Greetings from the Shetland Islands...

[greenorelse]

Perhaps veggieman could comment on his sheets but I also would suspect that corrugated sheets would have a tendency to buckle at least a little.

Yes, that would be most useful.
I'm a bit concerned as this idea has caught the imagination of several people on this forum and I would hate for them to buy loads of corrugated plastic sheets, only to find they don't bend as they expected.
Judging by the plastic sheets I recently bought it would cost at least €1500 to clad a 30' tunnel, that's a lot of outlay to gamble.

Yes, at some point in reading and thinking about this over the couple of weeks, I unconsciously substituted 'polycarbonate' for 'corrugated'. The first picture looks like corrugated sheets!

If, like me, you're in the so-called 'republic' of Ireland, I've found these people in Dublin and, according to what I can figure out from an e-mail reply from them, the "10mm TwinWall & 16mm TripleWall MarLon S/T Polycarbonate sheets" are bendable. I've given them details of this thread.

Access Plastics were good enough to my e-mail very quickly with some pdfs and it looks like they know their stuff, but nothing in the pdfs hinted at bendability. I'll be speaking to them on the phone soon so I'll let you know of any more details when I can.

This is getting quite exciting! This year's "major project".

[Green Aura]

The trouble with all of this is it's so flipping expensive! We sat down at the other day to work out what we need to buy and using corrugated plastic it came to over £250 and for the 10mm twinwall polycarbonate, well over £300 - and we only have a 10'x15' polytunnel.

That's in addition to all the wood (which we have to buy from the exorbitant local joiner because we can get 15' lengths of wood in the car ), saddle clips to join it to the frame (the least expensive bit) and stuff to seal off edges etc.

All together, we're looking at about £500 and that's without any delivery charges. So, as we haven't got that I'm afraid we're going to have to resort to another skin for the time being - £60!

Maybe next time

[greenorelse]

The trouble with all of this is it's so flipping expensive! We sat down at the other day to work out what we need to buy and using corrugated plastic it came to over £250 and for the 10mm twinwall polycarbonate, well over £300 - and we only have a 10'x15' polytunnel.

That's in addition to all the wood (which we have to buy from the exorbitant local joiner because we can get 15' lengths of wood in the car ), saddle clips to join it to the frame (the least expensive bit) and stuff to seal off edges etc.

All together, we're looking at about £500 and that's without any delivery charges. So, as we haven't got that I'm afraid we're going to have to resort to another skin for the time being - £60!

Maybe next time

Maybe someone with the maths can calculate the total costs of a polythene tunnel and those of a polycarbonate one over, say 20 - or more - years? Do you factor in inconvenience? Extra warmth because the polycarbonate is multi-wall? Hot-spot tape?

Something else that appeals is the fact that it looks easy enough to attach enhancements like irrigation or crop bars as you're talking about only wood and plastic, no metal.

Green Aura. I think (I'll be happy to be corrected on this) the edges overlap rather than having to be sealed. Also, I have loads of nuts and long bolts scavenged from a job dismantling which are looking for a use, so personally I'd save something there.

[Green Aura]

I'm afraid it's a much more simple equation - we don't have £500 we do have £60!

I've not given up on the idea, it'll just have to be shelved for a couple of years until the skin needs replacing again, by which time we will, hopefully have either managed to save up sufficient funds, or managed to buy all the separate bits at more convenient times - sales, secondhand etc.

[greenorelse]

I understand, GA. I'm in the lucky position of having a ground ready for quite a large polytunnel, the money saved up !!!! yippee !!! and the inclination to self-build something reasonably permanent. We got out of debt some time ago and vowed not to borrow again, if at all possible.

We don't have a polytunnel of any description, so can make the choice based on a number of factors. That's why I'm nagging these people!

[greenorelse]

As far as I can figure out, my question, "What happens at the ridge?" may be redundant. I was assuming that sheets of polycarbonate would overlap around the diameter of the tunnel, in addition to along its length.

Probably not so - the polycarbonate in Dublin is available up to 7 metres in length (according to the website - I'll confirm that when I speak to them), enabling a height of just under two and a half metres and a ground width of around 4 metres - using single sheets.

Herself actually wanted a wider tunnel (five metres) but, if I'm building this, it has to be less. I think height and width have to be as above.

I think I'm right there but some things are hard work figuring it out for oneself. Maybe it was obvious to others...

[greenorelse]

A question to which I'm still trying to establish the answer is the diameter of the polypipe.

Am I wrong to ask?

[nortenergy]

A question to which I'm still trying to establish the answer is the diameter of the polypipe.

Sorry greenorelse, I haven't been back here for a few days.

The pipe is a nominal 90mm if you were buying it new. However all the pipe I've been using has been used and a little worn both inside and out therefore I'm not sure of either the inside or outside diameters.

I hope this helps.

[greenorelse]

Thanks for that information nortenergy.

[greenorelse]

A question for nortenergy or anyone else up there in the Shetlands with these tunnels.

Your polycarbonate sheets are bent along their length like this (I hope this shows up) ∩ ensuring there are no 'ridges'.

Could you fix them lengthways to the polypipe, meaning the overlaps would run along the length of the tunnel? Hope that's clear.

I'm just going through all the possibilities in my mind.

[nortenergy]

Hi greenorelse,

I'm afraid I don't quite understand the question. But please note that my design is quite different from that of veggieman's, and there are no overlaps at all with mine.

I'll take some close-up pictures to help me describe this.

[greenorelse]

Hi greenorelse,

I'm afraid I don't quite understand the question. But please note that my design is quite different from that of veggieman's, and there are no overlaps at all with mine.

I'll take some close-up pictures to help me describe this.

I realise it's not a well-asked question. Difficult to describe but I'm thinking of the polycarbonate running length-wise rather than in hoops.

You have no overlaps? How do you butt the sheets up to each other then? I was working on having overlaps...

[Odsox]

I think it might help if you specify exactly what sort of sheets you are talking about, Greeorelse.
Are they twin or triple wall flat sheets or are they corrugated sheets ?

Multi wall flat sheets butt up against each other on every side, corrugated sheets presumably must overlap on each edge.

[greenorelse]

I think it might help if you specify exactly what sort of sheets you are talking about, Greeorelse.
Are they twin or triple wall flat sheets or are they corrugated sheets ?

Multi wall flat sheets butt up against each other on every side, corrugated sheets presumably must overlap on each edge.

It's these:

I'm using flat twin-walled polycarbonate sheets (google "twin-wall polycarbonate") which generally used on the flat do have a cold bending radius which allows them to bent into shape. Being flat and 10mm thick they can be joined to form an air-tight seal. The ends can be made tight with 'natural cure silicone' and the opening fitted with draught proofing.

...and I think I understand now. I think nortenergy is saying that s/he's butted the long edges of the u-shaped sheets up against each other and finished with 'natural cure silicone' to seal the joints - though the wording above is ambiguous. I first took it to mean the the 'ends' meant the ends of the polytunnel, not the edges of the sheets.

Ho hum. These twin-wall sheets are 2.1 metres wide - I was going to overlap them on 2 metre centres, meaning 5 cms either side of the fixing.

[Odsox]

I think you will find that you can get "joiners" for these twin walled sheets, a sort of double channel that the ends slot into, leaving a flat surface. You certainly can for the thicker triple wall sheets that I roofed my conservatory with.
Hope that helps.