Anna, I'm not sure what your intentions are for the "ground heat sink". In other words, I don't know whether you want it to keep the greenhouse from getting too hot in the summer or to keep the greenhouse from getting too cold in the winter. Normally a heat sink is used to keep something from getting too hot. For example, heat sinks are mounted on computer CPUs to keep them from getting too hot. They are intended to carry heat away as quickly as possible. Their analogy in an electrical circuit would be a ground wire, which "shorts" the circuit to the ground voltage through as little resistance as possible. I am in the process of excavating a foundation for a kit lean-to greenhouse that we ordered. Here in Maine the problem is to keep the greenhouse warm enough during the winter without spending a lot of money for fuel or electricity. During the summer we may not even use the greenhouse at all. So, during the winter I definitely don't want my heat to "sink" into the cold ground underneath the greenhouse. Instead of a heat sink, I am going to use a thermal mass of a rather limited amount of sand, gravel, and concrete pavers. That thermal mass will be insulated from the soil underneath by insulating foam, as much as I can afford. The thermal mass could be likened to an electrical capacitor, that stores current when the voltage is higher and releases current when the voltage starts to drop. That's what I want my thermal mass to do, namely warm up significantly during the day and release heat back into the greenhouse during the night as it cools off. Too much thermal mass won't warm up enough during the day. (A really large electrical capacitor can act rather like a short to ground.) Too little thermal mass will cool off too quickly during the night. There is a "happy medium" thermal mass that I am striving for. I intend to use enough insulation to prevent the floor from acting as a heat sink. I'm excavating deep enough to lay down several inches of insulation, and several inches of thermal mass over that. I certainly don't want to try to heat up the planet through the floor of our greenhouse. MM

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.

boxcar, The foam is waterproof, so if you lay it under crushed stone with no place to drain; it won't. However, if you have the patience to fiddle with the crushed stone, grading and packing it firmly to the center or one end and can dig out a drywell, you could lay the foam over it, leaving the top of the drywell open from the foam, then more stone on top, and the water would drain to the drywell. But it would result in a much nicer and easier to keep clean floor, not to mention tracking the stuff, to just overlay the foam with concrete patio blocks or bricks. As long as the crushed stone is well and truly packed, the foam really will support the bricks or blocks, that will lay easily and could be butted tightly to avoid the need to fill between them. You could even broom mortar into any cracks, wet it and when it dried, would have a really solid floor. BTW, just in case you aren't familiar with drywells- They are just holes dug down to below frost line, lined in the old days with mortared brick or stones and now, plastic liners that can be bought for the purpose. Or, you can use a length of fairly wide plastic culvert pipe. You could also use the same heavy plastic channel drain as I did, except that instead of the section with the drain drop leading to a sump pit, it would go directly into a drywell. There are a number of options, but for any drywell, always- the deeper the better, then fill it with large stones to the top of the liner and either set a made for the purpose cap or channel drain drop section over it, or top it off with with 1/2 inch hardward cloth and lay a piece of window screening over that, to prevent anything other than water from seeping into it. I drain my GH with a channel drain that connects to a sump pit, fitted with a sump pump, that empties the pit to a 150 ft. long line, but I fitted out my GH out to serve as a tropical fish hatchery, so often need to dump hundreds of gallons of water at a time, and have a large utility sink out there too, with H & C water, so it's a different GH use and set-up than most. I also laid OSB over the foam, then topped that with 3/4 inch concrete board, but that was because I wanted a glazed quarry tile floor and it requires far more elaborate under pinnings than do patio blocks or bricks. The tile also lines the kneewall, but there too, my needs were different. All you really need for a GH in which you only grow plants, is a means to drain off excess water from the plants and avoid too much dampness that might cause fungus on them as well as the interior walls of the GH, although the ability to hose down a concrete block or brick floor with cold water is a nice extra, for keeping the GH clean and help cool it on hot days. It really all depends on HOW you want to use your GH, and WHEN in relation to your climate, and how much time, effort and money you are willing/able to spend to fit it out for your own maximum use and enjoyment. After all, a garden GH is really only for pleasure, because unless you are feeding an army of kids, for what it costs to build and maintain one, it's cheaper to shop for veggies at Whole Foods and buy started plants at any nursery. So by all means, put a lot of thought and effort into your foundation and if, after you have the GH you need to back off on the fittings until your wallet recoups; do so and in the end, you will have what you really want. We spent an entire season preparing the foundation for my GH and by the time we actually got to erecting it, all we had time for before winter set in was to install the heater, but as anxious as I was to use it, patience paid off. (Of course, we are also a pair of arthritic old poops, so everything takes us longer now.)

Here's one that looks closer:Traditional anchor bolts. Metal brick ties one block row down are used for anchoring brick veneer.