Suitable base for 8 x 6 greenhouse ?

Hi, I've got a Halls Supreme 8 x 6 that I've taken with us the last two times we've moved house. The previous houses both had solid bases on which to place the greenhouse - one, a large patio, the other an old concrete base of an outhouse. I made a simple wooden base frame from 2x2 treated timber and screwed the greenhouse onto that for the previous gardens. This time, we have nothing like that - only lawn.

I'm wondering if I can get by with just placing the wooden frame onto the soil, rather than making anything more complex / permanent, as we're renting and I don't really want to be pouring concrete etc. I'm a very amateur gardener on a very limited budget, and to be honest, if it's going to involve anything much more than what I've done previously then I might not bother.

I've googled and found lots of ridiculously complicated base plans involving half of B&Q's stock, and I can't help wondering why ?? It's only a metal frame with glass in. It weighs a ton, so it's not likely to lift off in a stiff breeze, so why all the crazy complicated bases ?

 

I agree anchoring it down and at the same time stopping the base sinking unevenly are the main problems.
Uneven sinking could result in broken glass.

I,m thinking of putting one on my allotment and its only getting a base made from 4x2, but I intend driving some spikes in the ground here and there to make it all stable.

 

....and so that nobody nicks it.

Agree with Pete.

As you are putting it on turf, I would kill this off and put down some membrane fabric. Landlord might want you to make good the lawn when you leave though

 

If you want to get a rough idea of what the wind load on a greenhouse is here is a formula -

1 - Square the wind speed and multiply by .00256
2 - Multiply the above by the square footage exposed to the wind
3 - Multiply the last result by the coefficient of drag which will be 2 for a flat plane surface.
The final result is the wind load in pounds.

So for a wind speed of say 70mph (which is maybe a slightly conservative max anticipated speed.
( 70x70 ) x .00256 = 12.544
Assuming the 8' long greenhouse has a height of 6.5' the surface area will be 8x6.5 = 52 square feet. Multiply 52 by 12.554 = 652.88
Multiply 652.88 by 2 (the coefficient of drag) = 1304.576 pounds wind load or about 100 stones ( or four very heavy chaps trying to push it over!)

This is a very rough method of calculating the wind load on a flat surface. An accurate calculation involving a 3 dimensional structure would be quite a bit more complex. However for the purposes of arriving at an approximation of wind load on a greenhouse the above formula is not far from the mark.

 

I've always found old paving slabs or reasonably sized parts thereof excellent for use as a base. The important point is getting the base exactly level using a straight edge and a spirit level. Check end to end, side to side and across the corners. This stops the frame from distorting, which otherwise could make it difficult to fit the glass. If you're concerned about the effect of the wind, though the glass should be heavy enough to stop it blowing over unless it's a strong gale, drill two holes per side through the base into the slabs and fix with screws and plasplugs. That'll stop it sliding about.

 

A sturdy foundation helps with frost heave or waterlogging. If a section of the paving slabs shift up or down independantly it can cause the frame to twist. It doesn`t take much to break glass.

Dave, as well as being pushed over, greenhouses have to resist being sucked from the ground by the wind passing over the top :wink:

 

In Scotland that's known as the 'sook effect' as opposed to the 'blaw effect' :D:D

(Spent a fair bit of time calculating wind load on various antennas, mainly to see if my rotators would handle them)

 

sook or blaw, getting 1.5 tonnes of conny airbourne will take some doing

 

Thanks for all the replies. I've hit another problem though... I've just spent the afternoon stripping the turf off the area where I'm putting the greenhouse, and the ground isn't level - it slopes off to one corner by about 4 or 5 inches. I had thought I could just dig the opposite corner down and that would be enough, but it looks like if I do that then the bottom of the greenhouse in that corner will be a couple of inches below the surrounding lawn, which means the door track will fill up with dirt on a daily basis !

I'm beginning to think that I have no option but to build up with hardcore, cement and either bricks or breeze blocks so that the whole base is above lawn level at all points.

Unless.... I could just get away with dropping a single layer of breeze blocks into a bare soil trench and put it on that.

Or.... I could just rearrange the soil back so that it all follows the natural contours and just chuck the greenhouse on that - and just have a wonky, leaning greenhouse. :skp:

p.s. - do you think compacted cockle and mussel shells would suffice for hardcore ? We have a shellfish processing factory nearby that has mountains of the stuff.

 

Hi,

I bought a greenhouse, in 8x6, from Norfolk Greenhouses, so it's only one of the cheap, bolt everything together and hope for the best models, but I just dug slightly down and skimmed with the spade to make it flat, then put paving flags (3x2) on this, and bolted to them. I'd try and dig a flat and level base, even if the lay of the land looks wonky afterwards, you can always dig the outsides to make it look more level.

 

Best option, worked for me for twenty years. If the ground is reasonably compacted after digging out, 3X2 paving slabs aren't goint to shift as long as they are level and the weight will be distributed along the length. Never had a paving slab crack.