Foundation options for a new greenhouse

adocholiday

Hi all, I've just purchased a greenhouse and I'm looking for advice on the foundation to put down for it. It's 8' x 12' and has a light wooden frame with toughened glass. The wood is pressure treated Nordic spruce and the structure weighs approx. 600kg. I'm putting it into what's now a lawn but has poor draining, compacted soil. Is a 100mm poured concrete base my only real option because that will cost around €500 and if there was a cheaper option for it I'm all ears. One thing I'm concerned about in using poured concrete is that if we ever want to buy a bigger greenhouse or relocate this one then the concrete base is a real limitation. Would something like a 150-200mm compacted gravel base do the job here? Just for drainage etc. I'd imagine that this would be a good option? Any advice would be really appreciated.

The Continental Op

I'd put a strip foundation maybe with a single block on its side and put the greenhouse on that. Possibly reinforce the foundation with a bit of mesh or couple of 10mm bars if you don't do it too thick. I'd go down a foot and 9inch wide.

Less concrete and you keep the soil inside the greenhouse to grow plants it.

monseiur

With a water logged lawn this is not a good time of year to go at it. Best wait for a dry spell in April/May - this years crop will be a tad late but better do it once and do it right. In the meantime I would suggest that you open a deep drain from the proposed site of the greenhouse and go with the natural fall of the land.

Regarding the foundation - a strip foundation 9 inches wide x 6 inches deep will do with two or three rows of 4 inch blocks on flat on top to ensure that the timber frame will be above the level of top soil in greenhouse - otherwise the moisture in the topsoil will rot the bottom rail in no time - even it it's pressure treated. The 9 inch wide strip will give you some room to manoeuvre even if your strip foundation is a little out of square. Don't forget to run a strip of DPC on top of strip/under frame

blackbox

I put an aluminum one of that size on levelled paving slabs, but I think I'd want to raise a wooden one a little higher to stop it from rotting. 4 inch solid blocks on their side with a damp proof sheet on top would probably be ok.

adocholiday

Sorry for resurrecting this thread, but I'm going to start the foundation this weekend. I'm going to follow the advice here on the thread, going for a 6 inch deep strip foundation using a 5:1 aggregate to cement mix with a length of 8mm rebar running through the centre. Just one question though, because I have little experience in block laying, would it be a better option for me to put some wood forms in and just add an additional 100mm to the depth of the foundation? Is there a downside to that? I'm just thinking that it would be better too because I can set anchor bolts into the foundation then, rather than having to drill bolts in through the block and cured concrete after the fact. Interested to get any opinions on that.

greasepalm

Both my greenhouses are on cement base with 4" solids on their wide side and on top of them 4" on their sides giving you more headroom

and the edge of aluminium sits over it . Level and square and if you need water and power in there to make life easier for yourself.

adocholiday

https://www.boards.ie/discussion/comment/123258926#Comment_123258926

Yeah I'm good with that approach but just wondering if it would be better to just continue the concrete base up out of the ground rather than laying blocks on it. The base of the greenhouse is just a 2x4 basically and it needs to be anchored to the foundation. My concern is that my block laying skills will leave me with a poorly finished base and then I'll have to drill into it to put the anchors in. By just bringing the concrete further up I can avoid dodgy block work and won't need to do any drilling because I can set the bolts when it's poured.

beggars_bush

Neighbour poured a greenhouse base a few years ago and the best thing he then poured was a concrete shelf with an in built slope in it.

Retains the heat, plants grow faster.

He has a grape vine producing each summer (jealous) and always seems to have strawberries

greasepalm

As i got someone to do that work and with power tools made light work drilling into the blocks with plugs and screws.