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Greenhouse - glass vs poly

Discussion in 'off topic' started by zippy, Sep 9, 2021.

  1. zippy

    zippy pfm Member

    My 8x6 glass greenhouse is now 20 years old. Over that time it has suffered 11 breakages all repaired with twin-walled polycarbonate. The poly repairs are lasting ok although a bit of algae inside the oldest poly panes, however I figure its time for a new greenhouse so... Glass vs poly.? Any other considerations?
    And why do they make 8x6 but hardly anyone makes 8x8?
  2. gintonic

    gintonic 50 shades of grey pussy cats

    i should say, i know nothing about greenhouses, other than i helped my Dad build his new one recently - his third in about 40 years.

    I asked him about Poly vs glass, he swears by glass even when i pointed out breakage etc.... He says glass feels sturdier due to the weight of the glass
  3. dweezil

    dweezil pfm Member

    Most of the Elite were modular so you can get any length. Their 8 foot greenhouses are actually just over 2.5m though if you're worried about fitting on an existing base.

    You can spec toughened safety glass; i'd do that anyway if you're glazing to the ground.

    I think poly lets through less light and will blow away more readily if on a breezy site.

    Check out quality carefully; you might decide refurbing the old one a better option!
    cctaylor and gavreid like this.
  4. mansr

    mansr Objectionist

    It retains heat better, though.
  5. Nero

    Nero Call me 'Goose'

    I'm speccing one of these at the moment. Gorgeous things
    dweezil likes this.
  6. Mike Reed

    Mike Reed pfm Member

    Maybe if compared to 2mm or 3mm glass, but I reckon that 4mm toughened might challenge it. I've had many greenhouses, both 6 x 8 and 8 x 12, with either 2 or 3mm horticultural glass. I learnt my lesson and bought the best ally g/house out there; the Rhino (Greenhouses Direct) I followed my 14 x 8 byr a 12 x 6 a few years later; never had a breakage or problem. Y' pays y' money.....

    A 6x 8 is the standard, but you can never have a g/house which is big enough. However, if width restrictions are paramount, see if you can fit a 10 x 6 or even a 12 x 6; little extra cost and therefore exc. v.f.m. (As in my avatar). I could now sell both g/houses for the price I paid within a decade; nice not to suffer depreciation !
  7. hifilover1979

    hifilover1979 Bigger than you...

  8. mansr

    mansr Objectionist

    The air enclosed in the double-walled polycarbonate panes acts as insulation. You don't get that with solid glass.
  9. Mike Reed

    Mike Reed pfm Member

    Understood, and I see from the link above that clear (transparent?) poly can be bought but at nearly £50 per m2, not cheap but good value if you (like the o.p.?) have the g/house frame anyway. No idea how thick this stuff is, but the pane recesses in your average g/house aren't that deep.

    As I've found in this crappy season, warmth alone is not sufficient to produce ripeness, flavour AND sweetness in tomatoes; prob. other crops as well, so anything not transparent is, i.m.o., a poor compromise. Once in, toughened glass, and esp. 4", is almost unbreakable in normal circumstances.
  10. mansr

    mansr Objectionist

    The ones in my mum's greenhouse are 6 mm or so, quite a bit thicker than typical glass. The actual plastic is maybe 0.5 mm. In the 30 years it's stood there, none of the panes have broken, so the material seems to be plenty strong.

    The double-wall panes aren't clear like glass, but they still let a lot of light through, if scattered. Nevertheless, there is likely a trade-off between light transmission and heat retention here. Which material wins probably depends on the local climate as well as what crops are being grown.
    Last edited: Sep 10, 2021
  11. dweezil

    dweezil pfm Member

    This year's really shown the benefit of maximum light, for tomatoes light is yield and sugars.

    If you've got a good site it can get too hot and bright though.
  12. Mike Reed

    Mike Reed pfm Member

    You're probably right, as I've no experience of anything other than glass; sufficient experience, though, to consign horticultural glass to the skip.

    Too hot if insufficient ventilation (unless over 30 degrees outside). Just 'bright' is no substitute for direct sunlight; at least on tom's, capsicum, aubergines and the like. I've now grown my spring onions in the hottest g/house for 3 years and, despite being an 'outside crop', they've been superb; fast growing and unaffected by heat.

    I'm transplanting more now that the tom's have finished. Exp. in supermarkets, so worth growing.
  13. gavreid

    gavreid pfm Member

    I've given up with toms as they almost never ripen before the late blight gets them in my space. I'm sure it's lack of sunshine rather than temperature. I also find chillies usually ripen in November from an early sowing. I have a small, old, glass and aluminium Eden. It's been excellent. Poly is probably fine in an open and sunny site, probably beneficial for a bit of shade, but if not then glass all the way. If there're young kids to be going anywhere near a glass greenhouse then I think toughened glass is the only safe option.
  14. Mike Reed

    Mike Reed pfm Member

    That's odd, as I've never had browned off tom's in any g/house, except for one or two this year in my big one with little sun getting in. Outside, they go brown/rotten very easily with low temp's and cool/cold winds. You should be fine with your Eden as long as the tom's are in the soil and not gro-bags or pots.
  15. zippy

    zippy pfm Member

    Just as an aside, I had one tomato plant left over from those I sowed for greenhouse planting.
    I put the spare one in a tub on the patio and left it to fend for itself.
    The greenhouse toms were treated as per the instructions on the packet, grown as cordon and they turned out fine, but the crop not very good.
    The patio plant has produced about twice the crop per plant of the greenhouse ones.
  16. dweezil

    dweezil pfm Member

    Strange year, my greenhouse plants are dead now, last year they were still going in November.

    I was blaming the cheap grow bags but everyone seems to have a poor crop.

    Outside they were looking great but now blight is coming in, big potato growing area and every crop has had some in for a while.

    We had one blocked sprayer nozzle one day and it's left an infected stripe right across a field.
  17. Mike Reed

    Mike Reed pfm Member

    Terrible way to grow tom's (i.m.o.), but this year is the worst I've experienced for ripening and flavour in tom's. Luckily we've got beans coming out of our ears and courgettes have finally done well.
  18. clivem2

    clivem2 pfm Member

    Does anyone here have experience of having a brick base built for a traditional victorian style greenhouse. We're looking at one that's 2.5m x 3m from Alitex - so it's quite pricey already.

    The brick walls would be 675mm high, 2 bricks deep, foundations - all to an accuracy of +/- 5mm and of course level. It's the accuracy thing that's the killer - most builders don't want to do it. I'm getting prices of £6k upwards (rather more from Alitex). The thing is that if the installers from Alitex come along and say, this isn't to spec would be a very costly error...getting the base built on the cheap is fraught with risk. What experience do other fishes have out there?
  19. dweezil

    dweezil pfm Member

    They must be having a laugh!

    Get exact dimensions from the manufacturer first.

    I did a simple trench foundation about 9" deep; as you say accuracy is crucial so all the pre drilled holes line up but a lot of them will be slotted giving some leeway.

    I did the base then laid out the bottom of the greenhouse, marked up and didn't do a final torqueing of the bolts until the end.

    Use new bricks if possible, i used recycled soft reds which varied, light cement can look better too.

    The greenhouse itself is basic Meccano but read the instructions twice at least.

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