Garage on slope

blackbox

Not sure if I should post here or in Construction & Planning.

I want to install a Steeltech/Adman type garage but the site has a steep slope downwards from front to back.

I'm thinking about building block walls on the sides to bring the lower end up to the front level and then spanning them (4 metre span) with hollowcore or similar. It needs to support a vehicle so I don't think wooden joists would suit. The floor will give me some additional storage space beneath it for gardening stuff (access from the back).

I'm having difficulty getting a response from hollowcore suppliers for pricing and availability. Any recommendations?

Is this the best way to go or should I be considering a different approach?

Calahonda52

So are you planning to build the foundations in line with slope and then build triangular shaped block walls, which will then be loaded with HC and a vehicle.
And you are the going to be able to walk in at the back under the HC.
.
If so, it is downright dangerous, IMO

blackbox

Calahonda52 wrote: »

So are you planning to build the foundations in line with slope and then build triangular shaped block walls, which will then be loaded with HC and a vehicle.
And you are the going to be able to walk in at the back under the HC.
.
If so, it is downright dangerous, IMO

The walls wouldn't be triangular or they might slip down the hill - will be in one or two steps.

Why would it be dangerous if floor is rated for load?

TheW1zard

Just build it up and build flat. Bit of landscaping!
What your describing wont last i reckon

mickdw

Should be fine with proper foundation built level or stepped.
Walls need to be of suitable width also to avoid buckling issues. You could add some further piers etc to support walls.
Hollowcore company will design the slab but will generally require details of any special loads being applied to floor.

Lumen

What's the height difference?

dubbrin

mickdw wrote: »

Should be fine with proper foundation built level or stepped.
Walls need to be of suitable width also to avoid buckling issues. You could add some further piers etc to support walls.
Hollowcore company will design the slab but will generally require details of any special loads being applied to floor.

This ^^

Proper foundation + proper wall + proper slab + shed = right job

Don't mind any of the rest, once it's done properly you're away. Ask someone in the know to specify the width and depth of foundations. Ask them to specify the wall size and any extra piers as above. A hollowcore slab company can deliver and position. The shed company will build on this as long as the size is right so consult them early. You'll have gaps in the floor to underneath if you don't pour a finish screed though.

Lumen

dubbrin wrote: »

You'll have gaps in the floor to underneath if you don't pour a finish screed though.

That could be a handy feature.

Calahonda52

blackbox wrote: »

The walls wouldn't be triangular or they might slip down the hill - will be in one or two steps.

Why would it be dangerous if floor is rated for load?

Its not just the floor, its the walls, foundations, soil propensity to shear when wet etc etc.
Stepped foundations might be better but they need to be keyed like retaining walls.
As suggested earlier, a bit of cut and fill and approved hardcore

blackbox

Calahonda52 wrote: »

Its not just the floor, its the walls, foundations, soil propensity to shear when wet etc etc.
Stepped foundations might be better but they need to be keyed like retaining walls.
As suggested earlier, a bit of cut and fill and approved hardcore

The front one third of the garage will be on ground that is already level. I reckon I'll have to build a retaining wall across it to prevent slippage of this part. Deepest point is less than 2m.

After the garage is installed I intend to put in a dampcourse and screed.

I had considered building two sections with a gap between them that I could use as a garage pit, but I would probably get more value out of the storage space.

listermint

2 meters is alot. I had assumed the slope was only slight.

TheW1zard

Build a wall on the back side, making sure your foundation is in solid ground. Build the two side walls.
Fill it in. Mesh and 150.

Mr Tickle

blackbox wrote: »

The front one third of the garage will be on ground that is already level. I reckon I'll have to build a retaining wall across it to prevent slippage of this part. Deepest point is less than 2m.

After the garage is installed I intend to put in a dampcourse and screed.

I had considered building two sections with a gap between them that I could use as a garage pit, but I would probably get more value out of the storage space.

Just put something heavy in the front third.

blackbox

TheW1zard wrote: »

Build a wall on the back side, making sure your foundation is in solid ground. Build the two side walls.
Fill it in. Mesh and 150.

I've considered that but I'd like to make use of the space underneath.

listermint

blackbox wrote: »

I've considered that but I'd like to make use of the space underneath.

You won't use the space underneath.

Concentrate on making it safe to carry the weights your talking about . Leave the space underneath to dreamers.

TheW1zard

Its not slippage your stopping, its subsidance.
Your garage will settle over time.

TheW1zard

Your best bet is to build two walls with strip foundations. One at the start of the slope and one at the back. Then your side walls. Then fill the slope in (in between the two strips)
Then mesh screed etc

mickdw

What the op is proposing is not rocket science.
Yes, it needs professional input but is not a big ask.
A plot with a slope that will allow a walk in inspection pit that can freely drain out the open side sounds to me like too good an opportunity to turn down if you are into such things.

TheW1zard

With enough money and rc anythings possible

Lumen

I assume it is your intention for it to be planning exempt, or you wouldn't be asking in a DIY forum.

You need to calculate the effective height for planning. It's really a question for the Construction and Planning forum, but as I understand it the planners take their measurement from the lowest point (technically of the site, but in practice around the structure) to the highest.

If there's a 2m elevation change, you are likely to end up breaching height restrictions for the highest point of the roof.

Which means it won't be planning exempt.

This is looking to me like a not insignificant undertaking.

mickdw

Planning while holding things back a bit wouldn't have a major cost for such a shed in most cases.

blackbox

Lumen wrote: »

I assume it is your intention for it to be planning exempt, or you wouldn't be asking in a DIY forum.

You need to calculate the effective height for planning. It's really a question for the Construction and Planning forum, but as I understand it the planners take their measurement from the lowest point (technically of the site, but in practice around the structure) to the highest.

If there's a 2m elevation change, you are likely to end up breaching height restrictions for the highest point of the roof.

Which means it won't be planning exempt.

This is looking to me like a not insignificant undertaking.

I'm on a hillside. The lowest point of the site is about 20 metres further down. The highest point (entrance gate) is probably 20 metres higher - well above the roof of the house.

The garage base will be at pretty much the same elevation as the house base. The build up to level the garage will be less than 2 metres.

Lumen

blackbox wrote: »

I'm on a hillside. The lowest point of the site is about 20 metres further down. The highest point (entrance gate) is probably 20 metres higher - well above the roof of the house.

The garage base will be at pretty much the same elevation as the house base. The build up to level the garage will be less than 2 metres.

Right, but with a pitched roof you're limited under exempted development to 4m to the ridge (3m with flat roof), so I can't see how you can do this without planning permission.

In theory you can raise the level of the ground up to 1m without planning, but then you're really into the weeds of interpretation of planning laws.

mickdw

Lumen wrote: »

Right, but with a pitched roof you're limited under exempted development to 4m to the ridge (3m with flat roof), so I can't see how you can do this without planning permission.

In theory you can raise the level of the ground up to 1m without planning, but then you're really into the weeds of interpretation of planning laws.

I know of a section 5 that went to council 're a large flat roofed extension on a sloping site that required 1.8m height rising walls before floor level with the majority of those walls exposed externally at the lower end of the extension. Section 5 granted and drawings as submitted where pretty clear as to exposed height at all sides.
Seems planners have differing interpretations too.
I told that person not to even try for the section 5 declaration .... made me look silly.

blackbox

Job Done (at last).





I got a contractor to do the foundation.

Purgative

Looks a tidy enough job Blackbox. Good luck with it.

kil

Nice job blackbox and thanks for updating the thread. So many threads never get concluded.

mickdw

Thats not going to fall anyway.
Only thing id say is the hollowcore ends could have been hidden for a tidier finish but its a fine shed.

Pkiernan

listermint wrote: »

You won't use the space underneath.

Concentrate on making it safe to carry the weights your talking about . Leave the space underneath to dreamers.

Lol

listermint

Pkiernan wrote: »

lol

winning the internet everyday Keirno. Its Friday, go rub a cat and have some tea.

The Continental Op

Given the slope and the obvious way of getting ventilation I think I'd have had to have incorporated an inspection pit.