The eaves height rule within two metres of a boundary
Three metres of eaves height is tight once you allow for a floor build-up and a pitched roof. Here is where the two metres is measured from, how sloping ground is treated, and how to design with a margin.
The eaves height two metre boundary rule sits in Class A of Part 1 of Schedule 2 to the General Permitted Development Order 2015. Where any part of an extension comes within two metres of the boundary of the curtilage of the dwellinghouse, the eaves height of that part must not exceed three metres. Break it and the whole extension stops being permitted development, whatever else it complies with.
Three metres sounds generous until you build up from a finished floor. Once you allow for a slab, insulation, screed and a habitable ceiling height, the wall plate lands very close to the limit, and any pitched roof sits on top of it.
This is general guidance, not legal advice; check the position with your local planning authority or a qualified professional before relying on it. A Lawful Development Certificate is the only formal way to confirm that works are lawful.
Where the two metre measurement is taken from
The measurement runs from the boundary of the curtilage of the dwellinghouse to the nearest part of the enlarged part of the house. Two points in that wording catch people.
The first is curtilage rather than title. The relevant line is the boundary of the residential curtilage, which for most houses follows the garden boundary, but on a plot where part of the land is not within the residential curtilage, the line may sit inside the title boundary. If the plot includes a paddock or a strip that has never been used as garden, get the curtilage established before measuring.
The second is that every boundary counts. Side boundaries with neighbours, the rear boundary, and the boundary with a road or footpath all engage the rule. An extension across the back of a house with a narrow rear garden can be within two metres of the rear boundary without anyone noticing, and the eaves limit then applies even though no neighbour is affected.
Measure to the nearest part of the built form, including any part of the structure rather than only the wall face. And measure on the ground, not from a title plan, because title plans are not survey drawings.
The three metre eaves limit
The eaves height is the height at which the external wall meets the roof. For a pitched roof, that is the point where the plane of the wall, projected upwards, meets the upper surface of the roof slope. It is not the ridge and it is not the top of the fascia.
Only the part within two metres of the boundary has to comply. An extension that steps in, so that the section near the boundary has lower eaves and the section further away is taller, is a legitimate design response, and it is one of the few ways to get a full ceiling height under a pitched roof on a tight plot.
The limit sits alongside the other height controls in Class A rather than replacing them. A single-storey rear extension still cannot exceed four metres in overall height, and no part of the enlargement may exceed the height of the highest part of the existing roof, or have eaves higher than the existing eaves. All of them apply at once, and the most restrictive one governs.
Sloping ground and how height is measured
Height under the Order is measured from ground level, and where the ground is not uniform, the Order and the government's technical guidance for householders direct the measurement to be taken from a defined point rather than from wherever suits.
This matters on any sloping plot, because a wall that is 2.9 metres to the eaves at the top of a slope may be 3.4 metres at the bottom. The safest approach is to take levels along the whole length of the wall within two metres of the boundary, plot the eaves line against them, and check the worst case rather than an average. Then read the current technical guidance on which ground level applies, because it is the single point most often argued about, and get the authority's view in writing if the margin is small.
Where the ground falls away, three responses work. Step the eaves down with the ground. Lower the internal floor level so the wall plate follows. Or set the extension more than two metres from the boundary at the low end.
Excavating to reduce the measured height is not a reliable solution, because the ground level used is generally the level before the works rather than the level you create.
Flat roofs, parapets and upstands
Flat roofs are the usual way to keep within three metres, and they carry their own traps.
For a flat roof the eaves height is effectively the height of the external wall where the roof meets it. A parapet, an upstand, a roof light kerb or a plant screen above that line adds to the overall height of the extension, and the overall height limits still apply. So a flat roof at 2.9 metres with a 400 millimetre parapet is a structure 3.3 metres tall, which is fine against the four metre single-storey limit but is a different question against the eaves limit depending on how the authority reads the detail.
This is one of the points where practice varies between councils, so on a scheme designed to the limit it is worth a written query rather than an assumption. The consequence of being wrong is not a refusal. It is unauthorised development and an enforcement risk that surfaces at sale.
Also watch the roof build-up. A warm roof with a firring and a membrane can add more than expected between the design drawing and the finished job, and a 2.95 metre design becomes a 3.02 metre build.
Boundaries that are not straight
Suburban boundaries are rarely parallel to the house, and the rule applies at every point along the wall.
Where a boundary converges, part of the extension is within two metres and part is not. The eaves limit applies to the part that is, which means the eaves line may need to step or slope. A mono-pitch roof falling towards the boundary handles this well, provided the low edge still gives a usable ceiling inside.
Where the boundary is defined by a hedge, the legal line is often not the centre of the hedge, and assuming it is can cost half a metre. Where the boundary is disputed or undefined, resolve it before you build. An extension built on an assumption about a boundary is the sort of thing that surfaces during a sale two years later.
Corner plots need particular care, because a side boundary with a road frontage can be much closer than it looks once the highway boundary is properly established.
How schemes break the rule
The failures repeat. Six of them cover nearly everything.
A pitched roof designed for the middle of the extension, with the eaves carried through to a section within two metres of the boundary. A floor build-up added after the planning check, pushing the wall plate above three metres. Sloping ground measured at the high end only. A parapet or plant screen added at detail design. A boundary assumed from the title plan rather than surveyed. And an extension measured to the wall face when a projecting element sits closer.
The best insurance is a dimensioned section through the worst point, drawn early, showing the finished floor level, the ground level, the eaves and the boundary distance on one drawing. It takes twenty minutes.
Where the design cannot work within the limits, a householder planning application is the straightforward alternative, and councils frequently permit eaves above three metres close to a boundary where the effect on the neighbour is acceptable. A short Planning Statement setting out the daylight and outlook position for the neighbour is often what tips such an application.
Designing to the limit with a margin
Build tolerance in, because the tolerance is the difference between permitted development and a breach.
- Survey the boundary and the ground levels before drawing anything.
- Establish the curtilage line where any part of the plot may sit outside it.
- Draw a dimensioned section at the closest point to the boundary, at the lowest ground level.
- Design the eaves to about 2.85 metres rather than 2.99 metres, so the build-up does not take you over.
- Keep parapets, upstands and screens clear of the section within two metres of the boundary.
- Check the other Class A limits at the same time, including the four metre overall height and the existing eaves height.
- Consider a lawful development certificate under section 192 of the Town and Country Planning Act 1990 where the margin is tight.
The last point is worth more than it costs. A certificate gives a binding answer, and it is the document a buyer's solicitor will ask for. Other Class A limits interact with equipment on the roof, and our note on the 200 millimetre projection limit for domestic solar panels covers one of them. Where rights have been withdrawn entirely, none of the limits matter, and our note on Article 4 directions and the move between C3 and C4 explains how such directions operate.
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Frequently asked questions
Does the three metre eaves limit apply to the whole extension?
Only to the part within two metres of the boundary of the curtilage. An extension can step in or slope so that the section nearest the boundary has eaves below three metres while a section further away is taller, provided the other Class A height limits are also met, including the four metre overall limit for a single-storey rear extension.
Which boundary does the two metres apply to?
Any boundary of the curtilage of the dwellinghouse, including side boundaries with neighbours, the rear boundary and the boundary with a road or footpath. A rear extension across a narrow garden can easily be within two metres of the rear boundary, which engages the rule even where no neighbour is affected.
How is eaves height measured on sloping ground?
Height is measured from ground level, and where the ground is not uniform the Order and the government's technical guidance direct the measurement to a defined point. Take levels along the whole wall within two metres of the boundary and check the worst case. Where the margin is small, get the authority's view in writing.
Does a parapet count towards eaves height?
For a flat roof the eaves height is effectively the wall height where the roof meets it, and a parapet above that adds to the overall height of the extension. Councils read this detail differently, so on a scheme designed to the limit it is worth a written query rather than an assumption about how it will be measured.
What happens if the extension exceeds three metres to the eaves?
It is no longer permitted development, so it becomes unauthorised development requiring a planning application or, if already built, a retrospective application or a certificate of lawfulness. A householder application is often granted for higher eaves near a boundary where the effect on the neighbour is acceptable, so the practical answer is usually to apply.
Sources and further reading
This article is general guidance about the planning system in England and, where stated, the rest of the UK. It is not legal or professional advice. Check your local planning authority’s validation requirements and take professional advice for your specific site.