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Lean to greenhouse for overwintering

cazsophieq2019cazsophieq2019 Carrickfergus, Antrim Posts: 179

This year I bought my first greenhouse,a halls lean to which I built against an old outhouse brick wall. I want to use the greenhouse for overwintering plants and cuttings however I am concerned that it will let cold drafts in as its not flush to the wall and its old an slightly uneven in parts.

It's also sitting directly on paving so not completely airtight. 

I'm planning to get gravel to put on the bottom of it for drainage and extra ground protection however I also want to seal it to keep the drafts out. 

My original intention was to purchase a standard weatherproof sealant for sealing the gaps between the structure and the wall / paving but reading differing views on the effectiveness of this so wondering if anyone would have experience or knowledge around this.

Thanks in advance for your help and feedback 🙂



  • nick615nick615 SW IrelandPosts: 1,153
    I suppose there's an unanswered question about what you plan for it next year, as this could affect what you do now?  As the greenhouse is new (to you), there'll be an element of experimentation so, to create an inexpensive draft exclusion, why not roll foam rubber in polythene (bags ideally) and place it between your uprights and the wall before screwing/bolting to the wall.  That'll keep the drafts out on a temporary basis and you can then decide on what you want to do permanently.  Cost almost nil.
  • cazsophieq2019cazsophieq2019 Carrickfergus, Antrim Posts: 179
    Thanks for responding 🙂
    the greenhouse is already attached to the wall I actually built it in May and I've been using it for bringing on seedlings which I'll be doing next year.

    However I have tender plants like French lavender strawberry plants and cuttings that I wish to over winter so this is why I'm asking.

  • nick615nick615 SW IrelandPosts: 1,153
    I understand so, if your original fixings are screws or bolts, you could slacken them off, put some sort of filler in and re-tighten or, probably more expensive, get a can of spray foam to squirt in the gaps?
  • NollieNollie Girona, Catalunya, Northen Spain.Posts: 6,073
    I would just use a standard, colourless silicone sealant in a gun to seal between the wall and the frame. I did that recently between an uneven stone wall and the aluminium frame of a mosquito screen as there were too many gaps letting the blighters in. Worked a treat.

    However, the gaps may not be so much of a bother for a greenhouse, as you don't necessarily need it 100% airtight, unless you are using heated mats and a stable temperature is critical to very tender things. Does it have louvres to open during the day? Even over-wintering plants need a little fresh air. 
  • cazsophieq2019cazsophieq2019 Carrickfergus, Antrim Posts: 179

    Thanks again for getting back to me.  @nick615 the thought of loosening the uprights from the wall I must admit fills me with horror lol, as attaching it to the wall was the most difficult thing to do, but I do get what you're suggesting .... now that the structure has been in place for a which, it might be a possibility, although tbh I'm leaning on the idea of using silicone.  @Nollie no the lean to doesn't have louvres but it has a window which can be opened and closed.  I was wondering if I'm being a tad overprotective by putting silicon around the greenhouse gaps, although where I live it does get pretty windy ..... perhaps I'm overthinking the whole thing.....

  • AnniDAnniD South West UKPosts: 10,567
    edited September 2020
    It may be easier just to buy fleece that you can put over the plants when frost is forecast. I have an upright small coldframe that isn't completely air tight when the lid is down, and just use fleece as and when required.  :)
    You could also try "slabs" of polystyrene to line the walls - l seem to recall Monty doing that on a GW programme some years ago, and l do that in my coldframe if the weather turns exceptionally cold.
  • cazsophieq2019cazsophieq2019 Carrickfergus, Antrim Posts: 179
    @AnniD thanks for your suggestion, you just got me thinking ....... :-)
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