Workshop

[gwr]

Hi I am nearly in the position to have my 6.5 x 2.5 M shed dismantled and build another @ 9 × 4 m subject to planning and building concent. The access is not great and don't fancy digging trench founds by hand @ a meter deep so looks like I won't be having it built in block.
What would be the easiest founds for dwarf walls to be built off, shallower trench found or build of a reinforced concrete slab? I know the final say is with building control but I am pondering my options to put to them.

Also with it being built in timber closer than 1 meter to boundaries what does BC accept as a suitable fire retardant to paint on timber? I have seen some products that claim to be fire retardant but not sure if enough to satisfy BC.

Any advice is appreciated

 

[RobinBHM]

These days, generally trench foundations are the cheapest because building inspectors will approve them for construction, whereas all other types like raft foundations need a structural engineers design.

Foundation depth is determined by soil type and influence of trees. Shrinkable soils with trees nearby will mean very deep foundations!

 

[MikeG.]

That size means this proposed building requires building regulations approval. That means you will have to provide calculations for any raft-type structure, and these can be quite a thing, with reinforcing and reinforced "toes". They're necessarily more expensive than strip footings and a ground bearing oversite slab. However, if you are in clay, and there are trees around (even a hedge), then a raft is often a better option than strip footings say 3 metres deep.

Now, if you were to reduce the building a little, such that the internal floor area (ie measured inside the walls) was a gnat's below 30 square metres, then you wouldn't have to comply with building regs (so long as it's use was solely as an outbuilding and it was a metre from the boundary or built of non-combustible material). Then you would be able to build it however you wanted, and you could just pour a slab 100mm thick and build off that if you were building a timber framed structure. If your walls are 100mm thick then at the moment your building is 33.4 sq m. It if it were just over 900mm shorter, you would be under 30 square metres and free of the regs (which doesn't mean it wouldn't need Planning Permission. That's a different thing).

There are cementitious boards available (Eternit make one) which look like timber feather edge boards, and provide the necessary non-combustible performance.

 

[Rorschach]

I think if you trim down the size a little you won't need planning permission. If you need more space, build another small storage shed. If I have to build another workshop it's what I plan to do.

 

[RobinBHM]

I agree with Mike, avoiding building regs will save you some cost and aggravation. Although thats not to say you want to scimp on build quality, but I would assume that building regs would apply the criteria for the foundation of an outbuilding as a house build, which is likely to be uneccessary overkill.

I dont know but maybe building regs would expect structural calculations for the structure so they are satisfied it would have sufficent lateral stability and strength for roof loading including snow load. -Im not sure if these things apply for an outbuilding

Note that the 1 metre distance from the boundary for fire barrier reasons applies for building above 15 square metres, so that part of the regulation still applies.

You will also need to have a certificate for the electrics, whatever size you build since the work is notifiable.

But apart from those provisos, no other building regulations apply for the construction under 30sq metres.

However permitted development rules still apply, or you need full planning.

 

[gwr]

Hi thankyou for the advice, I had replied but it seems to have vanished! anyhow what I take from this so far is try to avoid BC to save a lot of stress which when I dig further seems good advice given I wasn't going to be massively over the 30M limit.

So if the site is dug down and about 100mm of type 1 well whacked down 50mm sand dpm then 100ml concrete Does that sound about rite?
It looks like I will still need PP as I am going to be closer than the 1 meter to boundary so I may as well try to get more height than the 2.5M and have a pitched roof and tiled or some other covering that meets the regs for fire.

Does this mean I will need full planing or could I do it with building notice?

I will check out the fire cladding thanks again folks.

 

[MikeG.]

Hi thankyou for the advice, I had replied but it seems to have vanished! anyhow what I take from this so far is try to avoid BC to save a lot of stress which when I dig further seems good advice given I wasn't going to be massively over the 30M limit.

Sensible compromise, in my view.

So if the site is dug down and about 100mm of type 1 well whacked down 50mm sand dpm then 100ml concrete Does that sound about rite?

Take a look around. Is the ground clay? Are there trees, or "made up" ground, or a hedge? Are you crossing a drain? If yes to any of that, then you might want to have some reinforcing in your concrete (A142 grid is standard off-the-shelf stuff at most merchants). If you have reinforcing, it needs to be 30 to 50mm up from the bottom of your concrete, but well below the centreline, which means you would be best going for 150mm thick slab. In perfect conditions 100mm non-reinforced concrete is fine. You don't need 50mm of sand, just enough sand to "blind" the hardcore/ Type 1 such that the polythene is protected from sharp edges.

It looks like I will still need PP as I am going to be closer than the 1 meter to boundary so I may as well try to get more height than the 2.5M and have a pitched roof and tiled or some other covering that meets the regs for fire.

Does this mean I will need full planing or could I do it with building notice?

You're confusing PP and Building Regs. Your planning application will be a "Householder"-type application and cost £172. "Building Notice" is to do with Building Regulations, not PP, and as you are going to build a non-controllable building, then the Regs don't apply (except as described previously).

 

[RobinBHM]

You need to be more than 2 metres from the boundary to have the height above 2.5m or apply for full planning.

Im never sure to address the damp proof membrane detail for a dwarf wall that sits on the slab. Id be interested to know how its detailed.

 

[gwr]

OK after much head scratching and measuring my head is sore lol.Anyway this is where my head is now, my back fence is 10M long this sits parallel with the house that is 11M from fence.

After much reading workshop builds both here and another woodworking forum I would like to build in timber off a 3/4 brick height wall.
In my opinion it looks much better for a garden build,after all the Mrs has to live here too lol.

I think I could live with the 2.5 height restriction as the shed I have at the moment is 2.5 at the highest point but around a 260 mm step up into it and 100 mm roof joists leaving a working height of 2.140.

So if I leave a 1 meter space at the back and 1 side a waste I know but I would have needed around 500mm anyway so not too much of a biggie and build either 7.5 M x 4.0 M or 7.8 M x 3.8 m I'm I right in thinking this would this neither need PP or BC ?

Also can anyone tell me what size roof joists I would need for this span?

Mike the ground is flat with no trees, if memory serves me right the soil is a little clayey (is clayey a word) but not too bad.

Finally for now is there a possibility of having a timber floor that doesn't loose me too much height in this design?

 

[Rorschach]

Remember the 2.5m height restriction is from the natural ground level, so if you dig down a bit you could give yourself more headroom.

 

[RobinBHM]

Joists, 195 x 45 4m span 170 x 45 3.4m span.

You could use the rule of thumb:

Length in feet /2 then add 2 = joist width in inches.

 

[gwr]

That would be a bonus Rorschach I can see that working with a concrete slab that finishes 50mm above ground level but not sure if this would be possible with I timber floor?

That's great Robin thanks for that info is that at 400 centers ?

 

[gwr]

Well I think I have the slab sorted! (In my head that is anyway) as the place the slab is going is under decking at the minute hopefully not for much longer I can't recall the soil being too bad.If that is the case I hope to lay a 125mm slab with reinforcement and deepend to around 300 around the perimeter.
Does this sound feasible and would I need any further reinforcement where it goes deeper around the perimeter?

I believe that No part of the build can be within the 1 meter of boundary unless built of non combustible materials! Could I build the back of the shed (7.5M long) dead on the boundary with the face and underside of roof overhang clad in fireproof board?