Outbuildings building size - climbing wall

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 matt30987 04 Apr 2021

I am looking to build a climbing wall in my garden, and to keep things simple I am trying to avoid building regs.

< 30 square metres internal floor space is the decider for building regs, which I believe is calculated with this:

"Floor area” means the aggregate area of every floor in a building or extension, calculated by reference to the finished internal faces of the walls enclosing the area, or if at any point there is no such wall, by reference to the outermost edge of the floor;

So say I build a 6.1m x 6.1m wood frame building, 100mm insulation. Inside I build plywood climbing wall with an internal area of 5m x 5m. 

What is the internal floor area, 36 sqm or 25 sqm?

The area inside the climbing wall would be the only usable area, you would just have a 1m air gap from internal wall to external wall.

The sizes I have given are for simplicity, its the principle I am asking about, is this a valid loophole?

Thanks in advance.

 jkarran 04 Apr 2021
In reply to matt30987:

No idea where the law stands, it sounds like floor area is floor area irespectivo of wall thickness (so not overall footprint) but why would you want such a gigantic home wall with huge airgaps between it and the shed?


 matt30987 04 Apr 2021
In reply to jkarran:

Because a large 40 deg wall + fall room will need at least 4.65m. I want to have 3 walls side by side, which needs 2.4m x 3 so about 8m wide. Thats 37 sqm. 2 of the walls wont be anywhere near 40 deg so they can come forward and then they would end up taking up about 7 sqm of the floor, bringing the total usable/visible floor space back to 30sqm.

2 walls side by side would fit but I am greedy I want 3 + one on each side (vertical/slab), so 5 total.

With a square of course it would make no sense, but it was easier to explain the point. Does that make sense?

 Fraser 04 Apr 2021
In reply to matt30987:

> The sizes I have given are for simplicity, its the principle I am asking about, is this a valid loophole?

In short, no. 

Your internal area would be calculated on the basis of the shell enclosure, not what you subsequently erect inside that shell. 

You'd be better having the woodie structure being part of the buildings structure. And you'll need more than a 100mm wall structure zone,  nomatter how you intend to construct it. Personally, I'd allow each wall to have a thickness of 250-300mm. A 30sqm building is going to have a fairly decent roof span, requiring quite a meaty supporting structure. Do it right,  do it once. 

 matt30987 04 Apr 2021
In reply to Fraser:

Thanks Fraser. The woodie would be attached to the structure yes, so yes effectively part of the structure. So presuming thats the case does my internal floor area work out like I suggested? 

The 100mm wasnt supposed to be a proper wall thickness, I was just making the maths simple for the question. More than happy to build it right, planning for big strong ridge beam which should make it very strong. 

 Fraser 05 Apr 2021
In reply to matt30987:

Unfortunately, I think that would probably depend on the interpretation of the local Planning Officer, if they were to be made aware of it or receive a complaint. The legislation is clearly there to limit the external size of the structure being built, out of consideration to the neighbours. So if they feel you're stretching things a bit, they might take the hump and report you or ask for it to be investigated. It's not that unusual for owners of garden rooms built under PD being asked to take them down if the building found to be non-compliant.

The other things to bear in mind are the footprint size compared to the size of your garden, (there are limits of what percentage can be built on) also check the height restrictions & proximity to your boundary.

Post edited at 07:25
 TonyM 05 Apr 2021
In reply to matt30987:

Hi Matt

Forgive me if this is teaching you to suck eggs, but there are two main things to think about with outbuildings: planning regulations and building control. 

If you're wanting to build an outbuilding in your curtilage (i.e. your garden/grounds) and don't want to have to apply for formal planning permission from the Council, then you'll want to construct using the deemed permission of the Permitted Development allowances (aka your PD Rights). These dictate all the rules about how much development you can lawfully do and will give you all the measurements about area, heights, proximity to neighbours, etc. This document would become your bible:

If you want to know whether what you plan is lawful before you go to the time and expense of building it then you can to either an informal planning enquiry to the Council, or a formal application for a Lawful Development Certificate (LDC). The latter is more expensive and takes longer, but gives legal protection. The rules are subtly different between England and Wales.

Building control is different and entirely separate within council administration from planning. It's about making sure that buildings are well built and safe. The costs of getting someone to supervise building work to make sure it satisfies building regulations is not that great. Definitely cheaper than formal planning permissions, building plans, etc.

I wouldn't put my effort into avoiding building control, but I would make sure I'm squeaky clean on the PD rights. And obviously, if you want to get on with any neighbours afterwards, talk to them about what you intend to do beforehand! Neighbour disputes can become a total life misery.

Sounds like a fab wall. Enjoy, Tony    

 matt30987 05 Apr 2021
In reply to TonyM:

Hi Tony,

Thanks for the info I appreciate that, however I have already done the research and what I want to build easily fits into permitted development, I didnt mention it as I am confident its not a problem. I have big garden, big house, will have it 2m from boundary, 2.5m eaves 4m total etc etc. 

Neighbours both sides are happy with what I am planning, well they were last year so I will have to mention it again before I start. 


I think I would be unlikely to get away with >30sqm and counting the woodie as "walls". Maybe I just go with having building inspector involved, will force me to build it well at least.

Thanks both

In reply to matt30987:

What counts as permitted development (no planning permission) varies a bit depending upon the opinion of where you're located, so make sure you double check things on website of your local planning authority. Also check if you are counted as a conservation area or other restrictions.

Don't excavate within 2 metres of a shared drain, without checking too, even if you think you own it

Also don't get caught out by party wall regs, even if you don't have what you might consider as a party wall in plain English, if you dig a hole for a footing to build a structure within a certain distance of a fence or property boundary you might be required to notify neighbours etc even if there's nothing remotely resembling a "party wall".

Things aren't a big deal, providing you take time to do your homework on the above. I've had terrible advice from architects and great advice from highly experienced builders, a really good experienced builder is worth paying for.

That's my 2p worth...

 Fraser 05 Apr 2021
In reply to CantClimbTom:

> ....a really good experienced builder is worth paying for.

As is a really good, experienced architect.  

Related question, but does anyone know where the height of a garden structure actually counts from? My garden is sloping towards the back and the previous owner flattened it out with a concrete slab back there. I have a climbing wall on that and I need to build a larger shed to replace the one already there but since there is a concrete slab, I can't tell where exactly the ground level is, there is a half metre step on one end and none on the other. Where the height is measured from would both affect how high I can build the shed and also whether my wall is actually PD (if it isn't I can hinge it to bring it down as needed).

 TonyM 05 Apr 2021
In reply to Alkis:

In England only, it's the highest ground level next to the outbuilding wall. So if you're on a slope, it's the uphill side where the measurement starts (ie. the 2.5m eaves height, 4m for double-pitched ridgeline). That's what it says in the technical guidance on PD rights in the link I gave previously. 

But ... this is an area of some contention and challenge. The legislation doesn't actuals say "natural ground level", but that is the way that the Planning Inspectorate have tended to interpret the rules. So if you pile up the ground to artificially elevate the highest point of the ground level, then you can fall foul of enforcement activity.

Hope helps. If in any doubt get an LDC before commencing development.


 jkarran 06 Apr 2021
In reply to matt30987:

> 2 walls side by side would fit but I am greedy I want 3 + one on each side (vertical/slab), so 5 total.

> With a square of course it would make no sense, but it was easier to explain the point. Does that make sense?

Not to me, it sounds rather wasteful. If you were really looking for an excuse to build a barn, sure, but if you actually want a decent home climbing wall I'd think again about how to better use the space. Best home wall I ever used fit into a shed of ~5sqm footprint. The creativity that made it great was driven by the tiny space but the ideas are still good when space isn't at such a premium. I say that as someone who built a big, lazy, wall in lots of space because I had it. I wouldn't do it again even in the same position.


In reply to Alkis:

It's kinda complicated, it depends where the wall is built from. This video explains it well:

Post edited at 11:06

Thanks Tony, with all that in mind, I've sent an inquiry to my local planning office to see what they have to say, sounds foolish for me to do anything without clearing this up first. 

In reply to Paul Phillips - UKC and UKH:

Very interesting. I'm still not entirely sure where I stand, because I'd be building on an existing concrete slab, so let's see what the planning office has to say about it.

 andyt33 07 Apr 2021
In reply to matt30987:

You’re best off submitting a certificate of lawful development prior to building anything. I do planning and architectural services, in addition to climbing.  

Happy to assist for a small fee. You have to be careful as it’s measured from the bottom of the slab usually. A previous client got caught out with this and the council made them submit a retrospective planning application and are now very unpopular with neighbours (even tho it was approved). Look at the interactive house on planning portal. I doubt the council will come back with anything useful, they certainly wouldn’t give you verbal permission to build. You have to be abit careful on the use of the building too as councils get upset about large ancillary buildings in gardens sometimes. 

 matt30987 08 Apr 2021
In reply to andyt33:

Hi Andy,

I have decided to go with something under 30m to avoid building regs, as JK alluded to I think that is plenty big enough.

To make the most of the height I need a cathedral style roof or vaulted ceiling. I'm looking at an internal size of 4.2m X 7.2m. My concern for a ridge beam design a 7.2m span is quite significant, and even though I have looked on to get sizing, I am not convinced I can design and build a structure that is strong enough without a little help.

Could we perhaps message privately to discuss if you can help in that regard?

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