Greenhouse base

[Roundtuit]

I've offered to give someone a hand putting up a greenhouse that they've inherited.  I think it's about 17ft x 8ft, and they were planning to just level the garden, lay some slabs on sand and bolt down the frame to that.  I'm not keen on that idea, as a) slabs laid on sand is never a good idea (I can foresee movement and cracked glass...) and b) to do it properely with slabs (effectively build a patio to put it on) is a big job for a greenhouse that size.

 

It's only the perimeter that needs to be solid and it doesn't need to be pretty, so I'm looking for suitable, cost-effective alternative.  Could I knock up some shuttering and cast a concrete plinth?  Dig it out a bit and lay blocks on compacted Type 1?  Any thoughts please?

[NSS]

Our greenhouse is 9-sided. I cast a concrete ring-beam roughly to size/shape and then laid engineering bricks to the actual shape. Frame is then screwed into rawplugged holes in the bricks as per pic.

 

Edited October 3, 2020 by NSS

[nod]

We had a similar sized greenhouse at the last house 

I simply laid a single block on its flat side down On a bed of motar 

Then screwed the frame to the middle of the block 
It’s been down for about fifteen years and seems ok 

[joe90]

I did one recently and cast a ring beam with wire in it and bolted to that, worked great.

[Roundtuit]

I think the concrete ring beam is the way forward; what size do you reckon?  Will 20cm x 20cm do it?  Straight on to soil?  Any reinforcement required?

 

Cheers

[PeterW]

20x20 will be around half a cube of concrete so it won’t be going anywhere ..! Blocks set in a dry haunched mix may be better and quicker.