Outbuilding help

12 Dec 2009
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United Kingdom
I’m in the process of starting an 7m x 3m outbuilding footings,engineering brick,slab and block up to max 2.5m height flat Firestone membrane roof,Less than 1m to boundary.been told by local planning anything 2.5m height and less then 30sqm is ok but my plan was to go less than 1m to boundary...do my materials class as non combustible and without planning?

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2 things:

2.5m height is from ground level to top of building.

Less than 1 metre and between 15-30 metres square is a building regs stipulation.

If non combustable materialmthen exempt.

I’m taking the 2.5m height from existing ground level of 2 brick below damp...my only concern is the less than 1m boundary

But assuming slab,block are non conbustible my only concern is does the firestone membrane roof covering class as non combustible instead of felt roof ?
Build a parapet wall if you can't convince building control on the suitability of the roof covering.
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The grey area is of course your roof finish.
The nearest you will get from the current regs is that a bitumen-felt roof finished with 12.5mm limestone chippings is accepted as 'substantially non-combustible'.
Regs don't refer to the modern materials such as rubber or GRP. However, the nearest material they quote and which can be acceptable without limestone chippings is
macadam (!?).
On this basis, personally I'd go ahead with rubber - no-one will bother and within a year, you'll almost certainly be in the clear. There must be thousands of ramshackle timber sheds and garages built next to a boundary up and down the country.
IIRC, there is a diagram in the Technical Guidance which confirms that the eaves on a flat roof with a parapet is the horizontal line where the top surface of the roof cuts through the parapet, otherwise we could have parapets 150ft high.
There's an inspectorate decision on this IIRC - eaves are eaves and parapets are not eaves so not covered by the height restrictions.

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