here is a post I put up elsewhere, but thought it might be interesting and can certainly save alot of cash as well as give you a flexible space, which is something that a fixed tunnel can sometimes fail to be.
Here are the sketches of our sliding polytunnel contraptions, they are cheap and effective and are more flexible than static systems for season extension (or just keeping out of the rain! ) We use removable end panels with a door overwinter.
Any technical queries or suggested improvements please let me know, cheers!
Sorry about quality of pics but they are scans as I dont know how to stick my Archicad files on here
This is something you build not buy. Its a cheap alternative to many professional set ups and can be constructed very easily. To save sending tons of seperate messages I will lay it out as simply as possible. It can be done by two people in a day quite easily, with some basic tools and a bit of sweat.
1. Set out the rails by putting in a string line and banging in some short stakes, we used treated 2x2, about 2' long at some 4' spacing. You can form rails either twice or three times the length of your tunnel, depending on how many beds you intend to use under the tunnel. The rails are set out parallel and spaced apart the width you want you tunnel to be.
2. Fix the rails themselves to the inside of the line of stakes with some large 4" screws. We used a section of 9x2 with a 3x2 fixed to the inside bottom edge of this, this creates a ledge which the tunnel runners slide on. ( a good bit of candle wax works wonders on this and makes sliding even a big tunnel really smooth!)
3.The tunnel is then constructed out of 1" or 1 1/2" blue alkathene water pipe. This is very cheap and comes in 50m rolls. Simply cut a suitiable length that will give you a curve of sufficient height and width for what you want and then cut as many of these as you require to form a tunnel of the right length when spaced at 6' apart.
4. Each end of these pipes is then inserted into a 4" deep hole drilled into the top of a 6x3 treated plank. These planks are slotted onto the ledge in your rails, and the pressure created by the bent sections holds everything tight against the outer rail.
5. Now you have your basic hoops you add some more pipes lengthways inside the curves to hold all the hoops together. (some diagonals at each end help if its a big tunnel) These pipes can be clamped in place with pipe clamp fittings from a plumbing supplier which are tightened around the hoop section and then the long pipe crossing it.
6. Then you cover the entire structure in your polythene sheet. This is best done from one side, where you fix a 2x1 batten to the runner along the bottom to clamp the plastic in place. Then pull the cover over tight and use another batten to clamp the other side. Then tuck the ends inside pulling them tight and securing with polytunnel sticky repair tape.
7. There you have your basic tunnel which can be used to start early crops in one position then moved to expose them once underway and then it forms a summer cover for tender crops before moving on again to extend your season by covering some late salads etc. We find this stops the tunnel space being takebn up by crops that would be fine outside once established. The possible combinations are endless especially combined with cold frames as well!
8. You can then add removable end panels with a door flap, made of more curved alkathene but with a piece as a base rail (the corners connect with pushfit plumbing joints) covered in polythene.
9. We put end caps on our three longways pipes and connected them to the hose so that they are full of water under pressure and have little sprinkler head (the little ones that you pull 'on' and push back in to turn 'off') every 2' so that there is no seperate watering equipment as it is part of the frame itself.
Hope this helps, happy growing all year round !!!!