You could do it either way, one piece or three whichever is cheaper. Either way the ends need to be put on flat and the excess trimmed away. That won't be any different with three pieces or one. Allow some excess all the away around all three pieces.

If you order one piece and cut it into three, top and two ends, each of the three pieces needs about a foot excess on each end. So total length needs to be 32ft + twice the height + at least 6ft to allow 1ft excess on each end of three pieces.

My biggest hint would be don't put it on too tight if it's warm when you apply. Poly shrinks and swells more with changes in temperature than you might think. I put mine on too tight last time and it caused issues later on.

What is your fastening system?

This post was edited by fruitnut on Wed, Feb 20, 13 at 11:02

You probably would need a 30' wide film to cover the 18' structure and since that is a common dimention I'd order that in a length that allows you to cover the framework (probably figure 38-40') and then enough for your ends (don't know your setup). I use polycarbonate sheets, windows or just plywood on my ends so you could use anything; if using film I'd put a layer on both inside and outside of the framework.

Getting the film to lay smooth, without overlaps, requires that you keep it pulled squarely and evenly while attaching (one reason why you should give yourself 3 ft. overlap at the ends until the framework is fully covered securely). It works best if you have two or more people to hold the film as it is secured. This process is just one more reason why I like the wire-lock system to secure the film- you can easily undo a section and re-allign it.

All that being said if you plan on roll-up sides I often will replace that roll-up curtain after a few years b/c it is more likely to be worn thru from repeated fastening at the corners. There are ways to remedy those problems but that is a whole new topic for discussion.

How tightly you fasten the film will depend on wether or not you inflate 2 layers. You should allow a slight amount of slack if you do inflate.

I would suggest that you cut seperate sheets for the ends to avoid "Bunching". With wirelock you can easily attach a second wiggle wire into the same channel over the end film after the arches are covered. Some might cover the ends first and then install the main cover, depending on which you think you will be replacing first.

fwiw I use a piece of composite decking board wrapped over the end hoops and screwed on with conduit straps. Wiggle wire channel will then screw to the composite board. The end walls are separate plastic; the top of the end wall also attach to the underside of that composite board.

If you use the plastic poly clamps that snap over your pipe, put a screw in them for extra strength.

Interesting approach Cole. Can you describe a little more? I typically "Tech screw" a wire-lock base to each end arch- by recip. sawing partially thru the base you can bend them in any shape imaginable. But I can't understand the advantage to the composite decking board, how it wraps over the end arch or what purpose it serves? From what I understand you are making the more extensive "V" cuts into the wirelock base to form it below the arch whereas you could just make the end arch your connection point.
I've heard that some greenhouse people will aviod the wirelock system by 1. sandwiching the base if the film between 3 treated slats (2 outer preattached under film, 1 center-over film and screwed fast at 16-20" intervals) or
2. wrapping lower film 2-3 turns around treated strip to get desired tightness and then securing with a screw at regular intervals.

I've tried both of these methods and can't see any advantage over the wire-loc system, especially if you are short on help to attach or reattach.

Thanks for the info! I'll be attaching it with 2x4's and cedar strips. I would like the wire lock system but it is out of my budget. I think I'll do it in different sections then. I was thinking of ordering 1, 34'x36' for the top and 1, 12'x40' for the sides and cut it to 20' long. There are only certain dimensions I can order. Does that sound about the right size? The greenhouse measures 18' wide, 10' tall, 32' long.

Here are two pics. You'll have to copy and paste the links. With the second greenhouse, I skipped the metal altogether and just made the end hoop out of the composite board.

http://i186.photobucket.com/albums/x252/dotheopposite/1109111532_zps2276f8ff.jpg

http://i186.photobucket.com/albums/x252/dotheopposite/1128121412_zps7a486835.jpg

My greenhouse site is in an open field and exposed to high winds, so strength is very important to me. The second pic shows the decking board wrapped over 4x4 posts set in concrete. It's probably overkill, but I like it anyway.

The decking board also allows me to bend the wiggle wire channel without having to put cuts in the back of it. A screw every few inches, starting at one end, will wrap it nicely. It's much easier material to work with, for me at least. Screws don't spin out and I don't have to worry about weakening a metal end hoop with screw holes.

I like wiggle wire for curves, but I'm going to use 2x2 boards for attaching the plastic to the hip boards on the side.

Those sizes sound right. Just make sure you measure or are certain how long it is over the arch. That dimension is longer than it seems.

Also I've trimmed mine too close after instulation. Then didn't have enough to reattach after patching holes.

Those are nice pictures, Cole. I had envisioned something different to provide a means of "Fitting" end polycarbonate panels. Although I haven't used these I just wanted to mention that there is a manufactured aluminum fastening for ends identified in my supply catelog as "End bow wirelock". These are the regular wirelock with an extra "Lip" to insert the top of a panel to secure it and eliminate air leaks. They cost $16 for a 12' section so they aren't cheap.

Those plastic dementions appear OK Quadcab. I'm just a little more concerned about length of your main cover. Leave yourself a little extra to pull on and allow for less than perfect allignment. Trimming is just easier than taking hours to properly allign. That being said, I did install a bubblewrap section on my smallest GH, a 40' long structure, that was exactly 40' long. It was the hardest film installation I ever did b/c it was very difficult to stretch the bubblewrap and with an inner and outer 6 mil film I could only use 1 wiggle wire. I resorted to alternate clamping 3' sections between 2 wood strips with 2 sets of vicegrips, pulling to give just enought coverage to insert the wigglewire. There are easier ways to handle film installation than that.