Single-storey, double-storey, rear and side extension drawings for Letchworth South West homes — measured to North Hertfordshire District Council's design guidance, delivered in days and revised free until your decision, with a free approval-odds check before you commit.
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. Letchworth South West contains Letchworth, Willian conservation areas (Letchworth designated 1974), so materials, fenestration and roof form are assessed against the appraisal, which is where a policy-literate drawing pack earns its keep. Its dominant Edwardian (1901–1910) and interwar (1918–1939) 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 Letchworth and Willian those rights are removed, so we confirm your exact address before a line is drawn. A validated householder application in Letchworth South West is determined against an 8-week statutory target.
Letchworth (conservation area designated in 1974) and Willian (conservation area designated in 1973) — these are the Letchworth South West pockets our drawings cover most. Heritage designations here include Letchworth and Willian. North Hertfordshire District Council weighs each proposal against North Hertfordshire District Council's development plan and the design policies it applies to householder applications, where the 3,680 homes here are 21% 1919-1929, 17% 1973-1982, 15% 1900-1918, which is what sets the realistic roof and rear-projection options. On roofs the borough is hipped tiled roofs typical of early interwar building and shallow trussed roofs typical of 1970s building, over early interwar houses (21% of 3,680 homes), 1970s and early-1980s houses (17%) and Edwardian houses (15%).
Heritage designation is the single biggest variable in Letchworth South West, and it is address-specific: Letchworth (conservation area designated in 1974) and Willian (conservation area designated in 1973). 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.
No Article 4 direction is recorded for North Hertfordshire District Council, but Letchworth South West's 2 conservation areas still limit permitted development on those streets.
On stock, Letchworth South West is early interwar houses (21% of 3,680 homes), 1970s and early-1980s houses (17%) and Edwardian houses (15%) — which is why hipped tiled roofs typical of early interwar building and shallow trussed roofs typical of 1970s 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 Letchworth South West runs pre-1900 3% (110 homes), 1900-1918 15% (540 homes), 1919-1929 21% (760 homes), 1930-1939 3% (110 homes), 1945-1954 2% (70 homes), 1955-1964 7% (260 homes), 1965-1972 9% (330 homes), 1973-1982 17% (620 homes), 1983-1992 10% (380 homes), 1993-1999 2% (60 homes) and 2000-2008 4% (160 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 Letchworth South West 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 Letchworth South West 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 | Letchworth South West |
|---|---|
| Dwellings recorded | 3,680 |
| Built pre-1900 | 110 (3%) |
| Built 1900-1918 | 540 (15%) |
| Built 1919-1929 | 760 (21%) |
| Built 1930-1939 | 110 (3%) |
| Built 1945-1954 | 70 (2%) |
| Built 1955-1964 | 260 (7%) |
| Built 1965-1972 | 330 (9%) |
| Built 1973-1982 | 620 (17%) |
| Built 1983-1992 | 380 (10%) |
| Built 1993-1999 | 60 (2%) |
| Built 2000-2008 | 160 (4%) |
| Built before 1919 | 18% |
| Built 1919–1939 | 24% |
| Built 1945–2008 | 51% |
| Conservation areas in Letchworth South West | 2 (Letchworth, Willian) |
| 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.
Letchworth South West homes come in a handful of recurring shapes, and each one points to a different extension. The borough is built largely from early interwar houses (21% of 3,680 homes), 1970s and early-1980s houses (17%) and Edwardian houses (15%), so a Victorian terrace usually wants a rear or side-return infill, while an interwar semi has room for a wider single-storey wrap or a two-storey side addition. North Hertfordshire District Council judges every one of them against North Hertfordshire District Council's development plan and the design policies it applies to householder applications, weighing footprint, height and the impact on the house next door before it looks at the elevations.
That is why the drawings decide the outcome. We set the extension depth against the permitted-development limits precisely, keep the eaves and ridge within the allowances, and plot the 45-degree daylight lines to the neighbours' windows so the case officer can see the amenity test is passed. Letchworth South West contains Letchworth, Willian conservation areas (Letchworth designated 1974), so materials, fenestration and roof form are assessed against the appraisal, so we design around it from the first sketch rather than discover it at validation.
Letchworth South West also protects whole streets — Letchworth and Willian among them. No Article 4 direction is recorded for North Hertfordshire District Council, but Letchworth South West's 2 conservation areas still limit permitted development on those streets. On designated land the larger-home extension route and most side extensions stop being permitted development, so we confirm your address against those layers before drawing a line.
Plenty of Letchworth South West extensions are permitted development and need no planning application — a single-storey rear extension within the depth and height limits is the common case. You will normally need to apply to North Hertfordshire District Council if any of these apply:
We draw the footprint, the ridge and eaves heights and the neighbours' daylight on the page — the relationships North Hertfordshire District Council's officers weigh first — and submit a validation-complete pack, whether that is a lawful development certificate, a prior-approval notification or a full householder application.
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 Letchworth shapes what is approved here. A complete, policy-literate extension pack anticipates those pressure points before submission, which is why professionally drawn applications are decided faster and refused less often than DIY ones.
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 Letchworth and Willian, the extension that lands most often is the single-storey rear addition — a glazed kitchen-diner across the back of the house, kept within the permitted-development depth or taken to a full application where the ground floor wants more. On the borough's early interwar houses (21% of 3,680 homes), a side-return infill frequently pairs with it to square off the plan; on wider edwardian houses (15%), a two-storey side or rear extension can add a bedroom above without swallowing the garden.
The 3,680 homes here are 21% 1919-1929, 17% 1973-1982, 15% 1900-1918, which is what sets the realistic roof and rear-projection options. We size the extension to the amenity and daylight tests, match the roof and materials to the host house, and keep enough garden to satisfy North Hertfordshire District Council's space standards — so the scheme answers the borough's questions before an objection can raise them. Where permitted-development rights are used up or removed, we prepare the householder application to the council's extension design guidance instead.
We draw extensions on every street in the borough. A few of the neighbourhoods where Letchworth South West projects come up most often:
Extension drawings for Letchworth's conservation area designated in 1974 — footprint-checked, daylight-tested and drawn to North Hertfordshire District Council's guidance.
Extension drawings for Willian's conservation area designated in 1973 — footprint-checked, daylight-tested and drawn to North Hertfordshire District Council's guidance.
The right extension in Letchworth South West depends on your house type and how much garden you can give up. This is how the main options compare on planning route and what they add.
| Extension type | Permitted development? | What it adds | What North Hertfordshire District Council checks |
|---|---|---|---|
| Single-storey rear | Often, within 3m/4m depth (6m/8m via prior approval) | Bigger kitchen-diner across the back | Depth, height, neighbour daylight (45°) |
| Side-return infill | Sometimes, if within width and height limits | Squares off an L-shaped ground floor | Width vs the original house, glazing to boundary |
| Two-storey rear/side | No — full application | Extra bedroom or bathroom above | Bulk, overlooking, 7m rear-boundary gap |
| Wraparound (rear + side) | No — full application | Whole-width open-plan ground floor | Combined footprint and garden retained |
Route depends on your street — conservation areas such as Letchworth and Willian and Article 4 directions can remove permitted-development rights.
A fixed process built around how North Hertfordshire District Council validates and decides householder extension applications — most drawings are submission-ready within seven days of survey.
Tell us your Letchworth South West postcode and house type. We confirm your conservation and Article 4 status, how much permitted-development depth you have left, and score your odds against live North Hertfordshire District Council decisions.
We measure the existing footprint, floor and eaves levels, boundary distances and the neighbours' window positions — the numbers the depth limits and daylight tests depend on.
Chartered designers develop the single-storey, two-storey or side extension to your brief, drawn inside the permitted-development limits or to North Hertfordshire District Council's extension design guidance.
We submit the certificate, prior-approval notice or application, manage validation and case-officer queries, and revise the drawings free until North Hertfordshire District Council issues its decision.
Not always. A single-storey rear extension up to 3 metres deep on a terrace or semi, or 4 metres on a detached house, and no higher than 4 metres, is usually permitted development. In Letchworth South West you will need to apply to North Hertfordshire District Council for two-storey extensions, side extensions wider than half the house, anything forward of the front wall, deeper rear extensions under the larger-home prior-approval route, and any extension in a conservation area such as Letchworth and Willian.
Standard permitted development allows 3 metres on a terraced or semi-detached house and 4 metres on a detached one. The larger-home extension scheme can double that to 6 or 8 metres, but it needs a prior-approval notification to North Hertfordshire District Council and a neighbour-consultation period, and it does not apply on designated land such as Letchworth South West's conservation areas. We confirm which route your property qualifies for before drawing.
Two-storey and double-storey extensions almost always need a full householder application to North Hertfordshire District Council, because they fall outside permitted development on most homes. The council looks closely at bulk, overlooking of neighbours and the 7-metre gap a two-storey rear extension must keep from the rear boundary. We design to those tests and show the daylight and privacy angles on the drawings. This applies to your Letchworth South West address specifically.
A householder planning application in Letchworth South West runs to a statutory eight-week target, a larger-home prior-approval notification to around six weeks including the neighbour-consultation period, and a lawful development certificate to eight weeks. Incomplete submissions stall at validation, so we submit a complete pack and manage officer queries to keep the decision on schedule. North Hertfordshire District Council is the decision-maker.
Yes — planning permission and building regulations are separate consents, and almost every extension needs both. Planning governs whether you can build it; building control governs how it is built, covering structure, insulation, drainage and fire safety. We prepare the building-regulations drawings alongside the planning set so North Hertfordshire District Council's building control or an approved inspector can sign the work off. This applies to your Letchworth South West address specifically.
Every house and brief is different, so we price each Letchworth South West extension individually and send a fixed, no-obligation quote back within one working day. It covers the full drawing pack with free revisions until North Hertfordshire District Council approves, and we tell you upfront whether your extension qualifies as permitted development. Call 020 7864 7245 to get started.
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