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.

Here's an idea I haven't seen executed...I'm thinking of buying a HFGH plus a full set of replacement polycarbonate panels. I'd do the strengthening stuff with the EMT and all. It looks to me (after examining the miniature model at Harbor Freight) like there's plenty of room in the channels for 2 sets of the panels...I'd install one panel, then a spacer of some kind to create a dead air space, then a second panel on top of the spacer, and secure with screws. The idea is to get double the insulation, and of course sacrifice some light transmission. I figure it's probably no worse then a pool cover in terms of light transmission and people on this board seem to be able to live with that level of light in the winter. I'd definitely use something like the Top Secret coating on the outer panels--or I could even buy a more expensive brand of paneling that I know has good UV coating. How does this sound to you people with the HFGH? Would this work? Thanks! This is an amazing board. I haven't posted in a long time, and not on this particular forum before.

The Top Secret company never replied to my email asking for help with their current product list, so I could find out which of their (confusing) products is the same as the one I ordered, years ago...I guess I'll have to call them. To be honest I didn't have a very smooth experience when I ordered from them, so I have hesitated to recommend them highly, although I did get the product eventually.

riverview11, one heads up about the double panel idea. The aluminum roof ridge is formed with grooves to accept one thickness of 4mm twinwall polycarbonate. Two thicknesses will not fit into the groove, so you'd have to somehow re-think or engineer a solution to that problem.

Same thing with the panels in the sliding doors, and the panels in the roof vents. They are designed with grooves that will only accept one thickness. The vertical wall panels do sit on the exterior of the greenhouse, though, so you could use thicker panels there.

You may encounter a problem with the Harbor Freight spring clips, though, as I don't know if they would accommodate two panel thicknesses with a spacer...I tend to think not.

Of course almost anything can be overcome with creative thinking and a little work, I'm just trying to give you a heads up about potential challenges I can see from here.

Mudhouse, I've been reading your AMAZING blog on the HFGH, including the follow up posts. I understand the roof ridge issue of there only being enough room for a 4mm panel, but I hadn't thought of the doors or vents because I haven't seen anything but the miniature model at the store. I'm thinking that between me and my engineer husband we'll come up with something for those situations. Thank you so much for taking so many hours time to share on this subject. I'm really excited about this project, though it won't get built until after we build our new house. It's tempting to just go ahead and buy a 6x8 to use at our current house to figure out these issues! That way I'd have a nice place to overwinter my tropicals. We're also in the desert where it gets above 100 degrees F in the summer and have once in a great while we have 70mph winds.

One reason I'm aware of the door panel issue is because I put aluminum tape over the raw edges of the door panels...(an unnecessary, overzealous, and silly thing to do) ...and discovered that even the thickness of aluminum tape on two edges was enough to make a fit problem; they would not go into the grooves. I had to strip off the tape to install the door panels, good grief. (Have you ever noticed how well you remember a mistake?)

I am sure you will have no problems finding solutions. Our approach was to take our time, have fun, and think about options as we went. There are lots of different approaches to the kit, which is one reason I think it's popular with folks who are willing to use it as a starting point, and take it where they want to go.

Cooling will be a challenge for you as it is for me. The winds here are getting up to around 40mph for four days in a row now...not dangerous but surely annoying and unhealthy for working outside. Bah humbug.

I don't think you'll regret any online reading you do beforehand...it sure was a lifesaver for me. Good luck on your build for both houses (real house and greenhouse!)

I just bought the 10 x 12 kit, and seeing as I have a few weeks before we actually start to build it, I would like some way of trying to treat the panels in the mean time. Was this by chace the product you used mudhouse?

Here is a link that might be useful: Top Secret Silicone Epoxy

verdantvivariums, I just got off the phone with Top Secret, and they looked up my order from years ago. The TS-100 you linked to is the product I ordered. It does not say "TS-100" anywhere on my can, so I wanted to be sure.

Their website confuses me because if you do a product search for "TS-100 gallon," you'll find ten different listings for the one gallon size, all with the same name, same photo. I asked the phone rep about this, and he said he thought they were all the same product, but that it was probably best/easiest for you to call, if you decide to place an order.

In the application directions on the website, it states: "Dilution is required in virtually all applications. Use only recommended thinners." And on my can, it says: "Reduction: Use only TS-101 Thinner. Most applications will require 20%-40% dilution."

So, I also ordered a one quart size of TS-101 thinner, mixed that, and applied two coats. I used a low nap roller. Upon application, I could see a very slight yellowish cast, but it was barely discernible.

In a few months it will be two years since we replaced our roof panels, and I coated the new roof panels with this product before application (on the outside surface.)

I just took a quick look at my roof panels (lifting up my Aluminet shade cloth) and I still don't see any indication of pinholes developing, cloudiness, or obvious yellowing. So, fingers crossed that this product may be slowing down the deterioration that I experienced with my first set of Harbor Freight roof panels (those lasted under 4 years, and were in terrible shape when we removed them.)

I still have to stop short of saying that I'm positive this product makes a difference...because of the time frame...but, it certainly does not seem to have caused any problems with my roof panels. I will be replacing most of my wall panels before winter, and I plan to coat them with the same product (I have plenty left over from my original one gallon purchase.)

Thanks so much for following up on this, I should have done so earlier in this thread, as promised!

mudhouse. If you make sure to purchase polycarbonate sheets that are UV protected then you wont have to paint them with goo!. Mine has lasted for 8 years without any major issues. The polycarbonate sheets at the hardware stores isn't always UV protected. I ordered mine online and it had a blue mask on one side indicating which side faces the sky. I went to one of the local home depots once looking for some smaller panels to use as cold frames. But the only polycarbonate sheets I could find locally was single wall and corrugated panels neither of which was UV protected, definitely not suitable for use in the sun or as a greenhouse in cold climates.

Here is a link that might be useful: Polycarbonate Sheets and Greenhouse Panels

Thanks chrisreese, you're correct that good quality polycarbonate comes with one UV protected side, and I think most come with something like a 10 year warranty. And you're right also, in my experience these have to be ordered online, as most folks don't have a local source.

Unfortunately, the twinwall polycarbonate panels that ship with the Harbor Freight greenhouse kits are of poor quality when it comes to UV protection (that's my own experience, anyway.) Harbor Freight greenhouse owners were not aware of this problem until the kits had been out in the marketplace for enough years for the problems to begin to surface.

Now the topic is discussed on the internet, so new owners of these greenhouse kits are understandably looking for ways to improve the lifespan of the panels that come with the kit, and that's why the above clear protective coating product is being discussed.

When the Harbor Freight panels need replacement, we HF greenhouse owners have a choice; order more HF panels (which are already presized for a perfect fit) or purchase good quality UV protected polycarbonate from a greenhouse supply company, and cut them to fit the many different shaped openings in the aluminum framework. Not difficult but it definitely takes a bit of time.

As I posted above, my own pricing research showed that the Harbor Freight panels (which only last 3-4 years for me, uncoated) are about one-fourth the cost of the best price I could find for the "real deal" UV protected polycarbonate, when I included shipping to my location.

If we can find a product that can be rolled on the HF panels, that actually increases the UV protection, it could be even more cost efficient.

So, it's a question of price, and how often folks are willing to do the work of replacing panels.