4m & 3m Limits: Permitted Development Heights for Extensions in England

A single-storey extension must not exceed 4 metres in height, and where any part sits within 2 metres of a boundary, the eaves cannot exceed 3 metres. No enlargement, whatever its size, can rise above the highest point of the existing roof. Larger single-storey rear extensions can reach 6 metres (terraced or semi-detached) or 8 metres (detached) via the prior-approval route, but the 4-metre height cap still applies. Previous extensions or high land coverage can knock you out of these limits entirely.

TL;DR:

• Extensions within 2 metres of a boundary must have eaves height limited to 3 metres to remain within permitted development rights.
• Any single-storey extension cannot exceed the highest point of the existing roof, regardless of its overall height, including larger rear extensions up to 8 metres.
• A prior-approval process is required for rear extensions exceeding 4 metres in depth (up to 6 or 8 metres), with a 21-day neighbour consultation period before starting construction.
• Accurate ground level and roof measurements are crucial, especially on sloping sites, to ensure compliance with height and eaves restrictions.
• Land coverage limits, including previous extensions and outbuildings, must stay within 50% of the curtilage area, or permitted development rights are lost.

Table of Contents

• What are the permitted development height limits for extensions?
• How do you measure extension height and eaves correctly?
• When does a larger rear extension need prior approval?
• What is the ‘original house’ rule and the 50% coverage limit?
• What edge cases and mistakes commonly void permitted development?
• A step-by-step checklist before you commission drawings
• How does an integrated design-and-build service reduce PD risk?
• What homeowners consistently get wrong about “permitted development”
• Get your rear extension designed, approved, and built with one team
• Key legislation and official guidance to check
• Sources
• FAQ

What are the permitted development height limits for extensions?

The rules sit inside Schedule 2, Part 1, Class A of the Town and Country Planning (General Permitted Development) (England) Order 2015, and they are more specific than most homeowners expect. Class A is not one blanket rule. It is a set of conditions, and every single one has to be met simultaneously for a project to count as permitted development.

The basic height restriction lives in paragraph A.1(f): a single-storey rear or side extension must not exceed 4 metres in height, full stop, wherever it sits on the plot. Paragraph A.1(f) also introduces a boundary-proximity rule that catches out more homeowners than any other single clause: if any part of the extension is within 2 metres of the boundary of the curtilage, the eaves height of that part must not exceed 3 metres. It doesn’t matter whether the extension itself is 4 metres or 3.2 metres tall overall. Go over on eaves height near a boundary, and permitted development stops applying.

Side extensions get their own clause, A.1(j), which requires that a side extension be single-storey and not exceed 4 metres in height, alongside width restrictions relative to the original house. Two-storey extensions and loft conversions fall under different provisions again (A.1(g) covers the larger single-storey rear route, while two-storey rear extensions are addressed separately and capped so the enlargement cannot exceed the height of the highest part of the existing roof).

Here is the condition that trips up more ambitious projects than any height figure: whatever you build, under Class A, the enlarged part must never exceed the height of the highest part of the existing roof. A bungalow with a low roofline cannot suddenly sprout a taller rear addition just because it fits under the 4-metre single-storey cap; the two rules apply together, and the stricter one wins.

The main thresholds, side by side:

• Single-storey rear/side extension: maximum 4 metres in height, anywhere on the plot.
• Within 2 metres of a boundary: eaves height capped at 3 metres for that part of the extension.
• Larger single-storey rear extension (paragraph A.1(g)): up to 6 metres (attached houses) or 8 metres (detached houses) in depth, via the neighbour consultation scheme, but height still capped at 4 metres.
• Any extension, of any size: cannot exceed the height of the highest part of the existing roof.
• Two-storey and loft-conversion work: governed by separate paragraphs with their own eaves-matching and roof-height rules, generally stricter than the single-storey provisions.

None of this replaces building regulations approval, which is a completely separate legal process. Permitted development tells you whether you need planning permission; building regulations tell you whether the structure is safe, insulated, and fire-compliant. You can have full permitted development rights and still need building control sign-off on foundations, drainage, and structural calculations before a single brick goes up.

How do you measure extension height and eaves correctly?

Height is measured from ground level immediately adjacent to the extension, not from an arbitrary datum point or the original house’s floor level. That distinction matters more than it sounds. On a sloping site, “ground level” for measurement purposes is the ground as it exists next to the wall in question, and the GOV.UK technical guidance is explicit that you cannot use imported or built-up ground to artificially reduce the measured height of a structure.

Eaves height is measured to the point where the external wall meets the roof slope, essentially the bottom edge of the roof, not the ridge and not an internal ceiling line. Where flat roofs are involved, the “eaves” reference point becomes the top of the wall, since there’s no slope to define it otherwise.

Pro Tip: On a sloping garden, get a proper measured survey rather than eyeballing levels from a tape measure and a spirit level. Planning officers see disputed ground-level assumptions regularly, and a documented survey in your submission removes that argument before it starts.

A few protrusions matter and a few don’t:

1. Parapets and raised roof edges on the new extension count towards its measured height. If you’re adding a parapet detail for a flat-roof look, that height goes into the calculation.
2. Chimneys, flues, and small roof features on the existing house are usually excluded when assessing the height of “the highest part of the existing roof” for comparison purposes, since Class A is concerned with the main roof form.
3. Solar panels and satellite dishes are typically ignored for these height calculations, as they fall under different permitted development provisions entirely.

Two worked examples make this concrete.

Flat-roof single-storey rear extension. Say your garden slopes gently away from the house, dropping 300mm over the depth of a proposed 4 metre by 6-metre extension. You measure height from the ground level at the base of the extension wall, not from the original patio slab three metres away. If the wall height plus roof buildup reaches 3.9 metres at the highest point, you’re inside the 4-metre cap. But if part of that extension sits 1.5 metres from the side boundary and you’ve specified a raised parapet edge that pushes the eaves line to 3.2 metres, you’ve breached the 3-metre eaves limit for boundary-proximity extensions even though the overall height is compliant.

Pitched-roof rear extension. Here the eaves height (where wall meets roof slope) is what gets checked against the 3-metre boundary rule, while the ridge height gets checked against the 4-metre overall cap and against the existing roof height. A pitched roof extension 5.5 metres from any boundary has more flexibility. It only needs to satisfy the 4-metre overall height limit and the “no taller than the existing roof” test, because the 2-metre boundary trigger for the stricter 3-metre eaves rule doesn’t apply.

When does a larger rear extension need prior approval?

Extensions that exceed the standard single-storey depth limits, but stay within 6 metres (semi-detached or terraced houses) or 8 metres (detached houses), fall under paragraph A.1(g) and require what’s called the neighbour consultation scheme, better known as prior approval. Height is still capped at 4 metres; this route only extends how far back you can build, not how high.

The process works differently from a standard planning application, and the timings matter because starting work at the wrong moment invalidates the whole thing. Once you submit a prior approval application, the local planning authority notifies adjoining neighbours and gives them 21 days to raise objections about the impact on their amenity, typically loss of light or an overbearing sense of enclosure. The council then has a statutory period within which to issue a decision on your application.

Here’s the part homeowners get wrong most often: you cannot start work until one of three things happens; the council confirms prior approval isn’t required, the council grants prior approval, or the 42-day period expires without a decision. Breaking ground early, even by a few days, can undo the prior-approval process entirely and expose the whole extension to enforcement action.

What actually improves your odds of a clean approval:

• Submit clear, scaled elevations showing the extension in context against neighbouring properties, not just the extension in isolation.
• Include a short written statement addressing likely amenity concerns directly, particularly daylight and overshadowing to habitable rooms next door.
• Show boundary distances and eaves heights explicitly on the drawings, since these are the two figures assessors check first.
• Keep a paper trail of any informal conversation with neighbours before submission; councils respond well to evidence that impact has been considered.

Local authorities aren’t grading your extension on taste. They’re checking a narrow, specific question: does this affect the amenity of adjoining occupiers? Drawings that answer that question directly, rather than simply looking professional, tend to sail through faster. The Planning Portal notes that this consultation is a genuine assessment, not a formality, and neighbours do use their 21-day window.

What is the ‘original house’ rule and the 50% coverage limit?

Permitted development allowances are calculated against the “original house,” which the technical guidance defines as the house as it existed on 1 July 1948, or as first built if constructed after that date. This single definition catches out an enormous number of homeowners buying period properties that have already been extended by a previous owner.

If a previous owner added a rear extension in 2004, and you want to add another one now, your available permitted development allowance is whatever remains after that earlier extension is counted against the total. You don’t get a fresh allowance just because you didn’t build the first extension yourself.

The second constraint that trips people up is the 50% curtilage coverage rule. Permitted development does not allow enlargement, improvement, or other buildings within the curtilage of the house to cover more than half of the total area of the curtilage, excluding the footprint of the original house itself. This calculation has to include:

• Any previous extensions, whenever they were built.
• Permanent outbuildings such as garages, garden rooms, or large sheds with a solid base.
• The new extension you’re now proposing.

A worked example shows how quickly this adds up. Take a house with a curtilage of 300 square metres. A previous owner added a 25 square metre rear extension and built a 15 square metre garden studio with power and a solid slab base. That’s 40 square metres already committed. If your new single-storey rear extension is planned at 35 square metres, your running total sits at 75 square metres, comfortably under the 150 square metre coverage limit (half of 300). But a similar house with a 120 square metre curtilage, the same 40 square metres of prior coverage, and a 35 square metre new extension is now at 75 square metres against a 60 square metre limit, over the cap before construction even starts. The extension itself might be entirely compliant on height and eaves, and it would still fail on land coverage alone.

Checking planning history through your local planning authority before commissioning drawings saves a lot of wasted design fees.

What edge cases and mistakes commonly void permitted development?

Certain land designations remove permitted development rights outright or restrict them further, and homeowners frequently don’t realise their property falls into one of these categories until an architect or planning officer flags it. Article 2(3) designated land, which includes conservation areas, National Parks, the Broads, and Areas of Outstanding Natural Beauty, imposes tighter restrictions on rear extensions and often removes permitted development rights for side extensions and cladding changes entirely. Sites of Special Scientific Interest carry their own additional constraints. If your property sits inside any of these designations, checking with the local planning authority before assuming permitted development applies isn’t optional, it’s the first step.

Beyond designated land, the mistakes that recur most often are procedural rather than technical:

• Mismeasuring eaves height by using the ridge line or an internal ceiling height instead of the actual wall-to-roof junction.
• Ignoring a previous extension’s contribution to the original-house allowance, assuming a “fresh start” that doesn’t exist in law.
• Starting construction before a prior approval decision or the 42-day expiry, which is one of the most common enforcement triggers on larger rear extensions.
• Building forward of the principal elevation, which permitted development does not allow regardless of height compliance elsewhere on the extension.

Pro Tip: If your property has already had a loft conversion, a previous side return, or an outbuilding added by a prior owner, treat the 50% coverage check and the original-house baseline as your first calculation, not your last. It’s the single most common reason a seemingly straightforward rear extension needs a full application.

The Planning Portal is direct about the practical consequence here: permitted development is entirely conditional, and breaching a single limit, height, coverage, boundary distance, or roof-forward positioning, takes the whole project outside permitted development and back into a householder planning application. There’s no partial credit. When any of these edge cases apply to your property, a full application, submitted with proper drawings from the outset, is usually faster and less risky than trying to force a project into permitted development that doesn’t quite fit.

A step-by-step checklist before you commission drawings

Getting the sequence right here saves money on redesign fees and prevents the awkward conversation with a planning officer three months into a project.

1. Measure and record your existing eaves height, ridge height, and boundary distances. Do this on-site with a tape measure and, ideally, a laser level, noting exactly where the ground level sits relative to each wall you’re extending from.
2. Check the planning history of the property through your local planning authority’s public register or the Planning Portal to establish the original-house baseline and identify any extensions or outbuildings added since 1948.
3. Calculate total enlargement and curtilage coverage, including every shed, garage, and outbuilding with a solid footprint, against the current total plot area.
4. Decide whether the larger single-storey route requires prior approval, and if so, prepare simple elevational drawings alongside a short neighbour-impact statement covering daylight and overshadowing.
5. Commission professional drawings, or get an integrated design-and-build quote, once you’re confident on the numbers but before you commit to a build date, since a surveyor or architect will catch measurement or coverage errors a homeowner’s tape measure might miss.

Steps one through three take an afternoon with a tape measure and a laptop. Step four is where most people either save weeks by confirming they don’t need prior approval, or discover early that they do and can plan around the 42-day window rather than being surprised by it mid-project.

How does an integrated design-and-build service reduce PD risk?

Most permitted development failures come down to one of two things: a measurement taken slightly wrong, or a planning history nobody checked properly before drawings were finalised. Both are avoidable, but only if the same team handles the survey, the design, and the planning check together, rather than passing information between three separate contractors who never speak to each other directly.

The Extension Works runs an instant online quote and live 3D modelling process specifically to close that gap. Because the design, planning assessment, and construction sit under one in-house team, boundary distances, eaves heights, and existing roof measurements get checked once, accurately, and carried straight through into the drawings used for any prior-approval submission. That matters most on the properties where permitted development gets complicated: irregular boundaries, a previous extension nobody has documents for, or a rear plot with a slope that makes ground-level assumptions genuinely ambiguous.

Homeowners in exactly those situations, a boundary within 2 metres on one side, an extension already added by a previous owner, or simple uncertainty about whether a project needs prior approval, tend to benefit most from a single accountable team rather than juggling a separate architect, planning consultant, and builder. A fixed VAT-inclusive price and a 12-month workmanship warranty also mean the compliance work isn’t a separate, unbudgeted line item discovered halfway through.

What homeowners consistently get wrong about “permitted development”

The biggest misconception isn’t about the numbers, it’s about what permitted development actually is. It’s not a category of extension that’s automatically approved. It’s a narrow set of conditions, and the moment one of them isn’t met, you’re not doing a “smaller” project that needs less paperwork, you’re doing an unauthorised development that needs a full planning application, retrospectively if necessary.

I’d argue the single most useful thing a homeowner can do before commissioning anything is treat the 4-metre height limit and the 50% coverage rule with equal seriousness. Most people obsess over the height figure because it’s the headline number, and then get caught out by land coverage because nobody totted up the shed, the old side return, and the new extension together. Enforcement notices rarely happen because someone deliberately built something enormous. They happen because a genuinely well-intentioned homeowner didn’t check what a previous owner had already used up.

Respect the prior-approval timings too. Starting early because you’re confident the council won’t object isn’t a shortcut, it’s a gamble that voids your permitted development rights if it goes wrong. For anything within 2 metres of a boundary, on a sloping site, or on a property with any prior extension history, get a professional measured survey before you finalise drawings. It costs far less than redesigning after a planning officer flags a height breach at submission stage.

— Esskay

Get your rear extension designed, approved, and built with one team

If everything above has told you anything, it’s that the risk in permitted development isn’t the headline height figure, it’s the measurement errors, planning history gaps, and process timing mistakes that sit underneath it. The Extension Works exists precisely to remove that risk from a single-storey rear extension: one in-house team handles the survey, the live 3D design, the planning and prior-approval checks, and the build itself, with a fixed VAT-inclusive price agreed upfront rather than discovered halfway through.

That matters most for the situations this article has covered in detail, a boundary within 2 metres, a previous extension you need factored into your original-house calculation, or genuine uncertainty about whether your project needs the neighbour consultation scheme. Rather than commissioning a survey from one firm, drawings from another, and a planning check from a third, you get one accountable team carrying the same measurements through every stage. Every project also comes with a 12-month workmanship warranty once building starts.

If you want a straight answer on where your extension sits against these limits, start with the instant online quote tool to see indicative scope and pricing, or look at how the single-storey rear extension service works from first sketch to sign-off.

Key legislation and official guidance to check

The rules in this article come directly from statute and government guidance, and it’s worth checking the primary sources yourself before finalising any design, since local circumstances can vary.

• The Town and Country Planning (General Permitted Development) (England) Order 2015, Schedule 2, Part 1, Class A, the statutory basis for all householder permitted development rights.
• Permitted development rights for householders: technical guidance, the official GOV.UK explanation of measurement, thresholds, and the prior-approval process.
• Planning Permission: Extensions, Planning Portal’s practical guidance on conditions and the neighbour consultation scheme.
• Building regulations approval, the separate approval process that applies regardless of your planning permission route.

Always confirm designation status and planning history with your local planning authority directly. Article 2(3) land and site-specific conditions can override the general rules described here.

Sources

• The Town and Country Planning (General Permitted Development) (England) Order 2015
• Planning Permission - Extensions (Planning Portal)
• Building regulations approval

FAQ

Can I extend 4 metres without planning permission?

Yes, in most cases. A single-storey rear extension up to 4 metres in height falls within permitted development, provided eaves stay under 3 metres where the extension is within 2 metres of a boundary, and the extension doesn’t push total land coverage over 50% of the curtilage.

Can I extend more than 6 metres?

Only via the larger single-storey rear extension route under paragraph A.1(g), which allows up to 6 metres for terraced and semi-detached houses, or 8 metres for detached houses. This route requires prior approval through the neighbour consultation scheme, and the overall height limit of 4 metres still applies regardless of depth.

What is the 2.5m height rule?

There’s no standalone boundary distance figure between 2 metres and 3 metres in the current permitted development legislation for extension height. The relevant boundary-related figure is the 3-metre eaves limit that applies within 2 metres of a boundary; some other figures sometimes appear in guidance relating to boundary walls, fences, or other structures rather than house extensions.

What are the height restrictions for permitted development in the UK?

For single-storey extensions in England, the core limits are a 4-metre maximum overall height, a 3-metre eaves limit within 2 metres of a boundary, and a rule that no enlargement can exceed the height of the existing roof. Two-storey and loft-conversion work is governed by separate, generally stricter clauses within the same Class A framework.

Does The Extension Works handle the prior approval process?

Yes, planning permission handling, including prior approval submissions for larger single-storey extensions, sits within The Extension Works’s in-house service alongside design and construction. Pricing for the full service, including a fixed VAT-inclusive quote, is available through the instant quote tool.

Recommended

• How big can a rear extension be under permitted development?
• Permitted Development & Extension Rules 2026 — How Big Can You Build?
• Get Completion Certificate: Building Regs for Extensions in England