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

Hi, I have more of a question than a comment. I live in Inverness FL and it gets into the 40's here sometimes. How can I keep my garden warm in the winter but not have it cook in the summer? Right now I have PVC hoops set up for shade cloth. If I put plastic over the hoops for the cold weather and just rolled up the sides and put shade cloth on the top in the summer would that work? Also, what would I have to do to actually be able to grow all year long? Thanks, Maria

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.

Horizontal cracks like the one you describe are definitely a sign of bowing walls. This problem can be caused by a combination of poor foundation drainage and soil composition. Clay soils are known to cause this problem because they expand when wet and shrink when dry. The good news is that there are technologies out there that can improve drainage without having to dig out the foundation and install new french drains. There are also many options to stabilize bowing walls or return them to their original position, ranging from wall anchors, helical anchors, I-Beams, wall braces, carbon-reinforced strips, etc... all of which are less disruptive and more affordable than rebuilding a foundation. Here's an idea. Many reputable foundation repair companies offer free inspections and written estimates, and if they are have been in business for a while, they also have some experience inspecting foundations for real estate transaction purposes. I suggest you call a few of them, have at least one perform a professional inspection and give you a written estimate. With that written estimate you can then decide what you want to do. Walk away, negotiate down or ask the owner to fix. Consider that the house will have to be fixed at some point. I believe the current owner will have to do it if he wants to sell the house. Banks usually frown upon issuing loans to buy properties that have serious structural issues -- even if you are willing to buy it "as is" with a substantial discount. But since you really like the house, it is a good idea to get an expert opinion, know exactly how serious the problem is and how much it will cost to fix it, since it won't cost you nothing to find out. Hope this helps.