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Free 2026 London Planning Report — Rear Extension Drawings in Sidcup DA15

Kitchen extension interior in a 1930s Sidcup DA15 semi, London Borough of Bexley
Sidcup · DA15 · Bexley

Rear Extension Drawings in Sidcup DA15

Fixed-fee, MCIAT-chartered rear extension drawings for Sidcup (DA15) homeowners — London Borough of Bexley validation and local constraints handled from the start.

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Sidcup's DA15 stretches north and west from the town toward Blackfen, Lamorbey and Longlands, mixing broad inter-war suburban avenues with older hamlets along Halfway Street and Burnt Oak Lane. Side-return, rear and loft extensions on the 1930s semis are the everyday work, but two designated conservation areas change the rules on specific streets.

The Halfway Street Conservation Area, designated in 1985, protects some of the oldest cottages in the borough around Holy Trinity Church, while the Longlands Road Conservation Area of 1992 guards an almost unaltered inter-war estate. Both carry Article 4 Directions, so alterations that are automatic elsewhere in DA15 need a full application within their boundaries.

Kitchen extension interior in a 1930s Sidcup DA15 semi, London Borough of Bexley
Isometric illustration of a Sidcup DA15 home rear extension drawings design
Proposed floor plan
Sidcup DA15

Planning in Sidcup (DA15): what to know before you apply

Within the Halfway Street and Longlands Road conservation areas the Article 4 Directions withdraw permitted development for elevation, roof, window and front-boundary changes, so alterations that are automatic on nearby 1930s streets need a householder application here. Elsewhere in DA15 — the wider Blackfen, Lamorbey and Longlands suburbs — rear and loft extensions on the inter-war semis commonly remain permitted development, subject to the usual size and height limits.

Typical Sidcup housing stock

Sidcup's DA15 stock runs from some of the oldest houses in the borough — the 17th- and 18th-century cottages lining Halfway Street and Burnt Oak Lane — to the almost unaltered inter-war semi-detached estate of Longlands Road, with broad Edwardian and 1930s suburban avenues around Blackfen and Lamorbey in between.

Streets we regularly draw for in Sidcup

Halfway Street · Burnt Oak Lane · Longlands Road · Blackfen Road

What DA15 is actually built of

Measured from 387 classified residential buildings in DA15, not from a description of the area.

Sidcup DA15 housing mix

Residential building form across the DA15 postcode district, from 387 classified buildings.

Attached on more than one side42%
Attached on one side50%
Detached8%
Median building footprint67 m²
Addresses per buildingAbove about 2 means flats and maisonettes dominate1.04
Buildings classified387

Source: Ordnance Survey National Geographic Database (derived statistics). Contains OS data © Crown copyright and database right 2026. Contains Royal Mail data © Royal Mail copyright and database right 2026. Extracted 2026-08-17.

Rear Extension Drawings for Sidcup (DA15) homes: the package and the process

Depth is the number the application turns on, and it has to be measured from the original rear wall of the house rather than from whatever is there now. The drawings carry that dimension, the eaves and ridge heights, the position of any rooflight, and the boundary distances on both sides.

Where the scheme goes beyond the standard allowance and relies on the larger home extension route, the drawings serve a second purpose: they are what the council sends to the neighbours during the consultation. A clear, dimensioned proposed elevation answers the objection about overshadowing before it is made.

Depth is limited by the plot as much as by the rules. A long garden behind a terrace can take the full allowance, while a short one runs out before the rules do — and on a semi or detached house the same depth reads very differently from the boundary.

Do I need planning permission for a rear extension in London?

Many single-storey rear extensions qualify as permitted development, meaning no planning application is needed, provided depth, height and materials stay within set limits. That changes if your property sits in a conservation area or is subject to an Article 4 direction, both of which can remove permitted development rights across a street or borough — in that case a full householder planning application is required regardless of size.

Even where an extension qualifies, most homeowners obtain a Lawful Development Certificate to confirm that status in writing before building — useful for mortgage lenders, buyers and Building Control. We check your property against your borough's constraints before recommending a route.

How deep can a single-storey rear extension go?

Depth is the main constraint on a rear extension, and it depends on your house type and whether you use standard permitted development or the larger home extension scheme.

Permitted development

Standard permitted development allows a single-storey rear extension up to 3 metres deep for terraced and semi-detached houses, or 4 metres for detached houses, generally with eaves height limited to match or stay close to the existing house.

Larger home extension scheme

The prior-approval scheme extends this to 6 metres for terraced and semi-detached houses and 8 metres for detached houses. Your council writes to affected neighbours; if none object within the notification period, approval follows without a full planning application. If an objection is raised, the council assesses the impact on neighbouring light and outlook itself, rather than automatically refusing, so a well-considered design still has a good chance of approval.

Designing the kitchen-diner: rooflights, bi-folds and daylight

Most rear extensions exist to create one open-plan kitchen, dining and living space, so the drawing work focuses on getting light and flow right within the depth you are allowed.

  • Structural opening sized for bi-fold or sliding doors across most of the rear elevation
  • Rooflights or a roof lantern positioned to light the centre of the room, away from the shadow line of the main house
  • Open-plan layout tested against the 45-degree rule, which protects daylight to your neighbours' windows and can limit how close a flank wall or roof comes to the boundary
  • Floor build-up and threshold detail coordinated so the new floor meets the existing one without a step
Rear extension routes at a glance
RouteWhen it appliesTypical fee
Permitted development (Lawful Development Certificate)Depth within 3m (terraced/semi) or 4m (detached), height and materials within PD limitsPD/LDC pack ~£950–£1,450
Larger home extension (prior approval)Depth up to 6m (terraced/semi) or 8m (detached), with neighbour notificationfrom £1,100
Full householder planning permissionExtension exceeds PD/larger-home limits, or the property is in a conservation area with an Article 4 directionFull Planning pack ~£1,600–£2,400
Planning + Building Regulations (structural)Combined planning and construction-ready pack with structural calculations for the opening and roofPlanning + Building Regs pack ~£2,200–£3,850
Sheet from a rear extension drawings package drawn for a Sidcup property in DA15, showing the existing and proposed arrangement at scale
A sheet from the rear extension drawings package we submit to London Borough of Bexley for Sidcup (DA15) properties.

Also in Sidcup DA15

Planning PermissionPlanning DrawingsArchitectural DrawingsBuilding Regulations DrawingsLoft Conversion DrawingsRear Extension Drawings across BexleyRear Extension Drawings across London
FAQ

Rear Extension Drawings in Sidcup DA15 — FAQs

How much does a rear extension cost to design in London?+
Rear extension drawings start from £1,100, with the final fee set by the route your extension takes — permitted development, prior approval or full planning — and whether you need building regulations and structural calculations bundled in. The fee is fixed and agreed upfront.
Do I need an architect for a rear extension?+
No. DrawingsDirect is an MCIAT-chartered architectural technologist practice, producing the same council-accepted drawings as an architect for a fixed fee typically around 30% lower.
How long does it take to get rear extension drawings?+
Drawings are typically ready around 7 days from survey. Once submitted, councils have a statutory 8-week period to determine a standard householder planning application.
What is the 45-degree rule?+
It is a daylight test many London councils apply to check that a rear extension does not block too much light to a neighbour's nearest window, measured as a line drawn at 45 degrees from that window. We check it before submission, not after a refusal.
Will I need a Party Wall Agreement for a rear extension?+
Only if your foundations or new walls sit on or near the boundary with a neighbouring property. A straightforward rear extension set within your own plot often does not trigger the Party Wall etc. Act 1996, unlike a Side Return or Wraparound extension, which usually does.
Do I need planning permission for an extension in Bexley?+
Bexley has no borough-wide Article 4 direction affecting typical householder permitted development, so its semi-detached homes often keep fuller rights than inner-London terraces — larger rear and single-storey extensions can qualify. Conservation areas such as Old Bexley Village and Danson Park, and riverside flood-zone constraints toward Erith, restrict this. We check your address first and can confirm permitted development with a Lawful Development Certificate.
Can I build a bigger extension because Bexley plots are larger?+
Often, yes. The generous interwar plots across Bexleyheath, Sidcup and Welling make substantial rear and double-storey extensions viable where a tight terrace could not. The limit is usually design and amenity policy rather than space. We design to use the plot fully within permitted-development allowances or a well-evidenced full application.
What extra control applies in Old Bexley Village or around Danson Park?+
These conservation areas carry design control over materials, rooflines and front elevations, and the Upton area of Bexleyheath includes the setting of William Morris's Red House. Permitted development is often restricted there, so we design to the area's character and prepare a full, context-led application where a standard permitted-development route doesn't apply.
How long does Bexley Council take to decide?+
Bexley determines most householder applications within the statutory eight-week period once validated; conservation cases can involve additional consultation. A complete, correctly scaled submission is the best way to avoid a validation query — we prepare Bexley drawings to the council's checklist to keep the application on track.
How much do planning drawings cost in Bexley?+
We quote a fixed fee upfront, typically around 30% below an architect's charge for the same council-accepted drawings, with free redraws until Bexley approves. Because plots here allow larger schemes, the fee tracks complexity — a single-storey rear differs from a double-storey — and we confirm it once we understand your plans.
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