Yes, It definetly helps. I am currently using this method, without it every thing inside froze with ice all over it. Since I put up the plastic sheeting nothing freezes anymore.Just make sure that the plastic doesn't lay against the windows or the corrugated glazing or it will suck the heat out of the greenhouse. The bigger the air cushion the better the insulation. Even the windows don't freeze over like they did before.The nighttime temps are about 15 degrees warmer than without plastic. That plus a small electric heater and you've got yourself a heated greenhouse. To go one step farther channel the heat to access two small tabletop greenhouses inside and the temps can stay around 78 to 80 degrees all night long even on bitter cold winter nights. I use two cornhole boards turned upside down and let the heat come up through the holes to heat the small greenhouses Perfect for propagating or seed starting, and it works great. My greenhouse is 10'x 16' with 12' height. Plastic drop clothes on walls and ceiling, wooden door insulated sheeting. Space between plastic and walls is about 3 1/2 inches. I have yet to insulate the floor but that is next springs project. I have many small veggies that I have started from seed and all are doing well. Good Luck.

I downloaded the 8x10 manual from the Harbor Freight site, and compared it to my manual for the 10x12. All parts appear identical, except for differences in sizes and parts numbers, so my expectation would be you'd have similar design weaknesses that we've experienced in the 10x12. The manuals say the 10x12 is 123" tall, and the 8x10 is about 87" tall, so I guess the 8x10 is a bit less of a target for winds...but if I was building one, I'd probably do similar modifications like we did for my 10x12 (cautious me!) I can't find any explanation in the 8x10 manual for the white front panels shown on the Harbor Freight link you provided. You might call the HF technical assistance number, 1-800-444-3353 to ask. The 8x10 manual specifies "transparent polycarbonate sheets" just like the manual for my 10x12, same thickness (0.165) so I'm assuming they use the same 4mm twinwall polycarbonate, but knowing Harbor Freight, they may be supplying something else for the front panels...and then just not mentioning it in their website or manual. I'd ask. Did you find this two-part thread about some Harbor Freight owners experiencing early panel deterioriation problems? Since your climate is similar to mine (some days over 100°) I wanted to be sure. I still think a modified HFGH is a good deal, but some of us in hot climates may find our HFGH panels don't last as long as folks in cooler climates. The person who started this thread (Laserfan) is located in Texas. HFGH Polycarb Panels failing! Some folks supplement their panels with bubblewrap for extra insulation during the winter. I didn't caulk my panels because I like to be able to remove them, for replacing with screens, etc. I did use foam weatherstripping around the edge of each panel. That really slowed down the panel installation process, but I find it gives me a very good air seal around the panel edges. I think dropping the interior temps to 30° below outside temps will be a challenge, and I agree your only hope will be some kind of air conditioner or evaporative cooler, as you mentioned, and perhaps a misting system too. (The smaller the greenhouse, the harder it is to keep cool, and I think the extra height of the 10x12 probably helps a bit with my cooling challenge.) Hopefully someone else has some ideas on that point (I grow cacti so I'm not much help in that department.) ;-) Sheri

MissAgnes, I doubt that you will be able to locate specific statistics for snow or wind load for the HFGH (and I am very doubtful that Harbor Freight has this info, or will attempt to estimate it for you.) To be honest, their focus is not on long-term durability; it's on selling as many inexpensive kits as they can. The rest is up to us, as HFGH owners. I honestly have no idea how this might be calculated for the modified greenhouse; I can tell you that we estimate our modified greenhouse has handled wind gusts over 50mph on numerous occasions, and possibly a few 60mph gusts in the last six years, with no damage. However, our greenhouse is sheltered on the north side by our house, and we don't have any monitoring equipment, so this certainly isn't any kind of scientific evaluation. My guess is the wind resistance of the Harbor Freight greenhouse, built out of the kit, with no modifications, is ridiculously low (laughable.) In my opinion, it's almost certain to fail; it's just a matter of how much time before the event happens. There are many old posts here with sad tales of those who have watched their (unmodified) structure being permanently destroyed by wind. Also, many sad reviews on the Harbor Freight website, from folks who didn't know how critical the modifications were. Same story with snow load; I have no idea who would have exact figures, but I can tell you there are posts archived here of roof failures from snow. The weakest portion seems to be the center of the roof studs, so that's the area most folks focus on, when trying to build for snow load. I have gathered some links to older threads here regarding snow modifications, and they are posted in the Comments section of Part One of my blog (scroll down about 2/3 of the way through the comments at the page below, and look for the question posted by snwplwdrvr.) Part One, Building our 10x12 Harbor Freight Greenhouse Hope this helps!

I posted new photos of the greenhouse (3rd box and floor are now complete) http://www.gbdg.net/g2/main.php?g2_itemId=93 as well as the completed garden http://www.gbdg.net/g2/main.php?g2_itemId=16&g2_page=3 There are photos of another HFGH that features fans. I'm quite certain you can rig a fan up there so long as the extention does not conflict with any bracing you installed (such as the 1/2" rigid conduit that I and others used to brace the walls.) The timbers that form the footing of the GH are 2x12 pressure treated fir. I did that a year ago when I started this project, but today I would have used the same rough cedar which I discovered later that summer at a local mill. I used the same PT fir for the outside steps and cedar for the interior steps. The steps make access to the GH a lot more convenient and being in snow country it allowed the base of the GH to be largely above the level of the typical snowfall here. This is our first season growing in the GH but it's mid-July and we just recently pulled out the lettuce and spinach that had gone to seed. A new lettuce crop (seeds)is in the newly built 3rd box - time will tell how that goes. It gets awfully hot in there though. As for weight, someone else might answer that. I strapped the various shelves to the sides and have seen no problem from the weight of the starting trays. However, I plan to replace the shelves (right now we are using the wire closet organizer shelves) with the style that Cactusfreak features in his HFGH photos. I want the additional space they will provide as well as to have them supported by pipes mounted above the raised bed boxes.