The fast route to a deep single-storey rear extension in Offa — up to 6 metres on an attached house or 8 on a detached one — via North Hertfordshire District Council's prior approval scheme rather than a full planning application.
North Hertfordshire District Council granted 95% of the householder planning decisions it made in its latest published year — 8 points above the 87% England-wide householder average. Offa contains Great Offley, Hexton, Lilley conservation areas (Great Offley designated 1969), so materials, fenestration and roof form are assessed against the appraisal, which is where a policy-literate drawing pack earns its keep. Its dominant Victorian (1837–1901), interwar (1918–1939) and postwar (1945–1970) housing stock sets the design brief on most streets.
Class A and Class B set the thresholds — a rear dormer to 40m³ on a terrace or 50m³ on a semi or detached, and a single-storey rear extension to 3m on a terrace or 4m on a detached house — beyond which North Hertfordshire District Council needs a full application. In conservation areas such as Great Offley, Hexton and Lilley those rights are removed, so we confirm your exact address before a line is drawn. A validated householder application in Offa is determined against an 8-week statutory target.
Great Offley (conservation area designated in 1969), Hexton (conservation area designated in 1975), Lilley (conservation area designated in 1979), Pirton (conservation area designated in 1969), Shillington (Aspley End) (designated conservation area), Hexton (civil parish within Offa), Lilley (civil parish within Offa), Offley (civil parish within Offa) and Pirton (civil parish within Offa) — these are the Offa pockets our drawings cover most. Heritage designations here include Great Offley, Hexton, Lilley, Pirton and Shillington (Aspley End) Conservation Area. North Hertfordshire District Council weighs each proposal against the adopted North Hertfordshire local plan and North Hertfordshire District Council's design guidance for householder work, where the 1,710 homes here are 23% pre-1900, 11% 1919-1929, 11% 1955-1964, which is what sets the realistic roof and rear-projection options. On roofs the borough is steeply pitched slate roofs, valley gutters and party parapets typical of pre-1900 building and hipped tiled roofs typical of early interwar building, over Victorian and earlier houses (23% of 1,710 homes), early interwar houses (11%) and late-1950s and early-1960s houses (11%).
Heritage designation is the single biggest variable in Offa, and it is address-specific: Great Offley (conservation area designated in 1969), Hexton (conservation area designated in 1975), Lilley (conservation area designated in 1979), Pirton (conservation area designated in 1969) and Shillington (Aspley End) (designated conservation area). Inside those boundaries permitted development is curtailed and North Hertfordshire District Council assesses materials, window detail and roof form against the area's own appraisal, so a scheme that would be waved through two streets away can need a full application here.
Beyond the designated areas, Offa takes in Hexton, Lilley, Offley and Pirton. No Article 4 direction is recorded for North Hertfordshire District Council, but Offa's 5 conservation areas still limit permitted development on those streets.
On stock, Offa is Victorian and earlier houses (23% of 1,710 homes), early interwar houses (11%) and late-1950s and early-1960s houses (11%) — which is why steeply pitched slate roofs, valley gutters and party parapets typical of pre-1900 building and hipped tiled roofs typical of early interwar building govern what a loft or rear projection can realistically be. North Hertfordshire District Council decided 665 householder applications in the latest published year and granted 95%, with 69% issued inside the eight-week target. We work from the council's own published record.
The full build-period split for Offa runs pre-1900 23% (400 homes), 1900-1918 2% (40 homes), 1919-1929 11% (190 homes), 1930-1939 4% (70 homes), 1945-1954 9% (160 homes), 1955-1964 11% (190 homes), 1965-1972 9% (160 homes), 1973-1982 4% (60 homes), 1983-1992 4% (60 homes), 1993-1999 2% (40 homes) and 2000-2008 4% (70 homes). That distribution is why pre-1900 detailing dominates the drawings here, and it is measured from council-tax records rather than assumed from the street name.
North Hertfordshire District Council also decides for Arbury, Baldock West, Cadwell, Codicote & Kimpton, Ermine, Hitchin Priory, Hitchwood and Knebworth, so a decision in Offa sits inside a wider pattern of decisions we track across the same authority — useful when an officer cites a precedent from the next area over.
Published figures for Offa and North Hertfordshire District Council. These are the numbers that decide what is realistic on your street, so we work from them rather than from national averages.
| Measure | Offa |
|---|---|
| Dwellings recorded | 1,710 |
| Built pre-1900 | 400 (23%) |
| Built 1900-1918 | 40 (2%) |
| Built 1919-1929 | 190 (11%) |
| Built 1930-1939 | 70 (4%) |
| Built 1945-1954 | 160 (9%) |
| Built 1955-1964 | 190 (11%) |
| Built 1965-1972 | 160 (9%) |
| Built 1973-1982 | 60 (4%) |
| Built 1983-1992 | 60 (4%) |
| Built 1993-1999 | 40 (2%) |
| Built 2000-2008 | 70 (4%) |
| Built before 1919 | 26% |
| Built 1919–1939 | 15% |
| Built 1945–2008 | 43% |
| Conservation areas in Offa | 5 (Great Offley, Hexton…) |
| Conservation areas district-wide | 44 |
| Article 4 directions recorded | 0 |
| Householder applications decided | 665 |
| Householder applications granted | 95% |
| Decided within 8 weeks | 69% |
Dwelling stock from VOA council-tax data at 31 March 2025; conservation-area and Article 4 counts from planning.data.gov.uk (MHCLG); decision figures are North Hertfordshire District Council's own, from MHCLG live table PS2 for the year to 31 March 2026.
The ordinary Class A limits stop a single-storey rear extension at 3 metres on an attached house and 4 on a detached one. The larger home extension scheme doubles both, on condition that the council is told first. That notification is not an application for permission — the council cannot refuse on design, materials or policy grounds. It can only consider the effect on the amenity of adjoining premises, and only if a neighbour actually objects during the 21-day consultation.
The other conditions still apply and are strict: single storey only, no higher than 4 metres, eaves no higher than the existing eaves, and no more than half the land around the original house covered. It is not available on designated land, so a house in a conservation area such as Great Offley and Hexton cannot use it at all. Materials must be similar to the existing house, and the extension must not include a veranda, balcony or raised platform.
Offa is largely Victorian and earlier houses (23% of 1,710 homes), early interwar houses (11%) and late-1950s and early-1960s houses (11%). Offa contains Great Offley, Hexton, Lilley conservation areas (Great Offley designated 1969), so materials, fenestration and roof form are assessed against the appraisal, which matters here because an objecting neighbour puts amenity squarely in front of a case officer. No Article 4 direction is recorded for North Hertfordshire District Council, but Offa's 5 conservation areas still limit permitted development on those streets.
The scheme is available where all of these hold. Fail any one and it is a full application to North Hertfordshire District Council instead:
We prepare the notification pack North Hertfordshire District Council needs — plans, elevations, a site plan with the adjoining owners identified — and manage the 21-day neighbour consultation so the 42-day clock is not restarted by an incomplete submission.
Below is North Hertfordshire District Council's real householder decision record, drawn from official planning statistics and refreshed as new data lands. North Hertfordshire District Council granted 95% of its householder applications in the year to 31 March 2026, and Great Offley shapes what is approved here. Prior approval turns on neighbour amenity alone, so the drawings that matter are the ones showing the relationship to the boundary.
Source: MHCLG planning application statistics (householder decisions, England, 1 April 2025 - 31 March 2026). Compare every borough on our London approval-rate league table.
Tell us about your project and get a fixed, no-obligation quote back within one working day. If you don't need planning permission at all, we'll tell you that too — for free.
Across Great Offley, Hexton and Lilley, the notifications that clear without objection are the ones that treat the neighbour as the audience. We show the extension in section against the boundary, demonstrate the 45-degree daylight relationship to the nearest habitable window, and where the plot is tight we taper the depth away from the boundary rather than running the full 6 metres to the fence.
The 1,710 homes here are 23% pre-1900, 11% 1919-1929, 11% 1955-1964, which is what sets the realistic roof and rear-projection options. Where an objection does arrive, the council's assessment is narrow: loss of light, outlook and overbearing effect on the adjoining property, nothing else. A pack that has already answered those three points on the drawings usually survives an objection, whereas one that leaves them to the officer's imagination usually does not.
We prepare prior-approval notifications across Offa. A few of the areas where deep rear extensions come up most often:
Prior approval drawings for Great Offley — conservation area designated in 1969 — dimensioned to the 6m and 8m limits and prepared for North Hertfordshire District Council's neighbour consultation.
Prior approval drawings for Hexton — conservation area designated in 1975 — dimensioned to the 6m and 8m limits and prepared for North Hertfordshire District Council's neighbour consultation.
Prior approval drawings for Lilley — conservation area designated in 1979 — dimensioned to the 6m and 8m limits and prepared for North Hertfordshire District Council's neighbour consultation.
Prior approval drawings for Pirton — conservation area designated in 1969 — dimensioned to the 6m and 8m limits and prepared for North Hertfordshire District Council's neighbour consultation.
Prior approval drawings for Shillington (Aspley End) — designated conservation area — dimensioned to the 6m and 8m limits and prepared for North Hertfordshire District Council's neighbour consultation.
Prior approval drawings for Hexton — civil parish within Offa — dimensioned to the 6m and 8m limits and prepared for North Hertfordshire District Council's neighbour consultation.
Same extension, two routes, very different tests.
| Route | Depth allowed | What the council may consider | Timescale |
|---|---|---|---|
| Ordinary Class A permitted development | 3m attached / 4m detached | Nothing — no application needed | Immediate |
| Larger home extension prior approval | 6m attached / 8m detached | Amenity of adjoining premises, only if a neighbour objects | 21-day consultation, 42-day determination |
| Full householder application | No fixed limit | Design, materials, policy, amenity, everything | 8-week target |
| Any of these on designated land | 3m / 4m only | Prior approval scheme unavailable | Full application beyond the limits |
Limits and procedure from the GPDO 2015, Schedule 2, Part 1, Class A and paragraph A.4, made permanent by amendment in 2019.
A process built around the 21-day consultation, which is where these schemes are won or lost.
Send us your Offa postcode and house type. We confirm whether the property is on designated land, whether the scheme is available, and what depth you can realistically take.
We measure the original rear wall, eaves height, boundary distances and the neighbouring windows that the amenity assessment will turn on.
We draw the extension to the 6m or 8m limit with the boundary relationship shown in section, and prepare the written description and adjoining-owner details North Hertfordshire District Council needs to start the consultation.
We submit, track the 21-day consultation and the 42-day determination, respond to any objection on amenity grounds, and revise free until the decision.
Three metres on a terraced or semi-detached house and four on a detached one under ordinary permitted development. Under the larger home extension prior approval scheme those double to six and eight metres, provided you notify North Hertfordshire District Council before starting and the conditions on height, materials and land coverage are met. The scheme is not available on designated land. This applies to your Offa address specifically.
It is a notification, not an application for permission. You tell North Hertfordshire District Council what you intend to build, it writes to the adjoining owners, and they have 21 days to object. If nobody objects, you may build. If someone does, the council assesses the effect on the amenity of adjoining premises and must decide within 42 days. Design and policy are not in scope. This applies to your Offa address specifically.
The council then considers the impact on the amenity of the adjoining property — loss of light, loss of outlook, and overbearing effect — and nothing else. It cannot refuse because it dislikes the design or the materials. We prepare the drawings so those three questions are already answered in section and on the site plan, which is what usually carries an objected scheme through. This applies to your Offa address specifically. North Hertfordshire District Council is the decision-maker.
No. The larger home extension scheme is unavailable on designated land, which includes conservation areas such as Great Offley and Hexton, national landscapes, national parks and world heritage sites. On those properties the ordinary 3-metre and 4-metre limits apply, and anything deeper needs a full householder application to North Hertfordshire District Council. This applies to your Offa address specifically.
Twenty-one days for the neighbour consultation, and a maximum of 42 days from a valid submission for the council to determine it. If the council does not respond within 42 days you may proceed as notified. That deadline is the scheme's real advantage over a full application, and it is why validation completeness matters so much. This applies to your Offa address specifically. North Hertfordshire District Council is the decision-maker.
Yes — always. Prior approval deals only with the planning position. A 6-metre rear extension still needs building control approval for foundations, structure, drainage, thermal performance and fire safety, and the beam over the opening into the existing house needs designing and calculating. We prepare both sets so the notified scheme is the buildable one. This applies to your Offa address specifically. North Hertfordshire District Council is the decision-maker.
We quote each Offa scheme individually, because plot shape and the boundary relationship drive the work, and send a fixed, no-obligation quote within one working day. It covers the notification pack and free revisions until North Hertfordshire District Council determines it. Call 020 7864 7245 to start.
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Same fixed quotes, same fast drawings — wherever your project is.