In his blog about building his new 6x8 HFGH, dewey1945 shows how he applied 6 mil UV resistant plastic to the outside of his panels. I havenâÂÂt seen this idea discussed anywhere before, so IâÂÂm interested in following his blog: Apply the UV Resistant Skin When I replaced my roof panels in October of 2011, I applied a clear marine coating product to the outside of my new panels, before installing them. I also applied the same product to half of a scrap of HF polycarbonate (left over from installing my exhaust fan.) IâÂÂve left it exposed to the sun since October 2011. So far the treated side still looks shiny and clear, while the untreated side has started to look a bit dull and cloudy. Might be a good sign, but I think itâÂÂs still too early to tell if this product really does help. My cost to purchase a gallon of the product was around $100. The company (Top Secret Coatings) seems to have changed their product line since my purchase, so IâÂÂve emailed them to ask which product is the current equivalent of what I used. IâÂÂll post back here as with that info as soon as they reply. ItâÂÂs too bad we have to wait at least a few years to see if ideas like this truly will help extend the life of the HFGH polycarbonate panels. From my reading, folks in southern states with intense sun seem to report more panel failure. The topic hasnâÂÂt come up here at GardenWeb for a while, so IâÂÂm hoping that means folks in other climates arenâÂÂt having nearly as much of a problem. If you donâÂÂt do anything to protect your panels, and notice some problems in years to come, you can order replacement panels from Harbor Freight. The HF panels wonâÂÂt last as long as higher quality twinwall polycarbonate from other supply companies, (with real UV protection,) but they do cost a lot less. FYI, hereâÂÂs a summary of my pricing research from October 2011, for just enough material to replace the roof on my 10x12 HFGH, including shipping to my state: Farmtek 4mm twinwall polycarbonate, approx 10 yr warranty, about $410 Solexx 3.5 mm, (a flexible translucent white greenhouse covering material) about $350 Harbor Freight 4mm panels, $135 IâÂÂll be sure to post back with the Top Secret clear coating product number, so itâÂÂs recorded here for the thread.

cuestaroble, There are quite a few makers of a material called corrugated plastic which is widely used for reusable packaging, especially in agricultural applications. The most common resins used are polyethylene and polypropylene. They look almost exactly the same, but respond differently to impact and temperature extremes. The primary chemical difference between Solexx and other similar looking materials is the UV additives; however, there are several manufacturing concerns as well. Most plastics will break down rapidly in the sun, including polycarbonate, if not treated. Polycarbonate has a coating on one side that will protect the plastic from the UV damage. Solexx does not use a coating, but had the protective chemicals throughout the resin. Again, you cannot see the difference at all, but it becomes evident after exposure to direct sunlight. Recently we conducted a test with the Solexx material under lights that simulate the sun in Arizona. After the equivalent of 12 years of constant exposure, the Solexx showed NO signs of deterioration. Other corrugated plastic products we tested lasted between 6 and 18 months. This is also consistent to the field results weve seen. Im not an expert on commercial growing, but I have seen quite a few greenhouses and do talk to quite a few growers. Im sure there is someone out there that can give you a more complete answer, but heres what I know based on my experience. Most commercial growers that use the shaded polycarbonate would do so with high value plants or if they are in an area where they have very intense sun exposure and have problems with overheating. Orchids would be an example of a plant that does not like the direct light but does well under bright diffused light. Strawberries are another crop that loves the high light and heat but will burn under a clear covering. The most common place for the shaded polycarbonate on the greenhouse is on the endwalls. In some ways, the covering you use on your hobby greenhouse may be more important than that on a commercial structure. With a large structure its much easier to control the temperature. With a small greenhouse its easy to overheat the structure and overheating is one of the biggest causes of plant death in a greenhouse (this is for hobby greenhouses, so Im not positive it is also true for commercial growers). Also, the light intensity of clear materials will cause excess heat and a small greenhouse will get hot very quickly. Hope that helps. MollyD, Snowload is a bit tricky because it does depend a lot on the structure. We put 1200 pounds of wood pellets on top of an 8ft Solexx greenhouse and it held the weight. We added another 400 pounds and the roof sagged significantly, but it didnt fail. When we removed the weight the structure popped back into place. If the supports are strong enough to hold the load, the Solexx panels will hold the weight between the supports (provided they are placed about 24" apart), but it will not compensate for a weak frame. We have many customer testimonials and pictures of greenhouses that have been completely covered in snow, but its difficult to translate that to a custom structure because we dont know how they were built. There is a chance that your frame would be strong enough to keep and cover with Solexx rather than starting with a new frame. You would need to figure out how to hang lights, but my guess is that you could build some simple framing and add vents and a fan. If you can save the frame and the labor you may have enough money left over to come up with some pretty creative solutions. Do you have a picture of your current structure? mmoore

birdwidow, "It only slopes about 1/2 inch, but for an 8 ft run, that's enough, and not to having to deal with valleys sure made laying the foam, OSD, concrete board and tile a lot easier." What does OSD stand for? I just got the building permit for my 8x16 lean-to GH yesterday, and started removing sod from the location today. So I am very interested in the recommended techniques for preparing the foundation area. My guess is that OSD stands for OutSide Drain, but that's a pure guess. From what I have learned so far in this forum, I plan to excavate at least a foot down, place a little sand, put hardware cloth over that (to stop the varmints), a little more sand, some Landscaping Cloth, some crushed rock, and some pavers on top of that. I'm wondering if I should bury some PVC drainage pipe in with the crushed rock. This is a crude Photoshop simulation of what the GH will look like against the house. A door opens from the lower level into the the GH and a crank-out window also can open into it, which should let the GH be a "parasite" to the furnace room for at least some warmth. Initially the upstairs electric clothes dryer vent also opens into the GH. The dryer has a lint filter, but if lint starts to become a problem, I may do something about that. This is in the backyard and the greenhouse faces south, so it should get about as much sun as is possible in this location. The house will shelter it from north winds. However, our winter days are quite short here in Maine, so I may supplement them with fluorescent lighting. MM

wantabe: the wind speed increases after a short distance down/up wind. I think the reasons for this is the bernoulli effect due to the local space for the air being restricted, and the momentum being transfered down the face of the wall by the coanda effect, perhaps google can tell you? The theory is sound. Solid objects will reduce the wind speed up close, but then the wind will travel faster further downstream. A porous screen on the other hand will have a large area of reduced wind with a gradual return to original speed. Regarding theories being wrong, science does not make incorrect theories so much as theories with low predictive accuracy. The classic bumblebee argument is discredited here: http://www.math.niu.edu/~rusin/known-math/98/bees We replace theories with more predictive ones as we get better. This does not mean the old theories are wrong, and often they are still used when precision is not requried (I use Newtonian mechanics when designing mechanisms rather than Einsteinian mechanics, because at everyday speeds the two have the same predictive power. Rather than building a wind break (which is a tricky art), a simple and effective solution would be to buy a taped shade sail large enough to cover the whole greenhouse and anchor that into the ground over the top to form a flatish tent. There are screw in soil anchors that would be quite adequate for this job, as long as the sail can't flap. http://www.shadesails.com/ready%20made.htm