Householder Extensions and Conversions

Light wells, front gardens and basement conversions

The excavation is often invisible in planning terms while the light well changes the front elevation. Here is how the two are assessed, and where party wall and drainage duties bite.

Outbuilding eaves heights and the boundary rule

The 2.5 metre boundary cap and the 2.5 metre eaves limit are different rules that apply together. Both are measured from the highest adjacent ground, which is where garden rooms go wrong.

Raising the ridge for loft head height

Class B does not permit an enlargement above the highest part of the existing roof, so any ridge lift is a full application. Check the head height numbers before you commit to one.

Annexes and the ancillary use test

Planning does not care who lives in an annexe. It asks whether the accommodation is ancillary to the house or a separate planning unit, and the answer changes everything about the application.

Roof terraces on a rear extension and overlooking

Balconies, verandas and raised platforms are excluded from Class A, so any roof terrace on a rear extension is a full application. Here is how overlooking is assessed and what mitigation works.

L shaped dormers on a terrace: what Class B allows

An L shaped dormer is one enlargement across two roof planes. Whether the 20 centimetre set back applies to the lower limb depends on whether the back addition is original.

Rear dormer proportions and the 20cm eaves set back

The 20 centimetre set back is measured along the roof slope from the original eaves, and it changes the dormer's proportions and the headroom at the back wall.

Hip to gable loft conversions and the 50 cubic metre limit

Class B allows 40 cubic metres on a terrace house and 50 otherwise, measured against the original roof. Filling one hip end takes a large share of it.

Wrap-around extensions and the two storey element

A side return joined to a rear projection is tested against the side and rear limits of Class A at the same time, and usually fails both. What that means for the application.

Conservation rooflights and how they are specified

Class C allows a rooflight protruding no more than 150 millimetres from the roof plane, including in a conservation area, but the detailing and position decide whether an officer accepts it.

Rear extension depth: the 3 and 4 metre lines

Class A allows a single-storey rear extension of 3 metres on an attached house and 4 metres on a detached one, with deeper extensions only through the prior approval procedure.

External wall insulation on a terraced elevation

On designated land, render and cladding fall outside Class A entirely. Elsewhere the similar appearance condition decides it, and on a terrace the party wall junction, eaves and reveals decide the design.

Why loft conversions in a flat need permission

Article 2(1) of the GPDO excludes flats from the definition of a dwellinghouse, so Part 1 gives a top-floor flat no rights, not even a rooflight. Internal work is a different question, and the lease is usually the harder one.

Converting a house into two flats: amenity and storage

Section 55(3)(a) makes subdivision a material change of use, so there is no permitted development route. What decides these applications is room sizes, outdoor amenity space, bin store design and cycle parking.

Dormer proportions and what design guides ask for

Once a dormer needs permission the test becomes design rather than arithmetic. The set-ins, proportions and materials design guides ask for, and how to argue a departure.

What obscure glazing means in a planning condition

Obscure glazing conditions require the obscuration to be a property of the glass and the window to be fixed below 1.7 metres. What the levels mean and what happens if the glass is swapped.

Rear extension depth on a corner plot

Class A excludes an extension projecting beyond a side elevation that fronts a highway, which is why wrap-around extensions on corner plots need an application while a straight rear extension often does not.

Garden room height and the two metre boundary rule

Class E of the GPDO caps an outbuilding at 2.5 metres where any part sits within 2 metres of a boundary, and at 3 or 4 metres beyond it. How the limits are measured, and how to design within them.

Designing a basement under a terraced house

Depth, extent beneath the garden, soil cover and light well design decide most householder basement applications. The structural and hydrogeological evidence does the rest.

Loft conversion stairs and the planning drawings

The staircase decides how much of a loft is usable and where the dormer has to go. The section through the stair is the drawing that settles whether a conversion works.

Flat roof against pitched roof on a rear extension

The 4 m overall and 3 m eaves limits in Class A decide most rear extension roof forms. Once you are applying for permission, the design guide takes over and often prefers a pitch.

Setting back a two storey side extension

A two storey side extension always needs planning permission, and setting the front wall back from the original frontage is usually the change that turns a refusal into an approval.

Lighting a deep single storey rear extension

Daylight falls away fast from a vertical window, so a deep rear extension needs light from above or from the side. The decisions have to come before the steelwork.