Rear dormer drawings for Hertsmere roofs — the box across the back slope that turns a low attic into a full-height room, drawn to Hertsmere Borough Council's guidance and the volume limits, delivered in days and revised free until your decision, with a free approval-odds check first.
Hertsmere Borough Council granted 94% of the householder planning decisions it made in its latest published year — 7 points above the 87% England-wide householder average. Hertsmere contains Aldenham, Bushey Heath High Road, Bushey Heath The Lake conservation areas (Aldenham designated 1973), so materials, fenestration and roof form are assessed against the appraisal, which is where a policy-literate drawing pack earns its keep. Its dominant postwar (1945–1970) housing stock sets the design brief on most streets.
Before permission is required, Class B allows 40m³ of added loft volume on a terrace and 50m³ on a semi or detached house, and Class A allows a 3m single-storey rear extension on a terrace or 4m on a detached house. In conservation areas such as Aldenham, Bushey Heath High Road and Bushey Heath The Lake those rights are removed, so we confirm your exact address before a line is drawn. A validated householder application in Hertsmere is determined against an 8-week statutory target.
Aldenham (conservation area designated in 1973), Bushey Heath High Road (conservation area designated in 1990), Bushey Heath The Lake (conservation area designated in 1998), Bushey High Street (conservation area designated in 1973), Bushey Melbourne Road (conservation area designated in 1973), Elstree Village (conservation area designated in 1976), Letchmore Heath (conservation area designated in 1969), Patchetts Green and Delrow (conservation area designated in 1998), Aldenham East (ward of Hertsmere), Aldenham West (ward of Hertsmere), Bushey Heath (ward of Hertsmere), Bushey St James (ward of Hertsmere), Elstree (ward of Hertsmere) and Shenley (ward of Hertsmere) — these are the Hertsmere pockets our drawings cover most. Heritage designations here include Aldenham, Bushey Heath High Road, Bushey Heath The Lake, Bushey High Street, Bushey Melbourne Road, Elstree Village, Letchmore Heath and Patchetts Green and Delrow. Hertsmere Borough Council weighs each proposal against the adopted Hertsmere local plan and Hertsmere Borough Council's design guidance for householder work, where the 13,370 homes here are 15% 1955-1964, 8% 1965-1972, 7% 1993-1999, which is what sets the realistic roof and rear-projection options. On roofs the borough is shallow gabled roofs typical of that period's building and shallow-pitched roofs and integral garages typical of that period's building, over late-1950s and early-1960s houses (15% of 13,370 homes), late-1960s and early-1970s houses (8%) and 1990s estate houses (7%).
What is permitted in Hertsmere turns on designation first, so that is where we start: Aldenham (conservation area designated in 1973), Bushey Heath High Road (conservation area designated in 1990), Bushey Heath The Lake (conservation area designated in 1998), Bushey High Street (conservation area designated in 1973), Bushey Melbourne Road (conservation area designated in 1973), Elstree Village (conservation area designated in 1976), Letchmore Heath (conservation area designated in 1969) and Patchetts Green and Delrow (conservation area designated in 1998). Inside those boundaries permitted development is curtailed and Hertsmere Borough 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, Hertsmere takes in Aldenham East, Aldenham West, Bushey Heath, Bushey St James, Elstree and Shenley. No Article 4 direction is recorded for Hertsmere Borough Council, but the district's 8 conservation areas still limit permitted development on those streets.
On stock, Hertsmere is late-1950s and early-1960s houses (15% of 13,370 homes), late-1960s and early-1970s houses (8%) and 1990s estate houses (7%) — which is why shallow gabled roofs typical of that period's building and shallow-pitched roofs and integral garages typical of that period's building govern what a loft or rear projection can realistically be. Hertsmere Borough Council decided 466 householder applications in the latest published year and granted 94%, with 49% issued inside the eight-week target. We draw to that record rather than to a national average.
The full build-period split for Hertsmere runs pre-1900 3% (190 homes), 1900-1918 0% (30 homes), 1919-1929 0% (10 homes), 1930-1939 6% (350 homes), 1945-1954 3% (170 homes), 1955-1964 30% (1,850 homes), 1965-1972 33% (1,990 homes), 1973-1982 4% (260 homes), 1983-1992 5% (310 homes), 1993-1999 4% (220 homes) and 2000-2008 3% (170 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.
Hertsmere Borough Council also decides for Aldenham East, Aldenham West, Bushey Heath, Bushey St James, Elstree and Shenley, so a decision in Hertsmere 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 Hertsmere and Hertsmere Borough Council. These are the numbers that decide what is realistic on your street, so we work from them rather than from national averages.
| Measure | Hertsmere |
|---|---|
| Dwellings recorded | 13,370 |
| Built pre-1900 | 190 (3%) |
| Built 1900-1918 | 30 (0%) |
| Built 1919-1929 | 10 (0%) |
| Built 1930-1939 | 350 (6%) |
| Built 1945-1954 | 170 (3%) |
| Built 1955-1964 | 1,850 (30%) |
| Built 1965-1972 | 1,990 (33%) |
| Built 1973-1982 | 260 (4%) |
| Built 1983-1992 | 310 (5%) |
| Built 1993-1999 | 220 (4%) |
| Built 2000-2008 | 170 (3%) |
| Built before 1919 | 13% |
| Built 1919–1939 | 14% |
| Built 1945–2008 | 60% |
| Conservation areas in Hertsmere | 8 (Aldenham, Bushey Heath High Road…) |
| Conservation areas district-wide | 16 |
| Article 4 directions recorded | 0 |
| Householder applications decided | 466 |
| Householder applications granted | 94% |
| Decided within 8 weeks | 49% |
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 Hertsmere Borough Council's own, from MHCLG live table PS2 for the year to 31 March 2026.
The box dormer is the workhorse loft, and most of Hertsmere is built for it — the borough runs to late-1950s and early-1960s houses (15% of 13,370 homes), late-1960s and early-1970s houses (8%) and 1990s estate houses (7%) under shallow gabled roofs typical of that period's building and shallow-pitched roofs and integral garages typical of that period's building, and a flat-roofed box across the rear slope is the cheapest cubic metre of full-height space those roofs give up. Hertsmere Borough Council tests the dormer against the adopted Hertsmere local plan and Hertsmere Borough Council's design guidance for householder work, and because permitted development turns on a number, the volume you propose against the volume you have left is the first thing an officer or a certificate checks.
That is why the arithmetic goes on the drawings. We calculate the box against the 40- or 50-cubic-metre allowance, count any earlier roof enlargement into the total, hold the flat roof below the ridge and set the face back off the eaves so the dormer reads as subordinate. Hertsmere contains Aldenham, Bushey Heath High Road, Bushey Heath The Lake conservation areas (Aldenham designated 1973), so materials, fenestration and roof form are assessed against the appraisal, so the cheeks, the window line and the material are drawn to answer it rather than invite a query.
Where Hertsmere's streets are protected — Aldenham, Bushey Heath High Road, Bushey Heath The Lake, Bushey High Street, Bushey Melbourne Road, Elstree Village, Letchmore Heath and Patchetts Green and Delrow among them — the Class B dormer right is switched off and even a modest rear box needs consent. No Article 4 direction is recorded for Hertsmere Borough Council, but the district's 8 conservation areas still limit permitted development on those streets. We confirm the designation before the box is sized.
Many rear dormers in Hertsmere are permitted development, but the volume and position decide it. You will normally need a full application to Hertsmere Borough Council if any of these apply:
We draw the box within its volume allowance, the flat roof below the ridge and the face set back off the eaves — the three things a dormer stands or falls on — and submit a validation-complete pack, whether that is a lawful development certificate or a full householder application.
Below is Hertsmere Borough Council's real householder decision record, drawn from official planning statistics and refreshed as new data lands. Hertsmere Borough Council granted 94% of 466 householder decisions in the year to 31 March 2026, 49% of them inside eight weeks. A dormer is decided on volume and set-back, so a pack that shows the calculation and the eaves detail is cleared faster and refused less often than a DIY submission.
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 Aldenham, Bushey Heath High Road and Bushey Heath The Lake, the dormer that goes through is the subordinate rear box: flat roof kept low, cheeks clad to recede, side windows obscure-glazed against overlooking, and the whole thing set back so the original eaves line still reads from the garden. On shallow gabled roofs typical of that period's building, this returns a full-height double and en-suite from what was standing-room-only, usually inside the permitted-development volume.
The 13,370 homes here are 15% 1955-1964, 8% 1965-1972, 7% 1993-1999, which is what sets the realistic roof and rear-projection options. We keep the box off the ridge, match the cheek material to the roof, and where the volume is already spent — or the street is designated — draw the dormer as a householder application composed to Hertsmere Borough Council's roof-alteration guidance rather than push a certificate that would be refused.
We draw rear dormers on the terraced and semi-detached streets across the borough. A few of the neighbourhoods where Hertsmere dormers come up most often:
Dormer loft drawings for Aldenham's conservation area designated in 1973 — volume-checked, set-back-detailed and drawn to Hertsmere Borough Council's guidance.
Dormer loft drawings for Bushey Heath High Road's conservation area designated in 1990 — volume-checked, set-back-detailed and drawn to Hertsmere Borough Council's guidance.
Dormer loft drawings for Bushey Heath The Lake's conservation area designated in 1998 — volume-checked, set-back-detailed and drawn to Hertsmere Borough Council's guidance.
Dormer loft drawings for Bushey High Street's conservation area designated in 1973 — volume-checked, set-back-detailed and drawn to Hertsmere Borough Council's guidance.
Dormer loft drawings for Bushey Melbourne Road's conservation area designated in 1973 — volume-checked, set-back-detailed and drawn to Hertsmere Borough Council's guidance.
Dormer loft drawings for Elstree Village's conservation area designated in 1976 — volume-checked, set-back-detailed and drawn to Hertsmere Borough Council's guidance.
Whether a dormer in Hertsmere needs permission comes down to where it sits and how big the box is. This is how the cases compare.
| Dormer type | Permitted development? | What it gains | What Hertsmere Borough Council checks |
|---|---|---|---|
| Rear box, within volume | Usually yes | Full-height room across the back | Volume total, 20cm eaves set-back |
| Rear box, over volume limit | No — full application | A larger room | How far over the allowance, bulk |
| Front or side dormer | No — full application | Light to the front rooms | Visibility from the street, character |
| Dormer in a conservation area | No — full application | Same space, extra scrutiny | Roof form and street appearance |
In conservation areas such as Aldenham and Bushey Heath High Road, Class B dormer rights are removed and every dormer needs a full application.
A fixed process built around how Hertsmere Borough Council validates and decides dormer applications — most drawings are submission-ready within seven days of survey.
Send us your Hertsmere postcode and roof type. We confirm your conservation and Article 4 status, work out how much permitted-development volume you have left, and score your odds against live Hertsmere Borough Council decisions.
We measure ridge and eaves heights, roof pitch and the existing loft floor — the numbers the volume calculation, the set-back and the head heights depend on.
Chartered designers develop the box to your brief, drawn inside the Class B volume limits or, where those are exhausted or removed, to Hertsmere Borough Council's roof-alteration guidance.
We submit the certificate or application, manage validation and case-officer queries, and revise the drawings free until Hertsmere Borough Council issues its decision.
Often not. A rear box dormer within 40 cubic metres on a terrace, or 50 on a semi or detached house, set back at least 20 centimetres from the eaves and kept below the ridge, is usually permitted development. In Hertsmere you will need a full application to Hertsmere Borough Council for a front or side dormer, a box that exceeds the volume, and any dormer in a conservation area such as Aldenham and Bushey Heath High Road, where those rights are removed.
The permitted-development limit is a volume, not a footprint: 40 cubic metres of added roof space on a terraced house and 50 on a semi-detached or detached one, and any earlier loft enlargement counts against that total. In Hertsmere the box must also sit below the ridge and back from the eaves. We measure your roof and calculate the exact volume you have left before drawing. Hertsmere Borough Council is the decision-maker.
Not under permitted development. A dormer on the front roof slope, or one facing a highway, always needs a full application to Hertsmere Borough Council, because it changes how the house reads from the street. Rear box dormers are far more likely to be approved — or to be permitted development outright — which is why almost every Hertsmere dormer we draw sits on the back slope.
Often, on a terrace or semi. If the dormer or the loft steelwork meets the party wall with your neighbour, the Party Wall etc. Act applies and notice must be served before work starts — separately from Hertsmere Borough Council's planning decision. We flag the party-wall junction on the drawings so a surveyor can be appointed early and the build is not held up.
If your dormer is permitted development, a lawful development certificate from Hertsmere Borough Council is council-stamped proof of it — worth holding, because a buyer's solicitor will ask for it when you sell. We prepare and submit the certificate with the same measured drawing pack that shows the box within its volume allowance.
We price each Hertsmere dormer individually, because the roof pitch and the volume left vary house to house, and send a fixed, no-obligation quote within one working day. It covers the full drawing pack with free revisions until Hertsmere Borough Council approves, and we confirm at the outset whether your box is permitted development or needs an application. Call 020 7864 7245 to start.
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