Here is what I learned:

Use Schedule 80 PVC - it is heavier, grey (therefore more sun resistant). It can be purchased at most large discount stores, Lowes, Home Depot, etc.

It bends fine. My design used two 10 foot sections joined at the top spline.

I don't know about visqueen, but I used greenhouse film which can be purchased at lots of large GH or garden supply stores. I used regular heavy plastic film (from Lowes) the first season and by fall it was totally rotten. The Greenhouse film (I used Tuflite IV) will last up to 4 years.

I don't know what zone you are in, but it will not hold heat at night and supplementary heat must be used if you use it during very cold weather.

Good luck.

GD

I only used mine beginning in mid-March and placed the seedlings on the bottom shelf and draped a plastic tent over the bench to the ground, placed an electric milk-house type heater on the shelf set it to come on at about 45°. Of course, the minute the sun hits the house the next day, you have to remove the tent. Mine certainly was not automated in anyway. I started the seedlings in the house under lights.

Bob in North Alabama

What I have so far found it good for, here on the margin between zones 7 and 8:

Terrific lettuce and spinach all winter.
Beautiful carnations and nasturtiums, nasturtiums to Christmas and carnations all the way through.
Started and grew beets successfully, are maturing now outside.
Provided a good spot to keep my worm bins warm enough to stay active without going into the house, which I just don't want.
Nice place to sit on a sunny, cold winter day.
Nice place to do garden work when it's raining.

This spring I took down the plastic on the northwest end to mitigate the temperature extremes that are, for me, the main drawback to the cheap and simple design. Temps are still a few degrees higher than outside (2 to 10, depending on whether I open the other end or not.) I have a nursery bed for my tomatoes in there, and will give them extra cover if temps fall very far. I have also started peas and potatoes in beds and will remove the plastic probably in late April or early May. I'm hoping this will get the spring things mature before the temperatures get too hot and give me a good long spring harvest.

Good luck, best,
Martha

On last impression: think BIG and think FUTURE. You just know you're going to grow and you want something to hold up to 50 mph winds. Why not do it right the first time. I use PVC arches with rebar base stakes to provide support for row cover for winter protection of some herbs but then it goes back to the scrap pile. Most PVC structures I've seen use duct tape to secure the perlins to the arches. Is that the type structure you want to show the neighbors.

I'm not sure what I will do during the summer because it will surely get real hot in there and I used construction plastic so I will probably remove the plastic and put new plastic up in the fall. If it works out well I'll probably get greenhouse plastic when I run out of the cheap stuff.

Heating is impossibly expensive if you are in a cold climate; in winter you can only expect the inside to be a few degrees warmer than outside unless you have a real big heater and an air-tight construction.

Bob B

PVC is very bendy when warm, just don't try bending the bows during a blizzard !

It's wise to put in a ridgebeam of 2x4's glued in a "T" shape to give the bows support. I attached my bows with "U" shaped conduit brackets.

"Use Schedule 80 PVC - it is heavier, grey (therefore more sun resistant). It can be purchased at most large discount stores, Lowes, Home Depot, etc."

Unfortunately Sch. 80 is a special order around here. I did the rebar-inside-PVC trick. I'd sure have ordered the Sch. 80 if I'd known I could.

"So is there anywhere where I get about that much plastic sheeting for a lesser price? "

I've canvassed the home centers and never found any good film wide enough. I don't know where that stuff came from the author of the plan used.

I found that I could use our industrial sewing machine to sew 10ft pieces of 6 mil plastic together.

However, you can buy cut yardage of decent four year greenhouse film.

I went to our local greenhouse and asked where they buy their plastic.

They'd just taken down their three year old plastic and put up new, so I said, "Can I buy the old film, please?"

They said "sure... oops. Cut it up for scrap."

So if you could find this kind of deal you'd have good plastic for a year or so.

Ask for testimonials from people who've bought recently. I used the cheap stuff and it has lasted a year with one or two small rips so far.

Or you can buy a "solar pool cover". It's a very good, thick type of film designed to be a good insulator.

A solar pool cover is peppered with trapped air bubbles and I wish I had one.

Ask CactusFreak, I think he uses one. People who do love it.

It costs more but if you want to have anything growing when snow flies, it'll pay for itself in the first year.

One important tip is to build the greenhouse with two foot high wooden sides.

These "kneeboards" give you much more headroom, and they reduce the length of the bows you'll need and, more important, they mean you can use a smaller piece of plastic to cover.

I sure wish I'd known that tip last year.

""And will it be hard to heat a hoophouse if it has big holes in the plastic (like near the ground), or is there a way I can make it near air-tight?"

You can set up the plastic to be rolled up toward the top of the HoopHouse when you don't need heating and roll it back down in the Fall.

That gives you lots better ventilation and prevents overheating. I'd like to figure out how to retrofit my hoophouse to do that.

*********

If you happen to have a hill on your property, there's a great money saver called a "Pit" greenhouse.

You still use the bows and cover with plastic, but you cut into the hill on the South side.

The earth forms the North wall, and insulates your greenhouse from the cold winds. Properly constructed, a Pit greenhouse will never get below freezing in Zone 5.

A clever trick is to dig down enough to put in a walkway in front of the plants. The cold air that creeps in sinks and fills the sunken walkway where the earth warms it to above freezing.

We have two hills that might work, but I'd end up killing trees to do it. :(

Here is a recent image of the inside. I wish I had planned a bigger structure

The two sites are:

My step by step site

The other site

The bunnies won`t like summer temps in the gh so you`ll also need to move them outside in summer.

no shortage of manure :)

Of the three smaller ones, one is a greenhouse, one is used for a cold frame, and the other one is just the frame to hang baskets in without any covering. The first 2 houses have 5 purlins and the basket house has 7.

Now, his prices are a little steep for some of the other things you might need but we've been really pleased w/ the frames. And he will deal with you.

If you need any more info, let me know.

Regards,

Tom