Foundations for steel framed workshop?

[Hooflungdung]

I am planning to build a steel framed and steel clad garage and workshop next to each other on the same slab. I want to build them within permitted development contraints and they are closer tha 2m to a boundary so can only be 2.5m high overall. I am building this myself, not from a kit.

What I am struggling with is what I am going to build it on. Looking around various builds on the interenet it appears that a reinforced concrete with a minimum thickness of six inches is fairly standard. What is less clear to me is whether the slab needs to be increased in depth all around the perimeter, as with a standard bricks and mortar build, or just thickened locally under the building's supporting pillars. In effect forming a series of pads integral with the main slab.

Any advice gratefully received.

 

[Erie Fred]

Where is the columns coming from ?
Purchased or your own design ?

 

[Wildefalcon]

When I did mine, Council building control required a concrete pad one metre cubed for the pillars. They came and inspected the holes prior to the concrete pour.

Clay soil, former mining area.

They also required an engineering opinion as to what pads were adequate.

Talk to to the Building Control people.

 

[Agrismith]

Poor the pads the columns will sit on and leave them at the height of the underside of your slab. Build the building then poor the floor slab around the columns. You then aren't held to weather constraints and will end up with a better finished product. You also won't have base plates and bolts in your new workshop floor.

 

[wyn]

Why two lots of columns down the middle? Or are they separate?

 

[Bobtail4x4]

start from basics, what is the ground type? clay? sand? wet claggy stuff?

btw PD is planning, they still will need Building Regs.

 

[gaz1]

I am planning to build a steel framed and steel clad garage and workshop next to each other on the same slab. I want to build them within permitted development contraints and they are closer tha 2m to a boundary so can only be 2.5m high overall. I am building this myself, not from a kit.

What I am struggling with is what I am going to build it on. Looking around various builds on the interenet it appears that a reinforced concrete with a minimum thickness of six inches is fairly standard. What is less clear to me is whether the slab needs to be increased in depth all around the perimeter, as with a standard bricks and mortar build, or just thickened locally under the building's supporting pillars. In effect forming a series of pads integral with the main slab.

Any advice gratefully received.
View attachment 523874

becareful if you are under 2m away from the boundary its not 2.5 in height its 2.5 at apex point whilst the closest point to the boundary is under 2.5 in height

 

[Hooflungdung]

Where is the columns coming from ?
Purchased or your own design ?

Own design.

Why two lots of columns down the middle? Or are they separate?

Two separate buildings each under 30 square metres. Both garages, although one will be used primarily for restoring a couple of cars, the other for storing the cars when they aren’t being worked on. Virtually no gap between them. Constrained between a property boundary on the rear and the long side and an existing building on the shortest side.

start from basics, what is the ground type? clay? sand? wet claggy stuff?

btw PD is planning, they still will need Building Regs.

Clay. Happy to be corrected but as I understand it, if they are under 30 square metres and built of substantially fire proof materials, no building regs are required.

becareful if you are under 2m away from the boundary its not 2.5 in height its 2.5 at apex point whilst the closest point to the boundary is under 2.5 in height

The maximum height is 2.5m dropping to 2.1m at the eaves on the boundary.

Poor the pads the columns will sit on and leave them at the height of the underside of your slab. Build the building then poor the floor slab around the columns. You then aren't held to weather constraints and will end up with a better finished product. You also won't have base plates and bolts in your new workshop floor.

That’s an interesting approach. I have seen that done on larger buildings. Food for thought.

When I did mine, Council building control required a concrete pad one metre cubed for the pillars. They came and inspected the holes prior to the concrete pour.

Clay soil, former mining area.

They also required an engineering opinion as to what pads were adequate.

Talk to to the Building Control people.

The soil is clay but not a mining area. How big was your building?

 

[Gareth J]

Would you get away with a bolt down structure being classed as "temporary" and therefore not need BC? If so, might save the hassle of building two separate but touching sheds.

 

[Hooflungdung]

Would you get away with a bolt down structure being classed as "temporary" and therefore not need BC? If so, might save the hassle of building two separate but touching sheds.

Where I am, a temporary structure is marquee or similar tent like structure. The separate sheds are compromise but one I think I can work with. I did have planning for a larger single building but one of the conditions was that it must be built of natural stone to match the main house and surrounding buildings. I simply can’t afford to build it.

 

[Welderpaul]

I've built a few such structures and i think what you are essentially asking for is a foundation design?

As far as I know Building Control won't tell you what foundation to build, they function as a checking facility to make sure you are building in accordance with a specialists design, and standard building practices.

When I have needed foundations designing I have employed the services of a structural/consulting engineer who have carried out a fairly basic site investigation i.e trial holes to establish what the soil conditions are, then designed based on that. Effectivness of design also comes into it - in some cases I have formed slab founds with local thicknening to resist column punching loads, or where the slab would be very thick, seperate pads and a thinner slab over the footprint. The Engineer will also want to know, or carry out calcs for themselves, what loads are imposed onto the foundations from the structure.

No one can say what foundation is required without a full understanding of the ground conditions. Building Control always sent someone out to verify we had excavated as far as we should, and that the expected strata had been found.

 

[Erie Fred]

As well as the vertical loads into the column foundation, there might be, based on your column design
horizontal loads that must be taken into consideration.

 

[Hooflungdung]

So, essentially, I just need to ensure that the foundation is built to the spec supplied by the structural engineer. I am leaning towards using an established groundworks firm to provide a solution.

As well as the vertical loads into the column foundation, there might be, based on your column design
horizontal loads that must be taken into consideration.

This is where I assume the perimeter ring beam solution may be better. However, the only place I see it being widely used is in the US. In the UK pads seem to be the norm.

The frame will be of the rigid portal type (welded) and I may use a centre prop, so horizontal sheer loads should be minimised.

 

[KaneH]

Pad and strip foundations for the under build with separate floor slab. Using a continuous slab between the two buildings will be a nightmare to keep the water out.

Central prop on a portal frame does little to the lateral load at foundation level. They’re more used to reduce the rafter size on larger spans so you’ll need account for this in your base / foundation design. You’ll also need vertical bracing on the longitudinal direction if it’s just a steel clad box you’re building.

I would be surprised if your local authority would accept the proposal as being two separate buildings given their proximity and size though. Best seeking advice from local planning before sinking a load of money into them. A pre-app can be useful for these type of things.

 

[Neilj]

Two separate buildings each under 30 square metres.

Happy to be corrected but as I understand it, if they are under 30 square metres and built of substantially fire proof materials, no building regs are required.

I may be wrong here but I thought it was 30m2 total area to be under the limit for building regs (plus the other stipulations as mentioned)? What's the combined area of both of them?

 

[Bobtail4x4]

Would you get away with a bolt down structure being classed as "temporary" and therefore not need BC? If so, might save the hassle of building two separate but touching sheds.

temporary is something that is there under 28 days,

 

[Bobtail4x4]

I may be wrong here but I thought it was 30m2 total area to be under the limit for building regs (plus the other stipulations as mentioned)? What's the combined area of both of them?

as long as each one is wholly detached, then two buildings each under 30m2 floor area, can be exempt,

 

[Smallfry]

Not sure about this, but do you have to have BC involved if there is any electrical supply, even if the building itself is exempt ?

 

[Hooflungdung]

I may be wrong here but I thought it was 30m2 total area to be under the limit for building regs (plus the other stipulations as mentioned)? What's the combined area of both of them?

30m2 for each building. There are two of them. They won’t rely on each other for enclosure or support. I got the idea from a self-build site with building inspectors on the forum. I have since noticed there is another thread on here where the same thing is mentioned.

 

[Hooflungdung]

Not sure about this, but do you have to have BC involved if there is any electrical supply, even if the building itself is exempt ?

Not if you use a registered electrician. Otherwise, yes, the electrics will need BC approval.