Rear extension drawings in London

Prior approval for a longer extension

A deeper single-storey extension can use the prior approval route. The national figure reads: 6 m (attached) / 8 m (detached), single storey, height max 4 m; not on article 2(3) land or an SSSI. The council does not judge the design in general. It looks at the effect on the neighbours, and the neighbours are told and can object.

The clock is short. The rule states: 42. That is a legal default, not a promise about any one council's pace, so we keep the file tidy to avoid questions.

Our prior approval drawings page covers the application in more detail, and the same drawings can be used for a Lawful Development Certificate when the extension is within the ordinary limits.

When a rear extension needs planning permission

Some houses cannot use these rights at all: flats, converted houses, homes where an Article 4 direction removes them, and listed buildings. Others have a design that goes beyond the limits, such as a two-storey rear addition or a flat roof taller than allowed.

In those cases we submit a householder application. The council's fee is £548 for an extension to a single dwelling, paid to the council. Our own fixed fee for the drawings is separate and published, starting at £695.

A conservation area does not stop a rear extension, but it narrows what the officer will accept: materials, roof form and the view from the street. We look at that before drawing.

Building regulations for a rear extension

Even a permitted development extension must meet the Building Regulations. The energy limits for new walls, roofs and floors are: New elements in existing dwellings, limiting U-values W/(m²·K): roof 0.15, wall 0.18, floor 0.18, windows 1.4 (or WER Band B), doors 1.4. Large glazed openings are limited too: Windows, roof windows, rooflights and doors in an extension should not exceed 25% of the extension floor area plus the area of openings removed or covered.

Knocking through the old back wall almost always means a steel beam, so a structural engineer's calculation is part of the package. We coordinate it with our structural calculations and show the padstones and bearings on the sheets.

Our building regulations drawings carry the foundations, drainage and fire details through to the building control submission.

Neighbours, boundaries and party walls

The rear extension is the project most likely to involve the neighbour, because the new wall often sits on or beside the boundary. For deep foundations near their house the Act says: Adjacent excavation notice at least 1 month before work: within 3 m and deeper than the neighbour's foundations, or within 6 m and cutting a 45° line from their foundations.

Serving the notices early protects your programme. A neighbour who dissents starts a surveyor process, which adds time but does not stop the work for good. We prepare the notices and drawings through party wall notices so the paperwork matches the design.

Good relations help more than any form, and a clear drawing of what is proposed is the easiest thing to show a neighbour.

Cost, extras and what you receive

Rear extension drawings start at £695, VAT included, fixed and published before you commit. Larger or more complex shapes are priced from the same list.

Two exemptions are worth knowing about: Residential extensions and annexes can claim exemption (claim before commencement), and for householders: Householder applications are exempt from biodiversity net gain.

You receive existing and proposed plans, elevations and sections, a location plan and a block plan, plus forms and submission if you want them. If the council asks for changes, we redraw at no charge until approval.

Rear extension drawings by council

Boroughs read the same rules differently when it comes to depth, materials and the neighbours' light. Start with the page for your council under architectural drawings by area.

Want to fill the side as well? The next step up is a wraparound extension. Prefer to compare every type? See house extension drawings for the four shapes side by side.