Greetings from the Shetland Islands...

[veggieman]

I am not how the piping is referred to elsewhere.
Up here it is used as part of the salmon cages found in these parts. They are known as salmon feed pipes and I am afraid that I can't provide any more info. Perhaps, I could look up one of the salmon companies and provide you a name and number for you to contact them direct.
I will have a look and see what internal pics I have showing the end wall.

[greenorelse]

Cheers, veggieman. Actually, I'm going to ask more from you. I'm seriously thinking of going down this corrugated route, it looks brilliant - what are the disadvantages? Give me a few pointers and I'll be eternally grateful.

I have a roll (probably 100 metres) of inch-and-a-half polypipe duct that I, ermm, acquired. Is that too narrow? Yours looks a wider diameter - what is it? What did you use for the stakes? Did you treat the edge boards? What do you use for bolts? Do you use washers? Just a few of the questions that are going through my head...sorry.

[greenorelse]

Another question or two, pretty please. What did you do at the ridge?

Also, does using polypipe eliminate the need for hotspot tape?

[veggieman]

Hi there again.

I didn't actually build the polytunnel. I got a local building guy to put it up for me and he based it upon others in the area. I am thus unable to be technical in any way.
There are round wooden fence-posts within the pipes at strategic points and the wooden frame of the tunnel is bolted through to the pipes at these points. There are similar posts at the bottom of each of the pipes and these are cemented into the ground with two bags of postcrete used for each hole. The boards are made up of treated timber, I recall. I can't tell you what types of bolts and washers were used but the bolts were very long and went straight through the pipes and the round fence-posts within them.
Beyond that, I am afraid that I am not a builder in any way and left it to the guy who put it up for me to do whatever was necessary to make it last in our strong winds here in Shetland. I told him to use the best materials and not to scrimp on any timber that would add to the strength of the structure.

[Odsox]

Could you answer one simple question Veggieman that has me a bit perplexed ?
Are the corrugated plastic sheets pre-curved or are they forced into that shape when they are fitted ?

I recently partly roofed a new shed with corrugated plastic and I not sure I could have laid them any other way than flat, certainly not without kinking and distorting them.
The reason for the corrugations is surely to make them rigid lengthwise and to resist bending.

[TheGoodEarth]

That baffled me too!

Also for extra protection against the wind taking the sheets off have you considered awning straps? These are nylon, very sturdy and can be streched over the polytunnel sheets and secured to pegs set in concrete.

[greenorelse]

Also for extra protection against the wind taking the sheets off have you considered awning straps? These are nylon, very sturdy and can be streched over the polytunnel sheets and secured to pegs set in concrete.

Even a few ropes and (circus?) tent pegs would help, I'm sure!

Hi there again.

I didn't actually build the polytunnel. I got a local building guy to put it up for me and he based it upon others in the area. I am thus unable to be technical in any way.
There are round wooden fence-posts within the pipes at strategic points and the wooden frame of the tunnel is bolted through to the pipes at these points. There are similar posts at the bottom of each of the pipes and these are cemented into the ground with two bags of postcrete used for each hole. The boards are made up of treated timber, I recall. I can't tell you what types of bolts and washers were used but the bolts were very long and went straight through the pipes and the round fence-posts within them.
Beyond that, I am afraid that I am not a builder in any way and left it to the guy who put it up for me to do whatever was necessary to make it last in our strong winds here in Shetland. I told him to use the best materials and not to scrimp on any timber that would add to the strength of the structure.

You're very good to take the time to answer, veggieman. Thanks for that - it all helps get a clearer picture of how to go about building. I'm going to go with it. If it doesn't work out, I'll have learned something. My daughter in Hull knows Davie Sandison, Scottish Salmon Producers’ Organisation's general manager and manager of Shetland Aquaculture; I've asked her to e-mail him looking for specs. of the tubing.

One question you might like to try to answer (anyone?) is the one about hotspot tape. This is essential in polytunnels, where the polythene chafes against the metal frame - I think such precautions might be unnecessary in your 'poly' tunnel. Instead, I'm going to look at bulk buying some rubber washers to help buffer against the wind.

Cheers.

[nortenergy]

Hi everyone,

I'm the chap referenced above who designed the polytunnels in Northmavine, Shetland.

The pictures below are each of different versions:

http://www.communitypowerdown.org.uk/pi ... er1305.asp
The polycarbonate we use is twin-walled or double glazed if you like. Notice that although it is very exposed it doesn't need any windbrakes which blocks out light.

http://www.communitypowerdown.org.uk/pi ... er1306.asp
Inside, whilst still under construction. Making use of recycled walkway units.

http://www.communitypowerdown.org.uk/pi ... er1354.asp
In this one the customer wanted it wider and lower. Notice a window at the far end this time.

All these are community-owned tunnels, however I am now making kits available for others too.

I hope this is usefull.

[greenorelse]

Very, very useful nortenergy. Extremely impressive. A common comment about ordinary/cheaper polytunnels is the loss of height by the walls because of the curve. Your design overcomes that to a certain extent with the 'bowing out' of the walls. A half-way house between curved- and straight-sided PTs.

One thing I would have done in put occasional narrow walkways at right-angles to the main path, to get to the back of the beds.

Thanks a million!

[veggieman]

Nortenergy - thank you for coming to the topic and providing info.
As with my polytunnel (I am in Cunningsburgh), you have the path down the middle of the tunnel which is where the tunnel is at its tallest. I was originally toying with the idea of having the path at a dog-leg so that one side of the tunnel's growing space is wider than the other but with the added advantage that I can grow things to the full height of the tunnel such as runner beans. However, when the path was being set up, I forgot about it so the path is straight down the middle in mine as well.

[nortenergy]

Thanks greenorelse and veggieman,

The interior layouts have been left to the end-user so we've seen some very different ideas. Some of these have been terrible and wasted an awful lot of space.

I'm also prototyping a 4m x 3m version which is handier smaller gardens.

veggieman, you'd be very welcome to come and have a look at a few if you like. I'd be particularly interested if you could give the users some advice on growing. Like myself some are just beginning.

To answer a question above, these sheets are UV protected and have a transmittance of about 87% above 400nm. Comparable to glass (i think).

[TheGoodEarth]

Could you answer one simple question Veggieman that has me a bit perplexed ?
Are the corrugated plastic sheets pre-curved or are they forced into that shape when they are fitted ?

I would also love to know this

[nortenergy]

Odsox wrote:
Could you answer one simple question Veggieman that has me a bit perplexed ?
Are the corrugated plastic sheets pre-curved or are they forced into that shape when they are fitted ?

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.

Although good ventilation is required during summer daytime, during winter it's important to retain as much heat as possible.

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.

Hope this helps.

[Odsox]

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.

[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".