What Thickness for Each Layer of my Shed Foundation

[WoOt]

I’ve reclaimed a concrete sectional garage, and plan to rebuild it as a shed. The shed dimensions are likely to be 3m by 6m. Each panel is 60cm wide by 1m high. So I’ll be using two panels to get to my full height of 2m.

The shed is at the back of the garden, with only a narrow 80cm access path, so it will never be used to story heavy equipment such as motorcycles or cars. I intend to use it to store my tools and bicycles.

My question is what thickness I need for each layer. I know that due to the weight of the concrete sectional panels I need a concrete foundation. I found some examples, but got confused as to whether they were talking about the full thickness, or just the thickness of the concrete itself. Obviously on a budget, so would prefer to keep the concrete to a minimum.

 

[London Mike 49]

This site is very good, loads of info http://www.pavingexpert.com/concrete.htm

Good luck
Mike

 

[WoOt]

Hi Mike, I looked at it, but couldn't figure out what thickness I needed for the concrete and hardcore. Plus most information is for people who will use it for storing cars etc. Mine is for lighter use, so I thought there might be a difference there too.

 

[r896neo]

I would use 3-4'' of compacted hardcore and then a 4'' thick slab of concrete. I would also dig out extra around the perimeter and let the concrete be 6'' in those areas, just to form a 300mm wide channel of thicker concrete under where the walls will sit. Your slab must extend past the walls by at least 6''

 

[WoOt]

Thanks r896neo.
Any other advice out there? I was hoping to go slightly thinner.

 

[Brigade77]

Thanks r896neo.
Any other advice out there? I was hoping to go slightly thinner.

Would any advice with thinner thickness's be worth it?

r896neo has it about right.

If you wish to go thinner then go ahead it's your shed, but before you do . . . ask a few qu's about working with thin concrete & how to prop up the walls when they move & the roof starts leaking !

 

[WoOt]

Would any advice with thinner thickness's be worth it?

Everyone has their opinion and most threads are full of contradicting advice. I understand the importance of getting this right, so am hoping to gather a little bit more feedback before I go ahead based on the advice of a single person. The value in a place like this is utilizing the wisdom of the crowd.

r896neo has it about right.

I’m looking to get it absolutely right.

 

[Brigade77]

I’m looking to get it absolutely right.

Then you need to understand the nature & the physical properties of the materials involved.

The 3" to 4" of compacted hardcore, I'd use at least 4" of type 2 MOT or 3" if putting down a layer of broken rubble first. A 2" layer of compacted hardcore may as well not be there as it will never interlock properly so it cannot do the job it's intended for.

The MOT layer is the foundation for the concrete. The concrete needs to be at least 4" thick because a 2" layer of concrete needs specialist materials & specialist methods of laying it, that is if you ever want to walk on it or expect it to still be sound after 6mths .

600X1000 panels from sectional concrete garages weigh a lot & if you plonk them on top of a 2" layer of concrete that's on top of 2" of hardcore then they'll crack that concrete & move a few inches, which will totally muck up the roof . . . and the door will either never open or ever close properly again.

It's your shed, it's your choice.

 

[WoOt]

Thanks Dork Lard. Where does one find Type 2 MOT? I can only seem to find MOT 1 form Wickes. Which is quite expensive.

 

[Brigade77]

Thanks Dork Lard. Where does one find Type 2 MOT? I can only seem to find MOT 1 form Wickes. Which is quite expensive.

Tell us where you are . . . we'll all come 'round & dig it out for ya !

 

[WoOt]

Hampshire, around Portsmouth. Did a Google search and found type 1, but not type 2.

 

[r896neo]

Type 1 is fine for what you need. type 2 is the same thing but a larger max aggregate size, its more often used for deeper fills and its a buggar to properly compact without a heavy duty vibrating plate or vibrating roller.

Concrete any thinner than 3'' will crack, you could use 6'' around the edges and 3 in the middle but for an extra inch its a big risk.