Householder Extensions and Conversions – Page 11

Two-storey rear extensions: the 3m and 7m rules

Two numbers decide whether a two-storey rear extension is permitted development, and neither depends on the house type. Here are the limits, the roof pitch and window conditions, and when to apply instead.

Mansard roof extensions: policy tests and design rules

A mansard rebuilds the roof rather than adding to it, so permitted development is out and the whole argument moves onto design and terrace precedent.

Roof terraces and balconies on house extensions

Every relevant class excludes verandas, balconies and raised platforms above 0.3 metres, so a roof terrace always needs permission. Here is what mitigates overlooking and what to put on the drawings.

Rear dormer design in a conservation area

There is no volume allowance to work within. A dormer in a conservation area is assessed against the section 72 duty, which makes roof geometry the whole argument.

Porches: the 3 square metre rule and where it goes wrong

Three numbers decide whether a porch is permitted development. External measurement and the two-metre highway rule remove the rights from most urban front gardens. Here is how to check yours.

Hip-to-gable loft conversions: when permitted development stops

A hip-to-gable uses more of the Class B volume allowance than most people expect, and the house type that suits the form is often the one with the smaller limit.

Outbuilding size and height limits under Class E

Six numbers and one condition decide whether a garden building is permitted development. Here is how to calculate curtilage coverage, which height limit applies to which roof, and the traps in conservation areas.

The 45-degree rule and how officers apply it to extensions

The 45-degree line is a screening device in council design guides, not national policy. Knowing how it is drawn tells you which part of the extension has to move.

Garden room or separate dwelling: the ancillary test

A garden room stops being permitted development once someone can live in it independently. Here is the section 55 planning unit test, the Class E limits, and how councils tie an annexe to the main house.

Side extensions on terraced and end-terrace houses

A mid-terrace house has no side elevation to build beyond. An end-terrace does, and then three Class A exclusions decide whether anything is permitted development.