Poly tunnel - cost effective?

Especially with the rubbish weather we have had over the past 18 months, I am starting to think about the possibility of using a polytunnel as a way of extending my growing year, growing more things that are expensive in the shops - tomatoes, peppers, salad stuff, maybe sweet potatoes, etc and having somewhere I can control the environment a bit and actually do some gardening.

My approach would be to run a four year rotation on my outside beds and divide the polytunnel into a four year rotation as well, but instead of brassica (which don't like it warm) I would put strawberries in their place.

I can afford space for a 10 x 20 foot tunnel. Not sure about prices yet so I may need to pull back a bit there.

My concern is are they cost effective? Do you ever get your money back?  Is a bigger tunnel more cost effective than a smaller cheaper to buy initially? Any suggestons?

I can't answer your question, but have you checked your allotment rules - we're not allowed polytunnels on ours...

ours was fine this week, had 65 mph winds and the thing didnt budge. the plastic cover that goes over the frame is buried about 1ft so that kept it sturdy. we got ours from ebay for around £60 inc postage. has galvanized poles so they dont rust.

we got the 19mm poles and 4.2 mtr long
 they have 25mm poles but cost alot more
http://www.ebay.co.uk/itm/Fully-Galvanised-Steel-Frame-Polytunnel-Greenhouse-Pollytunnel-Poly-Tunnel-New-/380565726830?pt=LH_DefaultDomain_3&var=&hash=item589b7c266e

I also bought one of the eBay tunnels with galvanised frame, though I got the 25mm version, and I've been very pleased with it. Mine has also stood in some very high winds. The frame is very solid but you can't expect the cover to last too long, but even if you replaced it every year it would still be cheap. And if you wanted to, you could always buy standard poly sheet to put on the frame once the cover wore out. Mine is 6m X 3m and I have four raised beds in it so I can rotate a bit. I've had it for 18 months now and I have things growing in there all year round.

Don't feel you can only grow the hot weather stuff though. I experimented with all sorts last year and did well with cabbages, chard, leaf beet, spinach (last year's still cropping), early mangetout (doing early French beans as well this year), early new spuds, carrots, kohlrabi, radish, spring onion, beetroot, swede (did well but won't be doing that again because they were too big), celery, as well as the obvious salad and tender stuff like lettuce, tomatoes, cucumbers, aubergines, peppers, courgette (just did one Parthenon for early/late crops). I like growing the leafy crops in there because the leaves are always perfect, no holes or weather damage. I didn't do so well with melons last year, but it was a pretty bad summer.

I think my old polytunnel has more than paid for itself.

We got it in 2006 from a little nursery that was closing down for £60.  It was 30ft long, but Brian made it 24ft long to fit the space.  It is 20 foot wide.

When I researched, they reckon you shouldn't re-use the polythene if you take it down then re-erect it.  We did re-use the polythene which was already 5 years old, and now its had another 7 years of use.

Needs a new poly now, but as I am hoping we can sell this place soon, it isn't worth the cost.

But thinking about all the lovely tomatoes, peppers, chillies, cucumbers and other things I've grown in it.  Well worth it!

Luv my PT had it 3 years nar its brill
Dunt look at it as whether its cost effective but the enjoyment av had out of it is priceless.

It would be cost effective if you built one from plans and photos readily available on these forums and the wider internet, using reclaimed materials and at worst the cost of a few lengths of timber and some screws. You can build it as robust as you want and design it with a surrounding trench.