This may seem a little more costly than you want to do but I like to use baseboards (ground level 2x4" boards)to hold the PVC from twisting. Pipe clanps will then secure the arches and then you can anchor the base by more methods. An angled steel bar attached to the baseboard could have concrete blocks set on it to hold the framework down at intervals and you can also somewhat secure your plastic/row cover by this method if you prefer not to fasten it. The baseboard allows for fastening a cover and even would permit the whole unit to be lifted and moved.

In that situation I believe the Back wall will move east and west or in and out. The diagonal bracing will prevent it from moving north south or as you stated side to side. The diagonal bracing will prevent the corner post on the back wall from moving but the middle of the wall will move in and out You need to stop the flexing at the point where it is secured to the base that is why I don't think you will gain much by running the additional bracing all the way up the corner posts. The post themselves are designed in such a way that they will withstand a strong wind but they flex at the mounting point. Once you have stopped the flex at the base it is pretty solid. Running the aluminum bracing all the way up will cost an additional $200.00 and gain nothing or at best very Little. That money could be better spent on stopping the back wall from flexing. You could install a piece of hardwood into the base secure it to the wall of the base then put screws through the upper lip into the wood. You could use a piece of angle drill two holes a few inches apart and bolt to the wall stud using T bolts then bolt the bottom to the lower lip on the base or attach it to the timbers or whatever you use for a foundation. Lots of ways to attain the same thing but it all must be directed toward stiffening the base at the lip where the wall stud attachés to it.

Yes, I have read of people bolting them down. How do you do that with out harming the panels? It doesn’t harm the soft polycarbonate panels to put a screw through them. You could drill a small pilot hole and insert a screw, or use the self-drilling screws we used. We only used one screw per panel, roughly in the center of the panel. Man the panels are like cardboard and will be amazed if they hold heat... Normal winter temps are in the 30's sometimes cooler. Twinwall polycarbonate is much more efficient at holding in heat than a single layer of glass or fiberglass. Our lowest winter temps are usually in the low teens, in a normal year. You can check out the different heat loss values for different covering materials, at the calculator I link to below. I plan to run a heater and add a 60 gal water barrel. Most people find that trying to use stored water to retain heat through a cold night doesn’t work very well, especially in a small greenhouse where space is already at a minimum. You might search the archives for more opinions on this topic. I use two 1500 watt heaters in my 10 x 12 greenhouse, zone 8. The link below is to a greenhouse heat calculator you can play with, to figure out the amount of heat you’ll need, based on greenhouse covering, size, minimum outdoor temperatures, etc. When you use this calculator, remember the HF twinwall polycarbonate is 4mm thick. greenhouse heat calculator Should I use washers too? Sure, wouldn’t hurt. Washers will help prevent the bolt heads from biting down into the surface of the wood, as you tighten them down. If you haven't done anything like drilling into concrete before, you might want to find a neighbor or buddy who can give you a hand with it. Weather stripping is a good idea,but even with my smaller model that can be pricey. Where as the screws and silicone or caulk might be cheaper? I bought my weatherstripping on eBay from a surplus seller, for a much lower price than our local box stores. It was too wide; I just cut it lengthwise with scissors. So from your blog I can expect there to be gaps for water leaking in and heat escaping. Not quite sure what you mean; I had a few gaps at the tops of the corner posts, as I explain in the blog, and fixed those with clear caulk. I don't have water leaking in. I also post in the blog that I haven’t regretted the time or money for the weatherstripping, since I think it helps prevent heat loss. I can’t measure how much of a difference it makes, truthfully, since I haven’t built a HF greenhouse without using weatherstripping. Not sure exactly on the aluminum tape at the ends? You said to tape it to seal it then you put holes in it for air exchange which I understand. But if you put holes for air exchange then what purpose is the tape doing? I’ve currently switched to using clear duct tape (Lowes) on my panel ends; it seems to last longer in our high heat. The aluminum tape worked fine, but peeled off after about two years of our brutal sun. Here’s a thread that explains more about this: thread discussing sealing polycarbonate panel ends The above thread also has some information about how to order extra Harbor Freight panel clips, if you decide to.

Carol - If the beams are attached to the concrete floor and floor joists above in a way that does not allow the floor above to move up slightly when the bolts are tightened then you would be correct that they may work against you. I would try tightening a couple Grip-Tites then removing the bolts from the closest beam or beams and seeing if the Grip-Tites can then be tightened more, proving that the beams were holding them back. I think you are right, but I probably would remove all the bolts at once, just in case. Just my thought. --Rick