Garden office/shed

27 Apr 2011
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United Kingdom

I am planning to build a large shed/office in my back garden at some point soon.
I plan to use this thread to come back to whenever questions arise but I have 2 main ones before I can consider the design and size etc.

I do want this building to basically last forever and to start with I will mainly be using it to store my work stuff. Doors, windows, tools, scaffolding, Ride-on mower, Cement mixer etc.
At a later date I may want to convert it to a man cave something else.

1. Timber frame or block and render?
I do worry about rot in modern timber. As I will likely be sinking the floor slab and footings as low as possible to keep the Eaves under 2.5m for permitted development.

2. Building control sign off, Should I bother?
I was planning to go under 30m2 but have recently seen my friends 70m2 garden office and it was awesome so I might go around 50m2, He did pay building control around £400.
This is probably my forever-house and I definitely wont be selling in the next 10 years or so.
I will be over engineering things and getting advice from my other trade friends along the way.

I cant see the point in wasting £400 for a piece of paper.
Having said that I do have a neighbor that will probably complain to the planning department (he complains to them when I park my van on my drive even though its allowed). Planning wont be a problem as my garden is huge and I will be staying 2m from the boundary's but would they inform building control?
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if you ever plan to be in it during the winter, I'd go timber frame/SIPS. I used 100mm celotex in walls and ceiling and 50mm + 100mm poly in the slab. I can heat mine 5m X 4m with a 1kw fan heater on for a few mins every hour. I wrapped and glad mine and used marine ply to reduce rot.
Right I have been thinking this over for quite a while now and I'm going to have to rule out a conventional base.
The end of my garden is about 70m away from my drive with a 1m access past the garage. Its just too much soil and concrete to be moving up and down the garden.

Final external size is going to be approx 9m by 4m. Walls will be timber frame and I plan to do a gable roof with a 4m high apex.

So I need base ideas.
I'm thinking concrete pads approx every 2m (600x 600 x600 deep) and then either a steel frame with timber floor joists in between or possibly block and beam with 50mm underneath for airflow.
I'm thinking steel and timber would be my best bet as I could insulate below finished floor where as block and beam would have to be above.

I need to keep the finished floor as low as possible for the 2.5m eaves and ideally I would like 2.1m high bi-folding doors.

Has anyone done anything or seen anything similar? or is this just a bad idea?
The plan is to leave a 2m path down the sides and around the back (2m from boundary) and come right upto the plumb tree, Hopefully without killing it.


Looks great, I'll be watching with interest! I guess your plot is 8m wide, ours is only just over 7, so keeping within the 2m would be harder. With your clearances, a 4m apex should be ample!
Your base sounds ample, unless are you on clay with any roots nearby? We are so I was thinking similar but deeper.
Bear in mind PD is just for uncontroversial development. You can apply for a less compromised development if it would be better for you and not be worse for the neighbours. Actually the neighbours opinion doesn't strictly matter as planning law is specific about what is a consideration. Just a thought.
And good luck!
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9M x 4M will give you a floor area over 15m2, so your entire build will need building control approval.
4M is the absolute maximum height, so I'd plan to come in under that just in case you are out by a CM or 2. How close to your boundary will you be?
If you don't mind a step, I'd be tempted to set the floor about 150mm off the deck, so that you could insulate under the floor.

You'd need about 8M2 of concrete for an insulated slab. Personally I'd bite the bullet if you are set on the dimensions.

Given the size, I think I'd go conventional block build.
I think I am ok with 30m2 internal size?
We will be 2m from the boundary in each direction. Width is about 12.6m fence to fence and the right hand fence is mine so technically I will be about 8.6m wide.
Building Regulations: General information

If you want to put up small detached buildings such as a garden shed or summerhouse in your garden, building regulations will not normally apply if the floor area of the building is less than 15 square metres and contains NO sleeping accommodation.

If the floor area of the building is between 15 square metres and 30 square metres, you will not normally be required to apply for building regulations approval providing that the building contains NO sleeping accommodation and is either at least one metre from any boundary or it is constructed of substantially non-combustible materials

I am a bit out of the way and everything down here costs more, Skips, Concrete, materials etc. Plus I am planning to do this on my quite days through the winter so I was hoping to not destroy the garden too much. Plus with the 1m access everything will have to be wheel barrowed.

As mentioned yes I would plan to stay a touch under 4m for the ridge.

I do know a couple of people in the steel trade so I was thinking I could get a few length of steel layed out (possibly small RSJ's so I can fit timber joists between them) and then either bracket them all together or get someone to weld them together.

So something a bit like this but in steel
If I absolutely have to I could just go all 3m high with a flat roof but a 4m roof would give me added privacy from the houses behind assuming I can keep finished floor level as low as possible.
Constructed of substantially non-combustible material means you'll be faffing about with fire proof paint etc.. if you go for a timber construction. Also you are still over 30M2 with your revised dimensions - though I'm not sure what the definition of floor area is. If its internal floor area you might be OK allowing for the thickness of the walls. I think I'd want to insulate between the frame, perhaps some sort of under boarding or a membrane and battens.
constructed of substantially non-combustible materials
I think the substantially non-combustible materials is if your within 1m of the boundary? I'm going to be 2m away.
I may also clad the outside in Cedral weatherboard (cement board so non combustible?) if that helps and I could use pink plasterboard inside when it gets to that stage.

I'm sure I have heard other people say on here it is the internal floor space. Feel free to chip in on this if anyone knows for sure.
8.6 x 4 would give 34.4m2 external size (I may have to reduce this a little for roof overhangs and external baton/cladding etc).
Assuming 150mm timber frame that would reduce the floor size by around about 4m2 (my very quick rough maths on that one).
I should end up with pretty much 30m2 internal maybe a bit less.

Yes I will be insulating between the frame but my plan is to leave the inside mostly unfinished for now (storage for my tools and windows, fascias etc) and use up insulation left over from other jobs as and when it comes in. I will also put out a heads up to my builder friends that if they need rid of any just drop it on my drive.
I think you are correct... though with 150mm walls you are still over

8.6 - 150 - 150 = 8.3
4 - 150 -150 = 3.7

3.7 * 8.3 = 30.71m2

Though like you say you could have a bit for the roof overhang.
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Yes you're right about the floor area being internal.
The non combustible thing is just so we don't get the great fire of London again!
For houses it basically means brick, but if you're going for timber frame it usually means 60min fire board on the outside and triple plasterboard on the inside. I only know that because someone had that situation with an extension so building control were complaining.
But that's literally only for the sub 1m situation.
Yes you're right about the floor area being internal.
The non combustible thing is just so we don't get the great fire of London again!
For houses it basically means brick, but if you're going for timber frame it usually means 60min fire board on the outside and triple plasterboard on the inside. I only know that because someone had that situation with an extension so building control were complaining.
But that's literally only for the sub 1m situation.

Cool! interesting information to know.
Triple plasterboard!!! :eek: Ive never heard that one before, Even with pink plasterboard?
I think the important thing is that both sides have adequate fire resistance, the exact means is down to you and the bco. Basically if there's a fire inside, they don't want so much heat to escape through non fire proof areas that it goes across every house in the road one by one. So each house has a fire break on the boundary.
If you're really close, they want the inside to be protected too, otherwise the wall might collapse then you'd be in the same situation anyway with a burning inferno right on the boundary!
My shed is coming along and is water tight finally.
Questions about insulation?

I am leaving the roof for now. Will insulate it at a later date using up offcuts from jobs.
Ceiling I have used 25mm celotex (tuck taped) and 15mm pink plasterboard under the joists and I will fill between the joists with wool insulation and then board over.

Just need to decide on the walls.
150mm timber studs OSB and breather membrane outside (to be battened out and cladded).
Inside I will vapor barrier and finish off with 10mm insulation backed plasterboard.

What should I do between the studs?
1. Full fill with ridged insulation?
2. Partially fill with ridged insulation (100 or 120mm)
3. Full fill with wool insulation? Cheapest and easiest option but is the U value alot lower than rigid?

I am going to partition out an office in here so would like it to be nice and warm


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