Roof height of outbuilding difficult to assess due to uneven ground

[Shlomi]

Hi guys, hope someones got some good grasp of the building regs and permitted development and how they may apply to my scenario. Just had a company to lay a 7x3 meter concrete slab at the rear of my garden bordering two neighbours.I'm planning to build my woodwork workshop on top of the slab and need to figure out how to maximise the size I can build on top of this pad, and how to get the maximum internal head height while sticking to the regulations. The slab is 20cm thick, 10cm below the garden lowest point and 10cm above the lowest point. However, it was obvious from the start that our garden level is very uneven, and that in some parts the slab is actually below the surrounding soil level especially around the fences where the neighbours garden begins at least 20cm above the pad level. For that reason I'm thinking to build a retaining wall to keep the soil at bay. I'm attaching some photos to help assess my first question which is, what would be a viable point to measure the 2.5m external roof height as per permitted development within 1m boundary of the fence? Do I take the lowest part of the garden as a reference, the highest point or possibly measure it from the slab itself? Is it a matter of being sensible or is there a hard and fast rule to go about this? In an ideal world I would like to be left with 2.4m internal height, after deducting the wooden base and cold roof insulation which will probably amount to 30-40cm. But if my ground level is the lowest point and my slab is 10cm above that, then I'll be left with 2m head height. If I measure from the slab then I might get 2.1m and if go from the highest points I might be able to gain myself another 20-30cm. That of course will increase the chances of neighbour complaints as the outbuilding will go well above the fence and that even might lead to an inspection ,a position which I really don't want to find myself in.

Any thoughts, advice, or similar experiences to share will be most appreciated.

Shlumaan

[torre]

 

Government permitted development advice looks like it'll work to your advantage...

 

Where ground level is not uniform (for
example if the ground is sloping), then the ground level is the highest part of the surface of
the ground next to the building.)

 

You could apply for a certificate of lawful development to remove any doubt

 

[gaz_moose]

in england its 2.5 from the highest point.

a dual pitched roof will gain you the most internal headroom.

what are you building the walls out of?

[DevilDamo]

You’re limited to an overall height above ground level of 2.5m. Anything more, then you require Planning. If you’re wanting or needing an internal height of 2.4m, you’re going to need Planning.

 

The height doesn’t have anything to do with Building Regulations. To keep it BR exempt, it will need to be constructed substantially of non-combustible materials. Otherwise, you will require BR’s.

[garrymartin]

56 minutes ago, DevilDamo said:

You’re limited to an overall height above ground level of 2.5m.

Because you're within 2 metres of the property boundary...

 

On 04/08/2024 at 08:21, gaz_moose said:

a dual pitched roof will gain you the most internal headroom.

You can't have a dual-pitched roof because you are within 2 metres of the property boundary and hence maximum height is 2.5m

 

58 minutes ago, DevilDamo said:

To keep it BR exempt, it will need to be constructed substantially of non-combustible materials.

If the INTERNAL floor area is less than 15m2, then it is BR exempt. If between 15m2 and 30m2 then it must be constructed of substantially non-combustible materials because you will be less than 1m from at least the rear boundary.

[DevilDamo]

@garrymartin This is not my post so is not my project. The photo clearly shows it is within 2m of the boundary. The post mentions an (external) floor area/slab of 21sq.m so the internal area will be more than 15sq.m and it’s within 1m of the boundary. So you don’t really “need” to re-quote me.

Edited August 18 by DevilDamo

[garrymartin]

@DevilDamo The comments were all meant for the original poster as an attempt to clarify the reasoning for the various things that had been mentioned in the various posts. It wasn't my intent to offend anyone. Apologies if that inadvertently happened.