Forum home Tools and techniques

Greenhouse Perimeter Base - Concrete Blocks

Hi all,

I've bought a 10x8 glass greenhouse (simplicity Shrewsbury) and need to prepare the base.  I'm planning to lay a single course of concrete blocks side on as a perimeter to fix the supplied aluminium base to.  The idea being  to gain a little height  My question is, do I need to lay concrete footings?  The soil is firm and free draining so I was thinking of just laying 150mm or so of compacted MOT Sub base and then laying the blocks on a 50mm bed of mortar.  Is this likely to be strong enough and easy enough to get a good level?  Any advice much appreciated!


  • pete636pete636 Posts: 5
    I was thinking of using standard size blocks 440x215x100 standing on the 100mm side.

  • wild edgeswild edges The north west of south east WalesPosts: 8,873
    Personally I'd price up using recycled plastic instead. Something like this
    and don't forget to work out how to make a removable section for the doorway (including the lower door runner rail) if you ever want to get a wheelbarrow or sack trolley in there.
    Tradition is just peer pressure from dead people
  • StevedaylillyStevedaylilly Posts: 1,087
    edited March 2020
    Personally, I would lay a footing all round just to be safe with the loading from the greenhouse. Basically, you’ve got to take in consideration additional loading for weather ie: snow cover. You may also need to a lay a concrete hatching to the edge of the blocks, both side to add strength.
    However, wild edges suggestion of timber sleepers would not need a foundation to lay them on just compacted sub structure
    What are you going to use for the floor of the greenhouse ?

  • pete636pete636 Posts: 5
    Thanks for that.  The timber/plastic sleepers work out pretty expensive for a greenhouse this size.   I'll lay a proper concrete footing for the blocks I think.  I'm planning to put gravel over weed suppressing fabric for the flooring.
  • StevedaylillyStevedaylilly Posts: 1,087
    edited March 2020
    Have you laid blocks before ?

    Only asking because I made a small store area at the rear of my garden out of concrete blocks that was only 2 blocks high. I’m no bricklayer and you may have that skill anyway.
    But to get your levels right for the block work you will need to run a string line. I did mine by levelling 2 blocks at either end, then from those level blocks run your string line from one to the other. You might be a class A bricky so forgive me if preaching to someone who already aware of that fact 

  • KiliKili Posts: 1,019
    edited March 2020
    Why bother with the blocks. I just dug a trench the size (12 x 9) of the greenhouse. Got bags of ready mixed concrete from B&Q and poured in 6 inches. Once dry bolted it to that, never moved since.
    I slabbed the inside of my greenhouse. I dug out about 6 inches of soil and shoved about a ton of sand down then dry laid the slabs, some old slabs I managed to acquire from a bloke taking them up down the road which I noticed as I was passing. He was happy to get rid as he dident have to go to the dump. Works fine any water just drains between the slabs which don't move as the whole is held in by the concrete rim base.

    If you are going to lay blocks I would say you will need a concrete base of at least six inches . Just spreading your muck straight on a hardcore base is not something I would recommend. If you are going to do that you will need a thump plate to compact the hardcore before laying your muck for the blocks.


    'The power of accurate observation .... is commonly called cynicism by those that have not got it.

    George Bernard Shaw'

  • PalustrisPalustris Posts: 3,994
    For one of the 12 greenhouses I have built of the years, all I did was to lay concrete blocks on their side on well trodden down soil. Similar green house to yours put on top, never moved in the 25 years we were in that house. I did put a well=preserved timber frame on top of the blocks which the greenhouse actually sat on.
  • LynLyn DevonPosts: 21,138
    Ive got one on concrete blocks  straight on the ground,  as you said, makes more headroom and my dad was tall, been like that for 33 years now. Another is on patio slabs, can’t think offhand what the other one’s on, I think concrete blocks as well. 

    I have never needed to take a wheelbarrow in any of them but you could lay a board and run it up that if you needed too. 
    Gardening on the wild, windy west side of Dartmoor. 

  • Allotment BoyAllotment Boy North London Posts: 5,836
    Lyn said:
    Ive got one on concrete blocks  straight on the ground,  as you said, makes more headroom and my dad was tall, been like that for 33 years now. 

    This is exactly how I have my allotment greenhouse.
    AB Still learning

  • PalustrisPalustris Posts: 3,994
    The door on everyone of the greenhouses I have had, is not wide enough for a wheelbarrow to fit through. Least ways not the wheelbarrows I have ever had.
Sign In or Register to comment.