.
What the refused 5% can tell you
An overall approval rate of 95% is genuinely encouraging — but it’s an average, and averages hide things. The applications that get refused tell you exactly what Islington won’t accept, and some of those reasons apply directly to your project.
We analysed 24 refused decision notices for rear extensions in Islington over the last 3 years. The picture that emerges is consistent: refusals cluster around a handful of specific issues. 3 of them are directly relevant to what you’ve proposed.
264 decisions reviewed
4 points lower — this gap matters
The conservation area figure of 91% is the one that applies to you. That 4-point gap reflects the extra scrutiny conservation area applications attract. It’s still a strong majority — but it means roughly 1 in 11 applications in your situation are refused, rather than 1 in 20.
3 of the 5 most common refusal reasons apply to your project. That’s not a reason to give up — it’s a reason to take design seriously, and to use pre-application advice before committing to a full application.
What you can do from here
A planning permission requirement isn’t a dead end — it’s a fork in the road. You have three credible routes forward, and the right one depends on how much the extra size matters to you and how much time and cost you’re prepared to take on.
Whatever route you choose, the next section gives you a clear picture of what it will actually cost and how long it will realistically take — including the parts most people underestimate.
What you’re committing to financially and in time
Most people focus on the build cost and underestimate everything around it. Here’s the full picture — construction, professional fees, and a realistic timeline from today to breaking ground.
That figure covers structure, roof, and basic finishes. On top of it, budget separately for professional fees — the planning application fee (£548), an architect for drawings and Design & Access Statement (£2,000 – £5,000), and a structural engineer for foundation calculations and wall openings (£500 – £1,500). If your extension adjoins a neighbour’s wall, a party wall surveyor will also be required.
On timing, the planning determination period alone is 8 weeks. But the realistic total from deciding to proceed today to breaking ground is closer to five or six months, once you factor in finding an architect, producing drawings, submitting the application, and procuring a builder. Plan for this — don’t expect to be on site in six weeks.
These numbers assume you go the formal application route. If you redesign to permitted development size (see Section 4), you can cut the timeline roughly in half — no planning process, just building regulations approval.
What your neighbours have actually built
Approval rates are useful, but real decisions from real properties near yours are more informative. These are the same planning officers, the same local policies, and comparable properties — this is what they actually approve.
We identified 5 rear extension applications near your postcode , all 5 of which were granted — so rear extensions do get approved locally. But each was judged on its own merits, and yours still needs planning permission, so treat this as encouraging context rather than a guarantee.
The approvals near you show the council does grant rear extensions here — encouraging context, though yours still needs permission and will be judged on its own merits. The next section turns everything we’ve covered into a sequenced plan.
Your next steps, two ways
Both routes from Section 4, now as a step-by-step — with the time and cost of each.
You now have everything you need to move forward with confidence. If you want a report personalised to your actual address — with your real constraints, your council’s real decisions, and your specific project dimensions — it’s below.
What’s working for and against you
Your approval probability isn’t a single number pulled from thin air. It’s built from specific factors about your property, your project, and your local area — and each one pushes the odds up or down.
The factors are evenly balanced. A well-designed application with pre-application advice should tip the balance in your favour.
Maximum permitted development dimensions
These are the exact limits that apply to your property under GPDO Class A. Stay within every one and you don’t need planning permission.
Total ground coverage (all extensions + outbuildings) must not exceed 50% of the curtilage area.
These limits are personalised to your property type and conservation area status. Any dimension shown in amber has been reduced from the standard limit because of a constraint on your site.
Every project type assessed for your property
Your rear extension is one of many things you could build. Here’s every common project type, assessed against your specific property and constraints — so you can see what’s permitted, what’s blocked, and what needs a full application.
Permitted without an applicationYou have 8 project types available under permitted development. If your first choice needs planning permission, one of these alternatives might achieve what you want without the application process.
Professional services you’ll need
Different projects need different specialists. Here’s who you need, why, and what they typically cost — based on your specific project type and property constraints.
- Design sympathetic to the conservation area character
- Materials to match existing streetscape
- Planning application drawings and Design & Access Statement
- Building Regulations drawings
Fee ranges are indicative for London. Always get quotes from multiple professionals. Your architect or builder can often recommend other specialists.
Getting the right professionals involved early — especially before you commit to a design — is the single most effective way to avoid delays, cost overruns, and refusals.
Applying to Islington
Every council operates differently. Here are the specific fees, timelines, and links for making an application to Islington Council.
Islington has extensive Article 4 directions covering many conservation areas, which remove some permitted development rights. Pre-application advice is recommended for properties in conservation areas.
These links take you directly to Islington’s planning services. If you’re going the formal application route, pre-application advice is always the recommended first step.
This was a sample. Yours is about your home.
A full report personalised to your exact address — your council’s real decisions, your real constraints, your specific dimensions, cost estimate and tailored action plan.
Get my report — £9 →- Approval rates from your council’s own planning records — not national averages
- All 7 constraint layers checked against your exact postcode
- Full rules analysis for your project type and property
- Refusal reasons and design tips drawn from real decision notices
- Nearby precedents — what similar properties near you were approved to build
- Cost estimate based on your actual footprint
- Step-by-step action plan with professional fee guidance