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Thread: Allotment greenhouse build options & considerations

  1. #17
    Chris Hulme is offline Seedling
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    Concrete I believe will be stronger, light weight seem to detriate quicker.
    Use the same mortar between the blocks, easy to do, just buy a cheap trowel from a diy store or screwfix , toolstation etc.
    A bed of a few inches should be enough.
    Forage420 likes this.

  2. #18
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    Update

    Hi everyone, so it's been just over a month since I posted this thread. I didn't quite proceed as I said I would here as I've had conversations with friends about how to go about building this and was lead to believe I would need to go quite deep as per the photo attached.

    There are a few problems in my way that I don't know how to resolve at the moment, as follows :

    1) the site slopes downwards, looking at the photo, from right to left. It is much shallower on the left side (about 250mm deep), the right hand side is about a foot and a half deep.

    2) I've been told not to use concrete, however, I'm hoping to get around this by laying concrete blocks in the trench on a bed of lime cement which I'm told is not as strong. The reason it can't be cement is because there is an allotment policy that says that foundations should be easily removable, i.e. not concrete. I'm very stuck now about what to do next.

    3) due to the slope I will need a significant number of brick courses just to bring everything up above ground level. I'm unsure how to actually build with brick, but it has to be brick because concrete blocks above ground level would not be acceptable to the committee here.


    While researching more I found this video on youtube : https://www.youtube.com/watch?v=iZdIUx3NKtg . This is clearly a professional gardener. He has used blocks laid down on their sides and encased in cement. He has built quite a few courses above the concrete block, however, he has used aggregate in the mix that the blocks sit in. I was hoping I could achieve this but with a lime mix instead.

    I think it's almost at the point now where I should think about calling in a landscape gardener to build the foundation and brick course and leave me with a timber sole plate that I can just screw the greenhouse to.

    I am sorry for being hesitant and back tracking on advice already given me here, but I'm really not sure how to proceed now. Does anyone have any more advice they can share to help me move forward?
    Attached Thumbnails Attached Thumbnails Allotment greenhouse build options & considerations-img_20190221_163159903.jpg  
    Last edited by Forage420; 21-02-2019 at 04:24 PM.

  3. #19
    veggiechicken's Avatar
    veggiechicken is offline Warning!! Contains Nuts
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    If foundations should be easily removable and you can't have exposed concrete blocks, are you sure you're allowed to build with bricks?
    What have other plot holders done?
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  4. #20
    Forage420's Avatar
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    Quote Originally Posted by veggiechicken View Post
    If foundations should be easily removable and you can't have exposed concrete blocks, are you sure you're allowed to build with bricks?
    What have other plot holders done?
    My friend on site poured a lime cement slab and built bricks onto it.

    As per my suggested plan, I intend to finish the blocks below ground level.

    Bricks are fine, but the bonding for them must be lime I'm told.

  5. #21
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    However you construct the foundation it must be level, if it is not the glass/polycarbonate will never fit properly
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  6. #22
    nickdub is offline Early Fruiter
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    Don't worry too much about the lime stuff or whatever - builders use cement/concrete a lot because if a wall they build gets a crack in it they are in big trouble + they tend to be v conservative re how strong something needs to be - you're not building v high so you don't need that much in the way of footings. Best bet would be chippings/gravel or similar about 3+" thick banged down hard (commercially they use a motorised whacker plate) but a sledge hammer held vertically and bashed down will do the job. Finish it up by mixing up your lime with some sand and water and trowel smooth - check with a level.

    You might want to check with the powers that be if you can use insulation blocks for the wall. they are much the easiest as they are quite durable, bigger than blocks but light to handle and you can cut them easily with an ordinary handsaw - I bought some off a bloke who had spares from an extension to do a similar job to you and paid about 1 each - massive work saver.

    Get a long straight edged something BTW to act as a guide when building your walls, if you don't do much building work - the professionals use twine stretched tight, but its a bit of a bugger to set properly, if you're not used to it

  7. #23
    Stan79's Avatar
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    Have you thought about a timber base instead? Railway sleepers laid on their side would be 20cm high and if you're more used to carpentry that might be a simpler option? That's what i'm planning on for mine when i get around to putting it together!

    Also, because they're long, it's easy to get the whole length level with sleepers. A gravel base in the bottom of the trench might help with drainage and should definitely help with levelling up. If you've got friends on the plot they can help you lift them!

  8. #24
    Forage420's Avatar
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    Quote Originally Posted by nickdub View Post
    Don't worry too much about the lime stuff or whatever - builders use cement/concrete a lot because if a wall they build gets a crack in it they are in big trouble + they tend to be v conservative re how strong something needs to be - you're not building v high so you don't need that much in the way of footings. Best bet would be chippings/gravel or similar about 3+" thick banged down hard (commercially they use a motorised whacker plate) but a sledge hammer held vertically and bashed down will do the job. Finish it up by mixing up your lime with some sand and water and trowel smooth - check with a level.

    You might want to check with the powers that be if you can use insulation blocks for the wall. they are much the easiest as they are quite durable, bigger than blocks but light to handle and you can cut them easily with an ordinary handsaw - I bought some off a bloke who had spares from an extension to do a similar job to you and paid about 1 each - massive work saver.

    Get a long straight edged something BTW to act as a guide when building your walls, if you don't do much building work - the professionals use twine stretched tight, but its a bit of a bugger to set properly, if you're not used to it

    Due to the slope I may need to build 3 or 4 brick courses high and intend to use bricks without frog as per the video I linked.

    Chippings/gravel lying in the base of the trench makes sense, but this would mean I need to dig out more of the trench at the shallower side as it is only deep enough for one concrete block with a somewhat shallow bed of cement.

    I've just had a look at the aerated concrete blocks you mentioned but a lot of the ones advertised through the main DIY stores have very poor reviews, with many people saying they are not suitable for foundations. They appear to be more than twice as expensive as ordinary concrete blocks.

    I might get someone to build the brick work for me.

    Any further thoughts?

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