I would not be too concerned with any specific brand as long as it is a UV resistant (Greenhouse) plastic and 6 mil thickness. Those special "light dispensing" and "condensation prevention" types are not worth the extra cost in my opinion.

For a 12'(even though 8' peak) I would figure (1/2 Pi * diameter)or 6*3.14=18.84' to get bare min. width so a 20' wide sheet should be good for you. It's doubtful you will find a 16+2=18 foot long piece unless you find a garden center that will cut it for you. If you need to purchase a 40-50' roll I found that using two layers of plastic not only cuts your heat bill considerably but the plastic will last much longer than the 3-4 years they say. I have mine on one 11 years now.

If you have neighbors tree branches to contend with you may as well purchase a roll of greenhouse plastic repair tape. There isn't much you can do to stop a larger tree branch. I would shutter when my kids would hit a "Home Run" ball into the side of our GH but they always bounced off. Be more careful in the winter if you need to remove snow building up around the GH. I poked a shovel thru one of mine each of the last two years.

There are different styles of greenhouse.

Us 'DoItYourSelfers' generally build hoophouses.

If this is the style you're using, get a piece of string, some masking tape, and run it over the bows, taping off every couple of inches, to get the true bow length. Mark this length on the string.

Then pull the string off and measure with a ruler.

For example, I used two 10 ft PVC pipes plus an extra piece between them to get 22 feet of bow length and needed 24 inch plastic.

Be sure to order a bit wider than you think you'll need. Pull the plastic over the hoops, gather it into folds on the ends, pull tight and anchor.

Then just leave that extra plastic lying on the ground on the sides of the hoophouse and cover it with rocks and dirt.

This suppresses weeds.

Are you clear on how to attach the plastic? There's the batten tape way, and the better way that uses spring clips and an aluminum trim piece.

I used batten tape, so I don't even know what the spring clip system costs.

It sure sounds easier though. Find out and fill me in, 'kay?

Hello,

please, can you help me, too?

We are juste covering our tunnel with the plastic. All clips are fixed. Now the plastic-cover has to bee fixed on the bottom of the rail. How we have to do it without cutting the plastic all the long?

Lucy, what do you mean by " all clips are fixed"?

There are a few ways, as JKIRK mentioned to fasten the plastic to the base if the arches(hoops). Almost all involve a 2" treated board that is at ground level and clamped to each arch. I've used all widths- 2x4", 2x8" and 2x10".The width choice is more a factor of how your terrain runs and wether or not you have roll-up sides and how you secure the plastic to the base.

For my first greenhouse I used 3 firring strips to secure the plastic. Secure two strips leaving a middle space to easily slide the third strip between the outer two. After the plastic is put on you can either wrap the base one or two times onto the middle strip before screwing it between the other two or just press the middle strip from the outside, pushing the plastic under it; "Over,Under,Over".

But the wirelock systems are well worth the cost. They range from under $1 per linear foot to $2 per foot if you just get short sections. The base screws fast onto your baseboard and then you just hold the plastic in place with the wiggle wire section. I repeatedly removed and reinstalled end pieces (to keep the structures tight at night after opening in daytime) of the wiggle wire daily during this spring it is almost as quick as zippering a coat. The other benefits are that you can secure another sheet of plastic in the same channel(2 wiggle wires), the channel takes very little width space on the baseboarrd and they last forever.

Hello, bmoser!

I am coming a little late because I had first to translate your message.

Thank you very much for your quite clever system of attachement!

Here my explanations:

"all clips are fixed" would mean, that the plastic-sheet has been put on and attached with metallic clips on the front-arches.
Then we had to secure the plastic on the ground level before "burying" the ends into the trench. And this securing was the main factor of the problem. I admire your system although when it is not the same as the mine,(I need not wiggle wire section), but the your's is very, very clever and handsome-like!
We have metallic strips in the same dimension as you have your firring strip, but in the forme of an "U", and the point of difficulty was, at what side the plastic has to be come. It was right when putting it at the métallic-side, whereon has to be attached a plastic rail together with a middle plastic-strip.This system is able to support the whole side of the plastic-cover-sheet. I am wondering if you understand my bad description. But just this to say that it was wrong - and like this we did in the first time! - to slide the plastic-sheet between the plastic rail and the middle strip. That was cutting the plastic just like a cutter does! Fortunately we could repair this error with a special scotch-sheet for plastic-tunnels and correct our strong mistake.

Thank you once more for your helpful reply. And I like to learn more from other unknown system for us!

Gratefully,

lucy

It seems like you are using an attachment system that involves a securing strip sliding in a groove over the plastic to secure it. I've never seen such a system for greenhouses. It reminds me of the manner by which many screens are secured in the frames for screen windows and doors.

I use another attachment system in one greenhouse usually called a Channel Lock. It has a deep "U" channel and rigid 4' aluminum "U" bars( actually shaped more like "G") that are inserted over the plastic and into the "U" groove by downward and inward motion. They can be used more often without damaging the plastic but they are difficult to attach in cold weather or when there is tension on the plastic. Posibly you are referring to that system?

One important consideration when installing plastic film onto a structure is the outside temperature. The mid 60-70F seems ideal for most situations. Too cool and it is hard to get a snug fit and you may later have depressions where water will lay. Too hot and you'll overstretch the film and shorten its lifespan. I find that attaching a rollup side first or rolling the cut edge onto a section of firring strip allows one person to uniformly pull the film taunt while another attaches it either at the rollup point or at the base.

Yes, you saw right, that's the system. But when you don't have experience with it and you'll do it the first (and even the second!) time, then ist's always difficult. Therefore I think that YOUR system is very clever, because the roll-up mannors gives a better stretching than only with your hands! I will remembrer this idea!
Our temperature has been ok, not cold, sun, and not too hot. Here they say that it must be very sunny to stretch the film but your advice that it has not to be too hot is very important. We would not thinking enough at this point because they say, you have to stretch and to stretch the plastic!

Now, bmoser, I am very curious to hear how you attache the cover on the fronts with rope. We had to cut the plastic in front (of the fronts) of the base structure and to pull extremely this rope. With this power the hole enlarge more than I want, same for the hole cutted in the plastic on the front to attach the rope on the base metallic structure. Do you have another fashion to do?

By "Front" do you refer to the ends of the greenhouse? I don't attach with a rope other than if you are talking about applying the plastic.

In the installation to keep from tearing the plastic double it over and then form it around a round stone of baseball size every 8-12 feet. Throw the loose end over your arches and pull gently and evenly from all of the ropes. The stones or baseballs should keep the plastic from tearing as it is pulled over the structure. Then untie the rope to finish the installation.

At the ends I also use the wirelock on the end arches, By cutting a notch every foot or so you can bend the wirelock base to conform to the arch and use tech screws (drillscrews) to attach. Then you can pull the plastic snug to each end and wiggle wire it secure. I trim the plastic to leave 6-8" beyound the end arch, fold it down to the end and staple it with batten tape to the end panels. You may just want to trim the ends shorter after you are certain that no adjustments are needed.

The wire lock can even be notched and bent sideways to form it along the top of yor endwall paneling. There is a tool to do that but a 18 volt reciprocating saw with a metal blade does the "v" notching very nicely too.