Digging down foundations.

[DTB1985]

So been inspired to start planning a workshop build whoever as with many of us would like to do it within permitted development. I Can't get the build 2m from all boundaries (standard suburban garden) which leaves me with the 2.5 max height limit.

Does anyone know if your allowed to dig and pour the concrete base between 50cm and 1m down and measuring the 2.5m from the existing garden height? This would give you an overall height of 3.5 (if dug down by 1m) but measured from "Ground Level" would not exceed the 2.5m restriction.

I apricate the difficult of this in effort, time and money but just looking to see if this would even pass permitted development first.

I'm interested as being 6'5 (2m) I'd imagine the small amount the slab might be above ground level and the depth of the internal roof beams I'd have very little room between my head and the ceiling hence would really appreciate the extra internal height.

Any advice is greatly appreciated.

 

[Lons]

You would likely be introducing damp or water issues unless you carefully tank below ground but in answer to the question, in all my encounters with planning in regards to buildings ground level is the important factor so yes I can't see why not.

There have been instances where when building on an area raised from the rest of a garden, when sloping for example, we have levelled the area to drop existing ground level and gain height.

Remember if you built a normal structure and then added pavers on top, should neighbours object then the planners are quite likely to measure from top of paver as ground level. Some of them don't seem to have much commonsense.

 

[MikeG.]

This is allowed, but it isn't absolutely straight forward. I'll come back to this later.

 

[Sawdust=manglitter]

I couldn’t tell you about the planning side of things, but as already mentioned you’d have to make sure that you tank it correctly below ground level to avoid significant water/damp issues. Also make sure that a proper structural engineer designs the retaining wall for you (not necessarily as straight forward as just building a standard cavity wall below ground).

Depending on how close to the boundary you’ll be building and whether there is a building next door you may need party wall agreements in place and ensure that you don’t undercut next door (you won’t be able to dig down deeper than the same distance away from the boundary without undercutting the boundary - so if boundary is 1m away then max depth dug will be 1m).

Presumably building control would also need involvement at certain points of the build, who will also need the engineers calculations to satisfy him.

Not trying to put you off it or anything, it’s more than doable, but just making sure you know what you might be getting yourself into both physically and financially.

 

[sunnybob]

You absolutely must get advice from your local council. Different areas have different rules, and it depends on the subsoil.
I have a friend who lives on the somerset levels (which is mainly peat bog and mud). he had to put HUGE foundations in to stop sinkage.
If youre on rock thats different again. only local knowledge will give the correct advice.

 

[MikeG.]

Returning from dinner.......

..........for a start, don't plan on going a metre deep. That's just too deep to deal with without structural engineering and some serious drainage solutions. I would suggest that 450mm is about a sensible limit, and even that depends on having favourable soil conditions. As an example, a single garage 6m x 3m excavated a metre deep will produce about 35 or 40 cubic metres of spoil. That's 6 or 7 big skips, or about £700 or £800 just to get rid of the soil, let alone dig it up in the first place.

I guess my over-arching comment is this: why are you so afraid of applying for Planning Permission for the workshop that you actually want? It won't cost as much as the muck away I've just quoted to get some drawings done and an application submitted, and frankly a decently designed proportionate outbuilding behind a house is almost never controversial or turned down, in my experience. I would certainly explore that before getting into the world of massive excavations, external tanking, engineered retaining walls, sump pumps, land drains possibly with a lift pump in a chamber, and so on. I've built a semi-underground house: this sort of stuff really isn't for the faint hearted.

 

[DTB1985]

Wow, thanks for all the advice and in such a short amount of time .

Lons: Yeah damp would be my primary concern and the main reason I probably won't do this, just exploring every avenue. Thanks for the tip with the pavers, will keep that in mind.

Sawdust=manglitter: Thanks and I will take your words of wisdom to heart. The structure is at the end of our garden with no buildings to either side and behind us is a cul de sac so hopefully no party wall issues.

Sunnybob: I will contact them in due time and in the meantime I've been searching through everything I can find on there website. Regarding our soil I'm no expert but I think were probably in the middle. Not the worst soil but not the best. Saying that we live near a park with 2 lakes and our neighbour across the way informed me that somewhere near us (maybe even in our garden) is one of the sources for this lake. It would explain why our conifer trees are 3 time the size of everyone else lol.

MikeG: I think you might be right here and I'll look at putting in for planning. Guess I'm just a bit scared as feels like opening a massive can of worms but its looking like digging down might be a huge barrel of worms in itself lol. There's a lot I don't know about planning however I suppose that's what the planning department is there for. By the way if it's the the Mike G I think it is I must admit your workshop got me inspired and thank you for the brilliant write up and all the pictures. It's been great to use as learning material and it looks great to boot.

With all the above said I think I'll now look at designing something that will likely require planning. I very much like the look/appeance of Mike G's workshop (wooden frame covered with feather board) and will likely try to come up with something similar. If anyone has any advice generally regarding going for planning I'd appreciate that as it's all very new to me and if I do go for planning would I need to have Building Control involved? Again not a set of people I've dealt with before and I imagine people who like there paperwork.

Again thanks for all your help, its been greatly appreciated.

 

[Lons]

I agree, the planning route is the way to go if you really want to do it properly and if you sell your house it can be an asset to the property.

If the building is classed as non habital ( e.g. described as a store room ) then in my experience building control won't be interested however, put in heating and electrics and they most definitely will be and will require electrics to be signed off.
Might be worth the inclusion on the plans for the provision of a woodburner if maybe on your future wishlist.

You don't normally need a structural engineer for a wooden building which is not classed as a permanent structure and it's not difficult to draw up your own plans for submission though should be to recognised scale and include location plan which you have to buy from the local authority as it's subject to copyright. All the planners are really interested in is location, size and materials to be used. They will want to know what's nearby for possible fire risk.

 

[MikeG.]

.......With all the above said I think I'll now look at designing something that will likely require planning. I very much like the look/appeance of Mike G's workshop (wooden frame covered with feather board) and will likely try to come up with something similar. If anyone has any advice generally regarding going for planning I'd appreciate that as it's all very new to me and if I do go for planning would I need to have Building Control involved? Again not a set of people I've dealt with before and I imagine people who like there paperwork.....

Yes, I am that MikeG.

For planning you'll need a site and location plan, plus a floor plan and all 4 elevations of your workshop drawn to scale. If you keep the building under 30 square metres internal floor area and more than a metre from the boundary then you won't need Building Regs approval. There's a reason my workshop is 29.99 sq m internally. If you want help with the drawings and can wait a few weeks drop me a PM.

 

[Lons]

Is that right Mike Or have I got it wrong?

Under 30 square metres applies to planning approval but as far as I know the size has no bearing on whether the structure requires building control approval and it will still be subject to the rules in part L especially for electrics and wood burner if fitted.
Electrics would have to be fitted by a registered electrician or if by a "competent person" would have to be approved by BC.

It has also been known for BC to get a bit stroppy where drainage hasn't been properly accommodated especially where it causes a problem for neighbours. That's co-incidently something one of my neighbours is having to deal with after he put up a 4x3 gazebo and paving and pushed the rainwater on to his neighbour who got the local authorities involved. They basically told him to redirect the drainage or demolish the gazebo!


Bob

 

[MikeG.]

Is that right Mike Or have I got it wrong?

Under 30 square metres applies to planning approval but as far as I know the size has no bearing on whether the structure requires building control approval and it will still be subject to the rules in part L especially for electrics and wood burner if fitted.......

No, you've definitely got it wrong.

A building under 30 sq m isn't controllable, with the exception of compliance with the electrickery regs, and the electrician can/ will do this for you. Part L will not apply unless it is a habitable room. Build a workshop under that size and you've no need to get the building inspector involved.

There are a variety of size criteria for Planning Permission/ Permitted Development rights, but 30 sq m isn't one of them. The principle one is that you can't cover more than 50% of the original amenity space (garden) with outbuildings without permission.

 

[Lons]

Is that right Mike Or have I got it wrong?

Under 30 square metres applies to planning approval but as far as I know the size has no bearing on whether the structure requires building control approval and it will still be subject to the rules in part L especially for electrics and wood burner if fitted.......

No, you've definitely got it wrong.

A building under 30 sq m isn't controllable, with the exception of compliance with the electrickery regs, and the electrician can/ will do this for you. Part L will not apply unless it is a habitable room. Build a workshop under that size and you've no need to get the building inspector involved.

There are a variety of size criteria for Planning Permission/ Permitted Development rights, but 30 sq m isn't one of them. The principle one is that you can't cover more than 50% of the original amenity space (garden) with outbuildings without permission.

Yep I know about the general regs Mike though I retired a couple of years ago so a bit out of date but the 50% rule hasn't changed.

I don't think anything I said is wrong except I intended to say part P not L for electrics. I didn't say it is subject to building regs just that as far as those regs are concerned size of structure isn't applicable.

A building under 30 sq m isn't controllable

As a general observation that statement could be misleading as it suggests even habitable rooms are exempt although in the case of the OP workshop is valid as it would be in category E of the planning rules.
Any size construction can be subject to building regs depending on location and category in which case part L could also apply.

I did clearly outline the electricity issue and my comment on woodburners is also valid as is the provision of drainage although that wouldn't come to light unless causing a nuisance, as in the case of my neighbour.

There can be other issues, on a small house that's already had maybe a porch, conservatory and garage you could easily exceed the general 50% rule.
A friend who lives in the Northumberland National Park had to apply for retrospective permission when he put up a large shed for his lawnmower at the bottom of his garden, he was promptly advised that as it was more than 10 sq m and further than 20 mtrs from his house he needed planning permission.

I'm pleased to be out of the building business as some of the planners encountered were little Hitlers, especially when it came to listed buildings. BCOs were great though as and most of them just wanted to help find a way around problems. It didn't hurt that I used to teach part time at college and took 2 of them through their plastics material assignments. :lol:
cheers
Bob

 

[MikeG.]

I definitely typed "outbuilding", not "building". Some malicious leprechaun obviously scrubbed it to give himself a giggle. #-o :lol:

But yes, the decision on whether a building is controllable depends on its use, as you say. An outbuilding, however, is not generally controllable if smaller than 30 sq m and at least a metre from the boundary. That area was chosen, incidentally, because it allows an orthodox double garage to be built without inspection.

The thing you got wrong was "30sq m applies to planning". It doesn't. It applies to Building Control.

 

[tony_s]

"So been inspired to start planning a workshop build whoever as with many of us would like to do it within permitted development."
Sorry, what does this mean?

 

[MikeG.]

I think if you read the "whoever" as "however" you'll get the intended meaning.

 

[DTB1985]

Wow, thanks for the typo cath and yup that’s exactly it. Literally been over and over that trying to find the error. Must have gone word blind.

 

[Lons]

Some malicious leprechaun obviously scrubbed it to give himself a giggle. #-o :lol:

My problem is usually fat fingers and sometimes a "fat" head after too much vino. #-o

 

[DTB1985]

Been doing some more digging/design trying to figure out what I can fit.

Looking at our land registry plan it appears our garden is longer than I thought. It seems the trees behind our back fence our actually within our boundary which means I could build the structure right up to the rear fence and still maintain the 1m boundary for building regs.

Here's a (really low rez, sorry google earth) picture of what I mean. Red Line = boundary, blue line = existing fence:

Unfortunately the trees at the rear and one to the front make me think I'll have to do a raft foundation? Does this seem suitable/the best option to people when dealing with trees or is a slab still ok? I suppose it depends on the type of soil/tree to a large extent.

Also done a quick sketch of what could fit without needing building regs:

I am giving seriously consideration making it wider and going for building regs as the storage/shed area could really do with being bigger. If anyone has any experience with building regs I'd appreciate knowing how it was for you and if it'd just be easier to give up on the space and make my life easier?

I'll try and take some pictures of where I intend to build and post so you can see.

Finally I appreciate the offer of help Mike and might call you up on that but will do most of the groundwork first so as not to waste your time. Again many thanks for the offer.

Cheers.

 

[DTB1985]

Been doing more reading (dangerous I know) and I think I was wrong re raft foundations.

It might end up as trench foundations and quite deep ones with the tree's however any advice is appreciated if there is a more economical way that people know of.

Using the NHBC 4.2 Standards to try and get myself informed but some heavy reading there. Going to measure how many trees, how far and what type. Also looks like I'll need to determine our soil type but not sure how to do that yet.

At the moment I'm thinking I'll avoid building control unless someone here can advice me differently as it seems it will add another level of complexity.

 

[MikeG.]

Please don't start designing footing based on what you've read on the internet. I'm happy to help on this, but I'm not going to do it live on the internet. If you want me to sort this out for you, you know how to get hold of me.