Garden shed base - lay concrete directly on the grass?

[larrylamb9]

Hi all - a newbie here with a no doubt silly question! My builder (doing an extension) has suggested to me that the easiest and cheapest way to create a base for our new 14x8 foot shed is to cover the plot in plastic film, build the shuttering to the correct level, then fill with concrete from a mixer. No need to dig down (lots of roots) and no need to use hardcore. Sounds simple - is he right?

PS, he is a very experienced and high quality builder, but knows we are on a tight budget and so has suggested this budget method.

 

[r896neo]

At the very least you must dig off the grass and a few inches of topsoil. it will just rot and sink.

On decent ground you could probably get away without a sub-base for a little 8x6 concrete base.

But a base as big as 14x8 is almost certain to crack and fail as it settles if it has no sub-base or reinforcing mesh.

To be honest though 14x8 is a pretty large shed and probably not cheap so why shorten its life with a crap base.

If money is tight perhaps you could dig out the base and do some of the donkey work.

 

[larrylamb9]

OK, but our house was built with no foundations (1800s) except foot wide thick-looking slates/wide bricks, and that hasn't subsided (much!), so why would an area of 14x8 subside? I don't get it.

 

[leeco]

I don't think they built the house on grass.

 

[wrathkeg]

this might help

http://www.pavingexpert.com/subbase.htm

 

[r896neo]

Well clearly you know best. Go nuts

 

[leeco]

Oh yeah I forgot to say we don't live in the 1800s where they didn't have concrete or electric and stuff we live in the year 2000s

Are you going to build the shed out of asbestos like they did in the 1800s too?

 

[Trazor]

If you are determined to use this method at least use Rebar.

 

[larrylamb9]

this might help

http://www.pavingexpert.com/subbase.htm[/QUOTE]


brilliant links, thanks

 

[larrylamb9]

I don't think they built the house on grass.

they dug down about 5 inches and did not use hardcore... laid straight on the soil.

the house weighs a lot more than a wooden shed, so I was wondering why that is ok on its very small footprint of ground, but the base for a comparatively light shed on a very large area of footing needs such hard work with reinforcing or compacting etc.... thats all... just wanted some facts....

 

[larrylamb9]

Well clearly you know best. Go nuts

This is a forum, people ask stupid questions because they join a forum to learn and understand stuff. Your's is a trolling remark... go nuts yourself

 

[r896neo]

Fair enough and sorry for the remark.

I was in a bad mood after a long day and sometimes it is very frustrating when you freely offer your hard earned advice and experience only to have a poster turn around and seem to disregard it.

It's often too time consuming to explain the ins and outs of why to do something a certain way and i tried to summarise by saying the grass would rot and sink.

You don't know how your house was built and it is foolish to presume they just scraped off a few inches. The ground levels may have drastically changed over the years to make it appear this way but its almost certainly not the case. Also you would never use hardcore under a wall footing but many older houses were built with wider brick foundations to spread the load a little.

A large slab will span over a wide area and the larger the area the more likely a spot somewhere will settle differently to another spot and thats why its more likely to crack. By excavating and installing a sub base you create an even area which spreads the load and reduce settlment.

On a side note i'd perhaps re-assess your opinion of this builder as very high quality if he is suggesting this method without even removing the grass.

 

[JulianP]

I've done a few bases for workshops, normally very thick to take track laying plant etc. My theory is that you work out the cost of the excavation/sub-base/ compactor etc and use that money instead to buy yourself extra concrete thickness. It's easier and if you excavate down to find a sound base then you're OK to go straight in with concrete.

Probably not conventional wisdom but I've been OK with it!

Julian

 

[powerst]

Will probably be shot down on this idea and your size of shed may be a bit big for this but here it is for what it's worth...

When I moved and took the kid's wooden playhouse with me I dug holes and concreted in 4x4 posts and then attached 2x6 (maybe 2x4, can't remember) to these with coach bolts. Basically it was a decking frame which I then laid the playhouse floor onto.

All nice and solid and was easier than digging out and laying concrete. Not sure what the cost difference is though, it was just quicker and easier for me.

 

[Gibbo84]

Oh yeah I forgot to say we don't live in the 1800s where they didn't have concrete or electric and stuff we live in the year 2000s

Are you going to build the shed out of asbestos like they did in the 1800s too?

Even the Romans had concrete and the first battery was invented by Volta in 1800.