Advice Needed For Greenhouse Base

[Mark13]

I'm after some advice on how best to build a greenhouse base. I currently have a 10 X 8 foot greenhouse on a 100 X 100 mm treated wooden perimeter base. This base is sat directly onto soil and is well over 10yrs old now. Not sure how it's anchored if at all, but the greenhouse frame is screwed into the wood which is badly rotten and needs replacing. I've been tempted to replace like for like but am now thinking of a perimeter base made from concrete blocks as this wont rot. The inside of the greenhouse will be kept as a gravel walkway and a raised bed for growing. My question regards the footings for the blocks themselves. Can I dig a trench, fill with compacted hardcore and lay the blocks directly onto that or do I need to pour a concrete strip footing. I've looked online and some info suggests a concrete footing (more expensive) and some info suggests that you can lay direct onto soil on a (semi dry mix???) as the blocks would only be 1 block in height. I figured my initial thought of using hardcore would fall somewhere in middle and give me a solid foundation on a lower budget???

[Conor]

We've had a few glasshouses at my dad's place over the years. Every one was a shallow trench, compacted fine stone, dense blocks laid on thier side, only joints roughly mortared (top of blocks roughly ground level), then a course of blocks laid normally on edge on top of this. Then glasshouse built directly on top. Never had an issue, from the 30ft cedar wood house to the current 12ft aluminium house.

[Mark13]

Thanks for the advice! I was going to tackle this project a year or so back during covid but never knew how best to proceed. Plus the greenhouse was packed with pots, garden tools and the like so I kept putting it on the back burner. Seems there's a lot of videos on YT showing how to mix mortar and lay brick and block but very few showing different techniques for foundations which is a disaster for an overthinker like me. Again many thanks 😊 

[saveasteading]

I put down a platform of rubble then gravel grids. At the corners and mid length I replaced with a paving slab to allow a screw fixing to a dead weight.

The platform is abut 100mm bigger each side than the greenhouse. So it simply sits on it.

The gravel allows it to absorb spills, and in scorching weather it can be soaked to reduce temperatures.

 

I put in a layer of geomembrane to stop weeds coming through.( Actually I used some old vapour barrier) .

 

I'd do the same again. It may move seasonally but it is totally flexible so I wouldn't know.