20cm setback rule - Public forum - Planning Advisory Service (PAS)

Hi David,

Where you have an existing secondary roof that's significantly lower than the main roof (or the main roofs), then in my opinion it's debatable whether an extension to such a lower roof should be assessed against Class A or Class B.

It's worth noting that if these types of works are assessed against Class B, then this would result in a number of very significant loopholes.  For example, it's clear that two-storey side extensions (and first floor side extensions) are supposed to be prevented by the legislation.  And yet, for a typical two-storey property with an existing single storey side extension, if the view is taken that an extension to such a lower roof should be assessed against Class B (i.e. rather than Class A), then this would potentially allow a first floor side extension (e.g. in the form of a dormer set-back from the eaves, etc).  Similarly, for a typical two-storey property with an existing single storey rear extension, this would potentially allow a first floor rear extension up to the boundary with the adjoining property.

Unfortunately, there haven't been many appeal decisions relating to this type of issue, and the ones there have been have mostly contradicted one-another.  For example, I've seen 2 appeal decisions that concluded that an extension to a lower roof should be assessed against Class A, 1 appeal decision that concluded Class B, and 1 appeal decision that concluded Class A and Class B ... which doesn't help very much!

Thanks,
Steve

Thanks Steve.

I take your point that Class B is designed to cover roof extensions and not to allow for accommodation above single storey offshoots but unfortunately I think this is a loophole.  If a garage to the side of a property has a pitched roof on it then I dont see any reason why a dormer couldnt be added under Class B.  I think its just another area where the government hasnt thought through the legislation properly.

The scenario I have is slightly different.  A single storey offshoot is merely seeking to have a replacement pitched roof to replace the flat one but the principle is the same as say the addition of a pitched roof over an existing two storey flat roofed side extension to make it match with the house.  Class A excludes roof alterations from being made so I would have thought the next step would be to look at Class B as the property is still being enlarged but this time by a roof.

My scenario involves no raising of the eaves level, meets the volume requirements, meets the side facing windows conditions and meets the materials conditions.  The only sticking point seems to be the 20cm setback condition which is only to be applied where practicable.  Can an argument therefore be made that because there is no existing roof slope to measure up, setting back is not practicable?  Or does this simply mean that no permitted development exists in such scenarios?

Hi David,

If you do assess such works against Class B, then as you indicate it's difficult to know whether the new pitched roof would only be permitted development if it's set-back from the edge of the existing flat roof by 20cm, or whether it's the case that such a set-back would not be "practicable".

Although the DCLG "Technical Guidance" document advises that the 20cm set-back should be "measured along the roof slope", in my opinion this is simply providing advice for the most common scenario of a proposed dormer on an existing pitched roof (for which the direction of the roof slope is the shortest distance), and doesn't necessarily mean that it's not possible to measure the 20cm set-back for an existing flat roof.  Indeed, the legislation itself uses the phrase "not less than 20 centimetres from the eaves of the original roof", which doesn't necessarily mean that this measurement will always have to be in the direction of a roof slope.

In terms of appeal decisions, Inspectors have generally taken quite a restrictive interpretation of condition B.2(b), and have tended to reject arguments that the 20cm set-back would result in additional cost, or additional delay, or reduced internal floor space, etc.  The only examples of appeal decisions (that I'm aware of) where Inspectors have concluded that the 20cm set-back is not practicable have tended to be where a property has an original rear projection at a similar level to the main rear roof (i.e. an "outrigger") for which it's proposed to erect an L-shaped rear dormer that would extend from the main rear roof onto the side roof of the original rear projection (and which would therefore extend across part of the original rear eaves without the 20cm set-back).

In terms of your particular situation, the only appeal decision I've seen that involved the proposed replacement of a flat roof with a pitched roof was APP/P2365/X/12/2179324, which was 1 of the 4 appeal decisions that I mentioned in my post above.  Indeed, it was the appeal decision that concluded that such works should be assessed against Class A and Class B.  Unfortunately, this appeal decision doesn't help your assessment, because the Inspector dismissed it on the basis that the works would exceed the volume limit under limitation B.1(c), and didn't proceed to assess whether or not the works would have complied with condition B.2(b).

Thanks,

Steve