Polytunnel design 'restrictions', any ideas?

Hi all - long time gardener, new to the forum, and about to design and build my polytunnel.

I have some old lengths of underground water pipe , a bit thick polythene sheet and lots of lengths of spare wood.

I plan to build it over a raised bed that I did last year and has done really well this summer - it's about 1.5m wide by 3.5 long.

If it was just building a polytunnel, then for me it wouldn't be a big challenge as I am very a DIY person .

However , I have a very specific design issue that has stumped me and I need some input from more experienced polytunnel folk, if you would be kind enough...?

The problem is that the back edge of the raised bed/polytunnel is (would be) right up against a fence that is a boundary and can't be moved. this would restrict the hingeing backwards when you try to to open it.

I have thought of just making it hinge at the ends but again, there is no room for the 'roof' to raise into.
And if I made a tunnel with no hinges but just lifted it off every time I wanted to access it, then not only would it be very heavy, but I have a small space and it would be bigger than any 'empty' part of my garden - ie it wouldn't be practical.

So, bearing in mind I cant move the location, I cant move the fence, but have the materials - what creative, innovative ways could you suggest to get something working for me?

Thanks in advance
Che

 

So lets see if I've got this right, you want to hinge it so it lifts like a cold frame lid, rather than have a door at one end? Is that correct? If so, can't it hinge forward or would that restrict access?
You could rig up a sliding door to one end depending on available height....or better still, an up and over side like a bread bin(that would be cool!)

 

Could you give us dimensions, Che? That would help give us a clearer idea of what's do-able...

 

Yes, you summed it up correctly. There is no access to the rear side of it, as a fence is right up against the back of the raised bed it would be built on (so not only no access but a 'pivot' of a top section would just bump up against fence and stop rotation . - likewise on either end (fence one end , big Camellia bush the other.)

The 'bread bin' concept is not something I had even vaguely thought of, and might be the solution . I just need to work out the mechanism for that option. My next thought is , 'would i be able to create a 'joint' along the length of it when closed that is sufficiently tight to not let all the heat escape?

Many thanks for your input, I will get back to sketch pad and see whether I can get anything. I'll let you know how it goes if I go that direction. Regards

 

Ok, so it is 3.8m long, and 1m front to back . These dimensions are NOT flexible and the rear edge is literally within a cm or 2 or fence.

 

Could you put the frame up and polythene on the ends, then you could roll the the main cover over.
You don't say how high you want the structure.
If around a meter high; you could make a frame along one edge hinged on the opposite long side, fasten the polythene cover along the long side with the hinge pivot, attach the other side to the moving part of the frame and than you can use this frame to open and close the tunnel.
A bit like an car soft top or a 1960's pram hood.
To me it sounds more like a long low cloche than a polytunnel.
Another idea could be to break it down into three manageable sections, two ends and a middle that you could lift off as you wanted access.

 

Nigel, thinking about it you could be right about the name of this structure, maybe more low cloche? Sorry if that caused confusion.

The height will be approx 75cm.

I did think about 3 sections, it's hard to describe how little room for manoeuvring I have on my garden, every space is utilised and this bed is squeezed in and my shed is in this area too.

I will no doubt have to compromise - and the 3 section option compromises on ease of use and easy access. But it's an option

"If around a meter high; you could make a frame along one edge hinged on the opposite long side, fasten the polythene cover along the long side with the hinge pivot, attach the other side to the moving part of the frame and than you can use this frame to open and close the tunnel.
A bit like an car soft top or a 1960's pram hood."

I am struggling picturing that....is that on the same lines as the 'bread bin' concept?

 

Don't take that seriously, I can be inappropriately pedantic.

Similar, but just the polythene moves.
I'd draw a picture except I'm very bad at artistic things.

 

I am aware that I have a habit of referring to things in my tiny garden in a slightly grander scale vocabulary than they might have in the real world . Haha No worries

So the long edge that faces me would be weighted down with a length of wood , but how would the ends of that secure and the polythene tighten up on the ends?

 

Here's a sketch , where the front polythene has been rolled back to the top of the frame for access, and I can visualise rolling polythene around the piece of wood- but once it is taken back down again, the two ends will not close sufficiently and will be exposed to issues with the wind grabbing it

 

Could you make separate semi circular ends and use the sticky back velcro to attach them?

 

I could but that wouldn't give enough access on its own without the front long edge being removable or 'fold-backable'. (in fact one of the short ends of this rectangle isn't accessable full stop and the other is hampered by decent sized Camellia bush)
So in some ways that doesn't solve the (easy?) access problem.

I think I need to work on the roll/fold back of the front long section idea above , and resolve how to secure it when it is down and in place

 

I'd entertain any thoughts/concepts/tips on this, at the moment I am leaning toward a 'roll back ' front , but need to find a solution for how to retain heat and stop the wind catching any lose parts

EDIT - I am now thinking velcro the ends of the long edge to the hoops of the edges of the semi-circle ends? Would that give enough security against wind you think?

 

Hi I've used stick on velcro on plastic before but I found it started getting dirty and lifting off. I was going to make a cover of thick (soft) plastic for something, I have bought polypropylene thread and tape (UV stable) to sew the velcro in place instead. Is there a way you can make a wide channel eg cut a slot in the edge pipe so that the plastic edge runs inside it?

 

I have something similar in this garden - tho without the fence problem. Raised beds 3mts. long, 0.5 mts high and i mt wide.
I bought a clear micromesh cover along with a tubular frame ( 3 mt long x 1 mt high x 1 mt wide ) with zipped opening along one side to give access. You can also get other covers - polythene or green netting.
It works well for me - the only thing I would have liked would have been openings on both sides to avoid the need to bend when planting/picking etc. but obviously that won't come into your set up as your fence stops access on one side.
Being on a raised bed, I'd describe it as a cloche as opposed to a Polytunnel.
Good luck with finding a solution which works for you