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Greenhouse base construction

NormandyLizNormandyLiz Posts: 788
in The potting shed
Project Greenhouse will be underway in a month or so. Excuse my dreadful painting, but downhill with a following wind it should look something like this



It's a lean-to with a reverse sloping polycarbonate roof, really because it's the only way I can get a greenhouse to fit anywhere without major (unaffordable) work. It's windy round here and the whole garden slopes, especially in the areas I'd want to put a greenhouse. This way it will be a bit protected and also screwed to the wall of an outbuilding.

But... there is a slope towards it so I need to think of the base and drainage before starting. The inside will be earth beds at the back and a wooden floor (actually an old wooden shutter), and I don't want concrete for various reason. I will level the actual site and about 1m in front of it (the doors will open out because of the slope of the roof), with a shallow step down to that levelled area. Leaving door opening space, the area around it will be planted.

My thoughts at the moment are to have the structure sitting on concrete slabs for stability, and then have a gravel gully just in front to act as a drainage ditch. I could also put a layer of gravel under the flooring.

Is this a good, iffy or dreadful plan? Any thoughts?
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  • tigerburnietigerburnie Posts: 131
    If you intend to just grow in containers that looks ok to me, if the building you are up against has a damp course remember not to go above it, you may cause problems with soil against it.
  • NormandyLizNormandyLiz Posts: 788
    Thanks for the reply, @tigerburnie. The building has no damp course, it's a barn without even much in the way of foundations, but solid enough to have a greenhouse attached to it.

    The intention is to have a 2.5m x 60cm soil bed, retained by some fabulous old barn beam sections (from a skip!). I have trestles/planks for seed trays, etc. and there will be a removable shelf on the wall. The idea is to have as much flexibility as possible in the limited space (approx 2.5m x 1.5m). 

    Against that wall never gets really sodden. Even with the deluge we've had over the past week it's got wet but never sodden. To be honest, I'm not expecting it to get badly flooded but it seems a sensible precaution to consider the (slight) slope and the possible accumulation of water during a storm (which of course we NEVER have in Normandy!)
  • FairygirlFairygirl Posts: 55,117
    Is the water from the roof feeding into a gutter - and into a water butt or similar?
    It could cause problems otherwise. You don't want excess water getting in behind the greenhouse, and making it's way into the g'house itself.

    Lovely painting by the way  :)  
    It's a place where beautiful isn't enough of a word....



    I live in west central Scotland - not where that photo is...
  • LoxleyLoxley Posts: 5,698
    It's a lovely painting, I admire the skill and patience of how you've shown the panes.

    Anyway - personally I would lay a strip foundation of concrete where the greenhouse meets the ground, and ensure the greenhouse is fixed down to it (bolted or cast into the concrete). The gravel trench on the slopeward side sounds a good idea to catch water coming down off the slope.
    "What is hateful to you, do not do to your neighbour". 
  • NormandyLizNormandyLiz Posts: 788
    @Fairygirl, the roof will feed into the gutter. At the moment there's no water butt as we have a well, but I'll not discount it in the future.

    Thanks for the thought, @Loxley. As I say, a few reasons for not wanting any form of concrete base, although I agree it would give an extra layer of security. The construction is from reclaimed doors and windows, which have a weight to them, and the whole thing will be bolted to the wall. If necessary, I have another chunk of barn beam which weighs a ton, and sections of that could be dug into the front, adjacent to the doors, bolted to that. I'll talk to Sylvain who is the technical brains as well as the brawn, and see what he thinks. 

    And thanks for being kind about my poor painting skills. I'm working on it! 
  • Nanny BeachNanny Beach Posts: 8,719
    Your painting skills are fabulous 
  • BluejaywayBluejayway Posts: 392
    That’s a fab painting!
  • NormandyLizNormandyLiz Posts: 788
    You're very kind. The perspective is rubbish, it's hard when you're making it up (and being too lazy to work it out properly)
  • DovefromaboveDovefromabove Posts: 88,147
    edited August 2023
    Painting  😊 👍 

    I’m just a bit worried that in a downpour the gutter may not be able to cope with the additional water from the roof and it would then overflow under the tiles of the barn roof potentially damaging that roof and the wall. 
    Here in ‘dry’ East Anglia we’ve had  deeper guttering put on our house as the original just couldn’t cope. 


    Gardening in Central Norfolk on improved gritty moraine over chalk ... free-draining.





  • FairygirlFairygirl Posts: 55,117
    That's what concerned me @Dovefromabove. Even a hefty shower, thundery downpour etc, could just be a bit too much. It would be a shame if there was damage caused to either building, and polycarbonate does deteriorate more rapidly than glass, with sun on it as well. I'm assuming, rightly or wrongly, that Normandy isn't hideously wet, but it wouldn't take much rainfall through winter to potentially be a problem. 
    A water butt could certainly be the answer ,and useful anyway if there's a shortage of water through summer. Worth looking at @NormandyLiz?  :)
    It's a place where beautiful isn't enough of a word....



    I live in west central Scotland - not where that photo is...
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