Perimeter greenhouse base re-bar or not?

[aidan.f]

We are installing a 2.4 x 1.8 m greenhouse and have decided on a concrete perimeter base with central path (cast separatly) as the most flexible option. I plan to cast a 450mm width rectangle, finishing / final levelling with precast slabs.
Should I insert re-bar in the base to prevent cracking and if so  how many and in what manner? The green house is glazed with 170kg of toughened glass.

[hairyhippy]

My dad's greenhouse foundation has sunk in one corner over the last 20 years or so. It looks mad because you can see through it and it is all slightly out of square. It drives me crackers. I would over engineer your base, think about it, then over engineer some more and then add a bit more just to be safe.

[HeltorChasca]

Is the glasshouse a Hall's by any chance? I've put a few of these up over the years and have two in my garden the same size as yours. They are great. Greenhouses will transform your growing abilities.

Just to clarify before I answer further: Are you thinking of putting the bars within the footings of the concrete base? That's one way. Normal angle iron will do. Rebar proper is overkill. I assume you will be using normal concrete blocks for the base. Or maybe decorative brickwork? The other way is to slip lengths of angle iron under the aluminium 'skirting' at the bottom of the GH below the panes. These would sit on top of the base and you would fix the lot down. One GH I've done is bolted directly to a concrete pad. Then I cut out 2 trenches either side of the length and with the said 'path' down the middle. Depends if you are using staging or planting direct.

Exciting. My free range chickens use one GH in the winter to warm up and dust bathe if the sun is out in the winter.

EDIT Top tip. Make a large right angle triangle (called a square) as it is imperative the GH isn't sheared when you fix the frame together. You won't know until you put the glass in. And if it does go together without gaps, some of the panes will be under strain and others not. Eventually they'll start to crack and fall out. Prepare yourself for painful thumbs and fingers from all the hundreds of springs that hold the panes of glass.

[rafletcher]

For a 6 x 8 greenhouse I'd just cast a full slab, especially if you'll be using staging. The amount of soil available is small otherwise, and needs replacing often to prevent build-up of disease. And nothing grows well beneath staging.  Even if you want to keep one side clear for tomatoes for instance, you'll still be using pots & trays  / gro-bags / some propagation system.

See here for some info on cast bases.  http://www.littlegreenhouse.com/base/base.shtml

[LittleWheelsandBig]

As a civil engineer, I chuck some welded mesh into just about all domestic concrete slabs to minimise crack width. The amount of reo theoretically needed depends on the thickness.

[Poly Hive]

Having said all of that my previous glass GH was 8 x 12 (I think of might have been 8 x 10) but it sat happily on a concrete pad which was some 3" thick and there were no issues at all with movement or cracking.

PH

[Canardly]

As LWaB says stick some mesh in preferably with 50mm cover. Its cheap enough and will provide peace of mind. Somewhat obviously, do not lay when frosty conditions are likely.

[aidan.f]

Thanks for all the good and comprehensive advice

[Aunt Maud]

You'll need to engineer the foundation and slab so that the foundation and slab don't make the foundation and slab sink due to their self weight. The greenhouse itself doesn't need thinking about IMO.