Converting Your Loft – Design Implications, the Exterior

In my 1st blog, we looked at the outline issues in converting your loft. This 2nd blog looks in more detail at the limits on what you can build and the resultant implications on the overall volume you could create.

Fixed physical boundaries

Your loft has fixed physical boundaries (the roof, the ridge and the ceiling below). These will ultimately be the limiting factor in the additional space you could create.
The extra space you can create by converting your loft will be determined by the size of the overall structure you are allowed to build and how much you can and want to push these fixed physical boundaries.
The size of the structure you are allowed to build will be primarily governed by whether you need planning permission or if can do the works under Permitted Development (PD) rights.

Unless you have other limitations (finance?) you may wish to go for the route that has the least ‘regulatory hoops to jump through’ and the one that should allow you to maximise the space you can create.

Planning Approval or Permitted Development?

If you need planning approval for your loft conversion the restrictions imposed upon you by the planning authority will limit the additional space you can create in converting your loft.
A loft conversion carried out under PD should enable you to exploit the full potential of your loft space. However, there are limitations when converting your loft under PD and you cannot do just as you want.

Planning Approval

Your Local Authority will have their own policies and design guidelines for converting lofts. Planning policies vary across the country but planning authorities do not usually support planning applications considered to have a visual and a negative impact on the roofs of properties. These will often include; alterations to the front roof slope, un-balancing pairs of houses by adding a hip-to-gable at the side and full width or box dormers to the rear roof slope.
You may be able to get planning approval for one or more small dormers, which will create more standing space in your loft. If you are lucky you may be able to get you loft stairs to fit into a dormer.

Permitted Development rights

Your Permitted Development (PD) rights for loft conversions are set out in a nationally produced document [link to doc].

Summary of the key PD rights for loft conversions

Any additional roof volume (including previous loft conversions) must not exceed: 40 cubic metres for a terraced house, or 50 cubic metres for a detached or a semi-detached house
No conversion works (except roof lights in the same plane as the roof slope) to extend beyond the plane of the existing roof slope that faces a road
Materials to be similar in appearance to the existing house
No part of the conversion to be higher than the highest part of the existing roof No verandas, balconies or raised platforms
Side-facing windows to be obscure glazed and non-opening below 1.7 metres
Conversions, apart from hip-to-gable, to be set back 200mm from the original eaves, measured along the roof plane

What can you do under PD?

Provide you keep within your PD rights, particularly the volume limitations, you can maximise the volume of your loft conversion by;
A Box Dormer. You can build a full-width box dormer to the rear roof slope of your home
A Hip-to-Gable. You can convert the hipped roof at the side of your home to gable
Convert the Outrigger loft. If you have a loft over your rear-facing outrigger this could be part of your conversion works

Interpretation of your PD rights

Interpretation of your PD rights can be quite complicated. If you are in any doubt or if you require legal confirmation you should submit an application for a Certificate of Lawfulness. A Certificate of Lawfulness is legal confirmation you do not need planning permission for the proposed works.

For details of my other loft blogs please check out my website:

Please note this is a guide and is not a definitive source of legal information.

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