How we survived the Harbor Freight assembly manual, and modified our greenhouse to withstand New Mexico winds (so far)...

Thursday, August 16, 2007

Part Six: Adding the Panels

(A little nagging reminder...)Before you put the panels into the frame, it's really best (in my opinion) to modify the frame for strength (see previous section of this blog.) It's tempting to plan to make the modifications for strength later, but I know several people who had damage to their structure before they got around to adding the additional bracing. Once the panels are in, the wind resistance begins, and you're at risk. My advice is to strengthen the frame BEFORE you add the panels. (It's a lot cooler working on an open frame anyway...once the panels go up, so does the interior temperature!)

On we go. The panels are 2 ply 4mm polycarbonate (about .165 inches thick.)

I sealed the ends of each panel with aluminum tape to help keep dirt, condensation, and bugs out of the channels. I bought one roll of 1 ½” wide aluminum tape (not duct tape) at Lowes, and cut it into thirds, so I only have a small taped rim visible on the panels. You can also buy polycarbonate tape from greenhouse supply sites.

The panels have clear plastic on both sides that you remove before installation. If you remove the plastic you also remove the part number stickers, so I just peeled back the plastic several inches to tape the edges. Taping the panel edges isn’t hard but it’s a fairly tedious process. I brought mine indoors and worked on them in the evenings, laid out on the dining room table. The top edge of each panel is completely sealed, as shown in the photo above.

On the bottom edge, it’s apparently good to have small holes in the tape to allow moisture to escape. You can buy special breathable tape from greenhouse supply websites for this purpose, but others have mentioned using a large pin to poke holes in the tape in each chamber on the bottom edge of each panel. (The holes need to be large enough to allow drainage.)

I used a tool designed to mark leather for stitching. When I ran this tool along the bottom edge it did a nice job of perforating the tape for me, and it was fast. I think a tracing wheel with teeth (used for marking fabric for sewing) might work in the same manner.

Tip: Don’t tape the edges of the door panels (Part 64.) All the other panels are fine to tape, including the panels for the roof vent windows, if you want to. The eight door panels fit into tracks with a tight tolerance (especially if the poly panels have any kind of a burr on the cut edge.) The edges of these panels aren't exposed to the elements anyway, and if you tape them, they can be hard to fit into the tracks. I taped my door panels before I knew how the doors were constructed, and it was quite a battle to get them to fit into the door frame.

Another BIG Tip: Store your panels in a cool place while they're waiting for installation. If you store the panels in the sun, the plastic protective covering can actually fuse to the polycarbonate surface, and it's very hard to remove. I stored my panels in the house while we built the frame, but it was about 98° when we started installing them. I found that even a half hour in direct hot sun made the plastic harder to peel off the polycarbonate, so be careful!

Modifying the Panel Attachment

If your greenhouse is exposed to wind, a major problem with this kit is that the panels are only held in place with these small spring glazing clips.

In a big wind, even if you’ve modified the aluminum frame to prevent flexing (you DID read that stuff in the previous section about frame modifications for strength, right?) these clips aren’t enough to prevent the polycarbonate panels from flexing in their openings in the frame. When the panels flex, wind gets inside the structure and blows the panels out (or worse.)
As a first step, many people recommend ordering extra clips. We ordered extra clips from Harbor Freight, by calling the 800 number on our manual (1-800-444-3353.) They seem to keep these in stock in the Harbor Freight warehouses, so in my experience they ship pretty quickly. (But it never hurts to order early.) We ordered one bag of 130 extra clips, and I used all of them, in addition to those that shipped with my kit.

As of March 2013: If you are ordering extra clips for the Harbor Freight 10x12, the part number for the clip  is 53, and the SKU number for a bag of 130 clips is 29457, price $15.99.

If you are ordering extra clips for the smaller Harbor Freight 6x8 greenhouse, the part number for the clip is 46, and the SKU number for a bag of 72 clips is 27339, price $9.99.

Super Important Modification Alert! Extra clips are good, but this step is even more important: screw the panels to the aluminum frame.

So far, I haven’t read about any panels being lost to winds after being secured with screws. In my humble opinion, I would not attempt to build this greenhouse without attaching the polycarbonate panels with glazing clips and screws. I'm convinced this is important!
Some people put one screw in the center of any brace crossing the panel, and some put one screw in the top and bottom of each panel. Some do both.
We put one screw in the center of any brace crossing a panel. We tried to put screws in the top and bottom of the panels as well, but installing screws in those spots balled up the foam weather stripping I installed under the panels. (More about weather stripping below.) I'll probably decide to add screws to the top and bottom later, and I’ll need to cut out the weather stripping in the area where the screw needs to go.

What Type Screws?
People have used many types with success.
Self-tapping screws with integral neoprene washers, lath screws, or hex-head screws with aluminum washers all seem to work fine. We used No. 8 self-drilling hex head screws, and we installed a No. 8 neoprene washer with each screw.

This is how the screw and washer look on the outside of the greenhouse.
What Length Screws?
Most folks use screws from 1/2" to 3/4" long.
We used ¾” screws, but they tend to go through both layers of the hollow brace, leaving a sharp tip exposed on the inside of the greenhouse. I didn’t like that.
We also found that screwing the panels to the braces resulted in a slight bowing-in of the panel. This is mainly a cosmetic issue; I just thought the panels looked better when they were flat, before we screwed them tight to the braces.

To solve this, my husband used two of our neoprene washers, back-to-back, as a spacer between the polycarbonate panel and the aluminum brace inside the greenhouse. This spacer allowed the panel to remain flat, and it also made ¾” screws the perfect length. They secured the panel to the brace without poking through.
Here’s a close up of the spacer made from two neoprene washers, but a nut or other washers would work just as well.

On the outside of the greenhouse, my husband started the screw through the polycarbonate. On the inside of the greenhouse, I threaded the "spacer" on to the screw threads before it was screwed into the brace.

Here's a photo of the interior wall, using the spacers to keep the panels from being pulled tight to the braces. Red arrows indicate the spacers.

For the panels on the side walls of the greenhouse, I used ten glazing clips for each panel (five on each side) and two screws (one in the center of each brace.)

On each of the roof panels, I used ten glazing clips (five on each side) and one screw (in the center of the brace.)

Generally, I always used more clips for each panel than the manual directed (even on the small gable peak panels.) The kit comes with 260 clips, and I ordered 130 extra. By aiming for a total of ten clips on each of the side wall and roof panels, and adding a few extras to each smaller panel, I ended up with a couple left over. (I may actually order more to be able to add them as needed, if I see any places where the panels tend to move in winds.) The clips aren't hard to reposition, and you can fine tune them as you need to.

Don't forget to put the clips on the door panels too (I almost did.) I used one on each side of the door panel as per the manual.

Caulk or Weather Strip?

Some people also caulk the panels in place. This does seem to attach them securely and also closes down air gaps. I didn’t caulk because I’m hoping to replace some of the polycarbonate panels with fabricated screen panels in the summer, so I wanted mine to be removable. However, I did end up using silicone caulk to fill gaps in various places on the aluminum frame, especially at the top of all four corner posts.

Weather Stripping

Instead of caulk, I used 3/16” thick closed cell foam weather stripping in each panel opening. Closed cell foam is waterproof so rain can’t soak in; look for "waterproof", "weatherproof", or "closed cell" on the package.

The biggest air gap is at the top and bottom of each poly panel; the panel touches the aluminum frame on the sides, but not on the top and bottom. One approach would be to only weatherstrip the top and bottom of each panel. I was worried about heating costs for the winter, so I decided to use weatherstripping along all four sides of each panel. This does provide a nice seal all the way around the panel, but it also dramatically increases the amount of material needed.

I calculated the 10 x 12 greenhouse needed at least 560 feet of weather stripping. (That’s about 32 packages of 17’ weather stripping, each over $3 at Lowes.) I found some packages of ¾” wide weather stripping on eBay for about 1/3 that price. I used that, cutting each strip in half with scissors, so it was 3/8” wide. It worked fine, and turned out to be a soft gray color that was hardly visible under the panels after installation.

People either apply the weather stripping to the polycarbonate panels or to the aluminum greenhouse frame. I didn't know how long the weatherstripping would last in our heat, and I thought it might be easier to remove and replace it on the aluminum frame than on the poly panels, so I put it on the greenhouse frame instead of on the panels themselves.

This frame wasn’t really designed for weather stripping, and the panel openings don’t always have nice flat places to easily stick the foam tape. Sometimes I had to sort of balance the stripping on the high part of a ridge. I found the tape adhered very well, however, and once it was under the pressure of the panel, it formed a very good seal.

If you put weatherstripping on all four sides, you will find you need to use two thicknesses of weatherstripping on the tops and bottoms of the panels (where the gap is larger to start with.)

I used two layers of 3/16" thick insulation, or one piece 1/2" thick, at the tops and bottoms of the wall panels, and at the bottom of the roof panels, as shown in the photo to the right.

We found it was better not to apply weather stripping to the frame at the top of the roof panels, at the roof peak. The roof panels fit into a groove at the peak, and having weather stripping in place made it too difficult to slide the panel in.

Instead, I later tucked ½” foam backer rod into the spaces at the peak. This closes the air gap and presses the panel up tight against the frame. It was just the right size to tuck firmly in place.

Overall, I’m glad I weather-stripped the greenhouse. I think it will make a difference in the cold air infiltration in winter, and I think it also makes the panel clips grip better. However, it took longer for me to weatherstrip each opening than it did to attach the panel, so it does take time. Also, as mentioned above, the foam weather stripping might complicate adding screws to the top and bottom edges of the panel.

Steps to Attach the Panels

We live in a windy place. Sudden breezes are the norm; windstorms are common. Until now, the empty greenhouse frame didn’t present any wind resistance. In our windy location, however, adding the panels changes everything. I didn’t want to take any chances by putting the panels all in place one day and then screwing them down later. So, we generally followed this order for each panel:

1. Apply weather stripping to greenhouse frame opening.
2. Remove protective clear plastic from panel.
3. Attach panel with clips
4. Add screws to panel

The Roof Panel Length Problem

Mysteriously, some people report having this problem, and others don’t. We did.

On page 16, the diagrams direct you to make sure the top of the roof panel (part 60) is tucked under the edge of the roof crown (parts 10,11) in the designated gap. And, it tells you to make sure the bottom of the panel extends past the edge of the gutter. Our panels weren’t long enough to do this.

If we extended them past the edge of the gutter, they wouldn’t stay in place at the roof crown. If we tucked them securely into place at the roof crown, they fell short of the gutter, by as much as ¼” in some cases.

In fact, this whole "extending over the gutter" directive doesn't make sense to us, since the gutter is a bit higher than the aluminum ridge that the panel sits on. If we did slide it down to extend over the gutter, the panel would have to actually turn up a bit, at the end, instead of laying flat. The way ours fit, falling just short of the gutter, they laid nicely flat and in place, as you can see in the photo above. (You can also see a bit of morning condensation in the panel channels, but that evaporates pretty quickly.)

If the way the panel fits above is truly incorrect, we've wondered if there was some tiny final adjustment at some point during the roof assembly that we missed. We really have no idea. Maybe they just ship out short roof panels on occasion! The mystery continues.

I noticed others used aluminum tape to cover the gap at the bottom of the panel, to direct the rain water into the gutter. I did the same, as shown to the right. I think it will work fine.

(Update, May 2008.) After 7 months in our hot sun, the aluminum tape is still adhering beautifilly to the tops and bottoms of my polycarbonate panels (where I used it to keep moisture, bugs, and dirt out of the poly channels.) However, the aluminum tape I used to guide rainwater into my gutters (above photo) is no longer adhering to the roof, so I'm replacing it. Some kind of tape with UV protection might last longer, but I can't find anything like that locally. I'm using clear duct tape (Lowes) to bridge the gap between the bottoms of my too-short roof panels, and the gutters, and we'll see how long that lasts.

I also used aluminum tape to cover the seams of the tall polycarbonate panels on the back wall. The tallest panels on the back wall are joined together by two (VERY tiny) s-shaped clips. After these panels were secured, I covered the seam between the two panels with some aluminum tape to keep my winter heat from escaping.

However, here's one thought: if you're going to be adding an exhaust fan to any of the tall panels in the back wall, as I did, don't tape these panels together until after you do that. You may want to remove the panel to cut the hole for the exhaust fan, and if you've taped it all in place, you'll be annoyed.

Here’s a photo with the roof panels completed, and both of the long walls. Because of the added time spent weatherstripping, we didn't finish installing all of the panels in one day. We decided to leave both ends of the greenhouse open overnight, instead of building a "box" closed on one end that might catch the wind. (Did I mention it's windy here?)

Next day, panels are all complete. And, it looks like a greenhouse!

Remember that old joke defining a boat as a hole in the water into which you pour money? Turns out greenhouses are the same thing, but they don't float.

If you'd like to see how we continued to spend money on further enhancements, click here to go to Part Seven: Greenhouse Enhancements.


Oldma said...

Having trouble posting for a few days. Trying again:
OWG, I am so happy!
I got it all done but the last wall. I had to order more clips. But, when the Fed-X man comes, it will only take a half hour to finish. Thank you so much for all your help and encouragement. I worked hours putting the base down, four corners and the front and back supports. I was ready to throw it away. Hubby found YOU on line. I saw both front and back support were put up wrong ... I wrote in with a problem and YOU answered. THANK YOU SO MUCH!
BTW, I put it on my porch. It is great!

mudhouse said...

Hi Oldma, you are very welcome. I'm so glad you were able to find the solution to your problem!

You might also enjoy reading the Greenhouses and Garden Structures forum on GardenWeb ( Lots of very good info there about greenhouses, and helpful people with years of experience. Also, an active group of Harbor Freight greenhouse owners post there. Enjoy your greenhouse,

doc said...

Hello again Sheri,
I had left a comment/question in the installing windows section. Had another question here.....
Trying to understand the advantage of putting the aluminum tape on the ends.....and then putting holes in it.
Is this not basically back where you started (open channel ends) and defeating the stated purpose of sealing the panel? If effectively sealed from bugs, dirt, and moisture with application of tape ...why not just leave it that way??
The screws/washers and the weatherstrip.....easy to see the advantages and have purchased already! Great ideas.

mudhouse said...

Hi doc,
On this point (and most others in my blog) I followed advice posted by others, since this is my first and only greenhouse. The tape is solid at the top, so as to completely block dirt, water, and bugs from moving into those small channels. (There are some truly awful photos posted on the GardenWeb greenhouse forum of what polycarbonate can look like after the channels have filled up with green slimy growth and various bug homes, and my housekeeping skills are poor enough as they are.)

On the bottom of the panel, where the tape is pierced, the idea seems to be to make the holes small enough so insects can't easily move in, but large enough to allow moisture or condensation to leave if it does exist in the channels. Charley's Greenhouse Supply sells a breathable polycarbonate tape that's a more presentable version of my (cheapskate) pierced aluminum tape. (It probably lasts longer than aluminum tape, as well.)

As you suggest, I also have a sneaky suspicion that the venting on the bottom is not absolutely critical, but I haven't had the chance to prove it one way or another.

I suspect this is more critical in wet climates. To be honest, in my hot arid climate, I'm not sure I needed the tape protection at all, but when I saw photos of folks trying to dig green goo out of the ends of their panels, I decided "better safe than sorry."

bluetumb said...


Is it 560' of weatherstripping including doubling up at top and bottom? Found 3/16 x 3/8 x 17' closed cell foam for 2.49 with 20% discount @ Lowes. Not sure about foam because it doesn't state waterproof, but does state high density. Is this stuff ok?

mudhouse said...

bluetumb, you have me, because I'm actually not sure if that 560 feet of weatherstripping included doubling up at the tops and bottoms of panels or not. It's been a few too many years for my memory, and my notes aren't clear. I'd say possibly not, since I think I may have discovered that the tops and bottoms needed thicker weatherstripping while I was doing the install. I'm sorry I can't be more precise.

The MD High Density Foam Tape Weatherstripping you linked to, from Lowes, is exactly what I used about a month ago when I replaced my roof panels. It should be fine. Mainly I wanted to avoid the very cheap foam weatherstripping that compresses very easily and can soak up water like a sponge when wet. I noticed the packaging no longer says "closed cell" or "waterproof" like it did years ago. Sorry for any confusion.

This time I bought 3/16" thick weatherstripping for the sides of my roof panels, and used 1/2" weatherstripping on the bottoms of the roof panels (no weatherstripping was used on the top of the roof panels, since they fit into the groove at the roof peak.) Or you can double up on the 3/16" thick stuff for the tops and bottoms instead of buying 1/2", that works too...whatever you need to do to close down the air gap between the panel surface and the aluminum frame.

Applying the weatherstripping is admittedly a bit of a pain, as it slows down the panel installation process, but I really do think it makes a difference in the seal you get at the edges of the panels. I hope it works well for you too!

bluetumb said...

I would have thought there would have been more people finding this blog site lately. It has been very helpful and after I complete the HF greenhouse I could give you some other details if you want to update it. As for now thanks and Happy Thanksgiving and blessings upon you for this undertaking.

mudhouse said...

I do hope you will stay in touch, updates and helpful info are always welcome! You can post here or email me at Good luck with your build!

Kevin Byrd said...

As to your suggestion to screw the panels in, what type of metal are the screws? Steel and aluminum don't get along and I assume the screws you are using do not rust?

mudhouse said...

Hi Kevin,
I believe the screws we bought at Lowes are plated steel. Could be the minimal contact area, could be our climate, but after over six years, we've not noticed any problems with rusting or reactions at the points where the panels are screwed to the frame.

Dave Stroble said...

Just picked up two of the greenhouses for $510 per. With tax it cam out to $540 each. The 25% off coupon really helped! Living in WA state, it can be windy and wet. Your instructions will make this project successful and I am eternally grateful for your work in posting all this wonderful. Thank-you so much!

mudhouse said...

Hello Dave, congratulations on your good buys, can't beat that price!

Harbor Freight has redesigned and changed a few parts in the kit since I wrote this blog six years ago, and there are apparently old and new versions of the kit still being sold. The changes mostly seem to affect the doors, and the base pieces. So if my instructions for those areas seems to differ a bit, that's why. Hopefully it won't cause you any problems.

Best of luck with your build!

Phil S said...

Is there a certain sequence to installing the roof panels? I'm not sure I can reach across everything if I just start at one end and work down that side.

mudhouse said...

Hello Phil,
I'm sure there is more than one way to do it.

We think it's best to either:
1) install the center panels first, including those that fit around the windows, and then work outwards towards both ends of the roof, or
2) start at one end of the roof, and work your way across to the other end.

With either method, at the end, you'll end up with the ladder on the outside of the greenhouse, reaching to clip the outer panel in place at the edge of the roof.

The only thing that would not work is to do the end panels first, and leave the center roof panels for last.

We've put roof panels on twice now, once when the greenhouse was new about six years ago, and again about two years ago when we had to replace the roof panels as they had deteriorated from sun exposure.

I will be honest with you that there are a few spots that are really a challenge to reach. It's not my favorite part of the build. My husband is over 6' tall, and fortunately has long arms. He was able to place some of the final clips in the tough spots, using an 8' tall step ladder, that I simply would not have been able to reach myself (5' 6"). We used two step ladders, 6' and 8', and could not have done it without the 8' ladder, if that helps.

Virginia said...

Hello, I have the 6x8 green house from HF. I read in some of the post about bugs getting inside the panels and them turning green. I however could not find where you 1st touched on the subject and how to fix the problem. Help

mudhouse said...

Hi Virginia,
Scroll all the way up to the very top of this page, at the start of this section (Part Six, Adding the Panels.) I talk a bit about adding tape to the top and bottoms of the panels, to keep bugs and moisture out of the tiny channels.

When I wrote this blog, I used aluminum tape from Lowes (cut to a thinner width) to seal the panel ends. In my very hot sunny climate, I found the aluminum tape started to come off after about two years. Now I use clear duct tape instead, cut to 1/2 width, to seal the panel tops and bottoms.

Conventional wisdom is to allow the bottom of the panel to "breathe" and let moisture escape through holes in the tape. That's why I show piercing mine, on the bottom, in the photos. I've learned this really isn't necessary in my dry climate, so now I just seal both ends.

You can also buy a tape specially made for sealing the ends of polycarbonate panels through greenhouse supply companies online. I think these tapes are usually breathable (slightly perforated.) They might have a much better adhesion than my cheaper alternatives.

I have read that some folks actually use caulk on the panel ends, to seal those little channels, but I can't imagine how a person could do that without making a big mess! I think some kind of tape is easier to apply, personally. Hope this helps.

puredoller said...

I've been looking at this greenhouse for about 10 months and finally got the 6x8! It's $400 at Harbor freight but it's always on sale for $300. A couple weeks ago it was $260 during a 'get ready for spring sale' and I'd never seen a lower price so I almost bought it but I am glad I didn't! I got it two days ago for $199 during a 3 day 'parking lot sale'!!! I found your blog and I am SO GLAD I DID! I printed all your pages for easy reference in the yard while I am building! I also lov eyour sense of humor about it all. It makes reading boring information fun! lol
Thanks so much for this!

Cindy Clemmens said...

So am wondering how much of the greenhouse can I assemble when it's windy? The base obviously and figure I can tape and put the weather stripping on the pannels but not sure how far I can go on the rest of the frame? I plan on putting 2x4's at the studs. Thanks again.

mudhouse said...

Hi Cindy,
The frame itself has very little wind resistance, so we don't think you will have any problems working in the wind, until you start to install the panels.

Installing the panels in bad wind might be a good way to take up hang gliding, accidentally. ;-) So wait for calmer hours to work on adding those, and you should be fine.

So aside from a possible bad hair day, you should be able to make good progress on the whole frame.

Cindy Clemmens said...

Thank you again so much for the advice.

Finally we are having better warmer weather but the april showers is getting annoying already. lol But picked up my lumber yesterday and got it all hauled to the back yard today and got the fire pit moved as well. lol and tonight got the long wall side panels and roof panels taped and weather stripped and the two vent windows assembled.

Just very nervous about getting the foundation and frame level and square.

mudhouse said...

Hi Cindy, just take your time, and check things as you go. You can use a level and a square to make sure things are right.

For me, it's much more stressful to try to rush a project like this. I'm sure you'll do fine, just work at a pace that feels right to you.

Cindy Clemmens said...

Just found the level and the square earlier today thankfully. Feels like i've been waiting forever. lol

Take care and hopefully soon i'll have a done pic


Fran Lebowitz said...

Hi Mudhouse,
Thank you so much for your helpful blog.
I'm putting my panels on now, and noticed that the front panels on either side of the sliding doors don't have any brace to rest on at the top. The sides and bottom are supported, but there is nothing at the top. Anyone have this problem? I suppose I can get some aluminum channel and make my own brace, but I didn't see this mentioned anywhere. Have I missed something?
Thanks for advice.

mudhouse said...

Hello Fran,
I'm away helping a family member recover from surgery, but I have a very fuzzy memory of what you are describing. It could be that the way the top aluminum door plate is designed, it doesn't quite contact the top of the panels as much as the greenhouse frame does on the bottom and sides, but I'm afraid it's been too many years for me to remember this detail clearly.

I do know we did not have to add any bracing, and I have not had any reports of others having to add bracing in this area, either. I'm guessing (?) that the rigidity of the panel itself will resolve this (in other words, if it doesn't rest as firmly on a surface directly behind, at the top, it's still OK.)

When I get back and have access to my own greenhouse, to check this area, I will try to post again. I'm sorry to not have a better answer for you right now.

Passionflower said...

I just constructed my 6x8 HF greenhouse this weekend before finding your blog. Glad I did find it tho - will use several of your enhancement ideas. Thanks!

My question is where to find extra clips. I may have missed your suggestion. I only found a place out of England which seemed a bit far. Any suggestions? I live in Portland OR.
Thanks for your help.

mudhouse said...

Hello Louise,
Harbor Freight only sells the clips through their toll free number; they don't stock them in their stores, or sell them on their website.

Scroll back up to nearly the top of this page, and look for the blue header that says "Modifying the Panel Attachment" (right next to my photo of my hand holding the clip.)

I have the phone number, parts numbers, and quantities listed there, to make it easier when you order by phone. Best of luck to you,

Jim Springer said...

I must be missing something simple on installing clips. I do not understand how to do it easily. Do you put the clip on the panel and then push the panel towards the frame?



mudhouse said...

Hi Jim,
No, you set the panel in place into the framework opening, and then use the clip to secure it to the frame. The clips won't stay on the panel itself; they are held in place by the springy tension they apply between the panel and the aluminum frame.

This is one of those annoying things that is very simple to do in person, but crazy hard to explain in typed words (so bear with me.)

First, for a visual, go to part 7 of my blog here:
Part Seven Greenhouse Enhancements
...and scroll down about 1/5 of the way down this page, to find the section I have titled Aluminet Shade Cloth Screen Panels. The fifth photo in this section shows a clip installed, up close.

When I install these, I position both of the free ends (let's call these the feet) so that they are captured by the track in the aluminum frame, as shown in the photo. While keeping those feet in place, push on the rounded center of the clip, sliding it across the surface of the panel, moving towards the track. You'll have to push a bit hard. This compresses the clip, and when you push the clip to the edge of the panel, the two "shoulder bends" will suddenly pop behind the panel edge, and the center of the clip will remain pushing down on top of the panel.

The feet are captured by the track, the two "shoulders" slip just behind the edge of the panel, and the rounded central portion of the clip winds up bearing down with a bit of pressure on the outside surface of the panel.

I know that is probably as clear as mud (it really is super simple, but the words make it sound terribly complicated.) I hope this helps a bit. Please let me know if I've only made things more confusing!

Hayley C.E. said...

Your blog helped us tremendously while building our 10 x 12 greenhouse, thanks! My one question is how in the world do you reach the window gadgets to open and close the windows at such a height?

mudhouse said...

Hello Hayley, well, I don't have a good answer for you. I used a small two-step aluminum step ladder for a while, to open and close the window vents as needed. This got old very quickly, especially because my greenhouse is filled with cacti, and I was teetering over benches full of scary spines, when I was up on the little step ladder.

Unlike many HF owners, I eventually gave up on my roof vents. In my location, the prevailing winds could pick up the roof vents just a tad, even when they were in the "closed down" position. Although the vents raised only a fraction of an inch, it was enough for a constant bang-bang-bang vibration on windy days. This eventually caused my poly panels in the windows to wiggle out of place. I caulked those in, but the annoying banging continued. I finally wired them shut, and gave up.

I could only get away with this because I installed an exhaust fan for cooling, and I also replace the south wall in the summer with screens. I don't really recommend this because normally roof vents are very important for cooling.

What I should have done is to look into automatic roof vent openers. These are non-electric openers you can purchase from greenhouse supply companies. They have a wax-filled tube that responds to temperatures, moving an arm to automatically open and close your vents.

Harbor Freight makes some, but to be honest they have poor reviews in the forums. (You can go to the GardenWeb greenhouse forum, and search the archives for posts on Harbor Freight vent openers.)

Bayliss and Univent are two brands that get better reviews. I eventually removed my roof vents entirely, when I had to replace the greenhouse roof panels a few years ago. So I don't have any experience with the automated openers, but many folks speak highly of them.

Hope this helps!

jake said...

AWESOME Information!! THank you So MUCH!!

mudhouse said...

You're so welcome Jake, glad it helped!

JoAnn Gonzales said...

Hi mudhouse. First of all let me thank you for this bountiful information! You have helped save my sanity. Just an FYI on tape. Gorilla Glue now has a waterproof tape that is clear. It's called Gorilla Clear Repair. That's what we used to seal our panels. In the newer kits, both top and bottom have to be sealed. We are just at the point of reinforcing before adding the panels, but have had so much rain, I've been able to tape all panels, build the vent windows and door. Just waiting for clear weather to get back out there. Once again, THANK YOU for taking the time to do this blog. It's a Godsend! JoAnn

mudhouse said...

Hi JoAnn, I'm so glad you've found some help here. I realize that Harbor Freight has changed some parts of the kit (and manual) since I wrote this blog, so I hope there aren't too many differences that cause confusion.

Your tip about the waterproof Gorilla Clear Repair tape is much appreciated. I'll be sure to use that when I tape my next set of panels. I have used the Gorilla brand duct tape and it's better than average, so I'll bet their clear waterproof tape will be perfect for the job. Thank you!

Hoping for clear skies for you, and a successful completion of your build!

Fran L said...

I"d like to second Joann's comments. Your blog has been terrific, and almost a necessity since Harbor Freight's manual is quite basic, to say the least. Thank you for the great photos and suggestions for upgrades. Those of us in windy areas surely have much to be grateful to you for.


mudhouse said...

Thank you Fran, glad this is helpful!

I really hate to hear about wind damage to these structures, and I am eternally grateful to the early owners of the HF 10x12 greenhouses that figured out many of these necessary "fixes", and posted them on the web to help the rest of us.

We are going into our 8th year now with no wind damage...thanks to screws in the panels, modifications to prevent flexing, and extra clips.

Good luck with your build, and happy growing!

Abraham said...

Hello, and thank you and all the other people who put their two-cents in to build this greenhouse. I am almost finished with our 10x12 HF greenhouse. We doubled up on the clips,added the metal screws to the panels,taped the panel ends and added 1" EMF pipes to reinforce the frame. I just have one question about modifying the sliding door structure. Le wrote a tip awhile back about adding some bolts, nuts and weather stripping to keep the doors closed so you don't have to clamp them. After the doors are closed you slide a couple of nails through the holes in the bolts and it keeps the doors closed. I cannot fully visualize what that looks like. Is there a pic or diagram of this anywhere? Thanks, Abraham

mudhouse said...

Hi Abraham, I don't have a photo or diagram of Le's solution (sorry.) I am in the camp of those still using the unglamorous clamp solution (one high, one low.)

Fran L said...

Abraham, I use a swivel hasp to keep the doors closed. It works well. Found it at Walmart, but you can find them at most hardware stores. No lock is needed, just turn the swivel piece to secure it. Email me for a photo; can't figure how to attach one here.

Walmart #: 551496840
Bulldog Hardware 6" Swivel Hasp, Zinc

Good luck,

Samsunshine Levy said...

I also live in New Mexico, like MudHouse, but I'm in Santa Fe, at 7,800 ft elevation with a LOT of ultraviolet exposure. Our upper panels pitted everyhere on the outside and all non-north facing panels became yellow & brittle after about 18 months.
FYI, As of March 2016, it appears that HF is no longer selling a full replacement set of polycarbonate twin wall 4mm panels.
If you call HF regular number/ordering dept, they have individual panels, sub-parts numbers 55 through 64, at a cost of $10-$18 each. As there are 51 separate panels, it would cost more than the entire greenhouse to get a complete replacement set. I'm looking for some source to get these at a better price, but have not been able to find one.
It is recommended to upgrade exterior protection with clear UV resistant film (can use either foil tape or transparent duct tape) on the outside of south facing and top panels. Here's an example of a 4 year UV film for $48 shipped:

mudhouse said...

Thank you Fran!

And thank you also, Samsunshine, for the info about HF not selling replacement sets of their polycarbonate panels.

We're looking at replacing most of our panels this summer. This will be the second time we've replaced the roof panels; the last set was fatally wounded by a hail storm in October. Your suggestion about facing the panels with greenhouse quality polyethylene makes sense. It does seem like that would certainly extend the lifespan of the Harbor Freight panels. We used the same product over our (damaged) greenhouse roof to get us through the winter, and it has held up fine. I do think it affects how much light comes through the panels, slightly, but that's not a problem in our state!

I'd love to avoid doing a re-roof for (dare I hope?) another ten years or so. I'll probably bite the bullet and order sheets of 4mm polycarbonate from a greenhouse supply company. Most twinwall polycarbonate sold elsewhere (with true UV protection) has a ten year warranty, so it should last much longer than the Harbor Freight poly panels. I'll have to use my old panels as templates and cut them from the new material.

The north wall of our greenhouse (covered with insulation, and protected from the sun by our house) still looks like new, so I won't replace that side. I need to do a more careful calculation, but I roughly estimated that 6 sheets of 4' by 8' 4mm twinwall polycarbonate might be enough for us.

If it helps you, in October 2015, I did an online chat with, and they quoted a total price of $432.48, for six sheets. That was $311.70 for the poly, and $120.78 for packing and shipping, to me here in Las Cruces. I actually thought the packing/shipping would be more, because I believe it has to be crated, but that's what they quoted. I'll re-confirm it all with them in the next few months when I'm ready to tackle the project.

Samsunshine Levy said...

I'm looking at replacing my south facing wall and the south facing roof up here in Santa Fe. Interestingly, Solexx (10 year UV warranty supposedly) comes in 146" (just over 12') lengths. By my calculations (I have to go out and measure the panels), 146" is EXACTLY the height of one wall panel plus one roof panel - assuming you make the cut perfectly. One 4' wide sheet does two segments/4 panels from making only three straight cuts. 3 pieces will re-do the entire south face and roof (or re-do an entire roof-only). 3 pieces of XP 3.5mm, delivered is $243 from (also from Staples/Wayfair/Sears/Walmart online for a few dollars more). That is basically the SAME price as HF is currently quoting for one-at-a-time panels ($16 wall, $14 roof, not including tax & shipping), for something that could last five times as long! Pro 5mm is $58 more, though yes I know I'd have to compress it to squeeze in at ridgeline upper corners.
Then I can optionally add 50 glazing clips ($9.67 amazon) and a roll of UV treated plastic (above post, also from Amazon) and I've still got plenty of foil tape.

mudhouse said...

Yes, I've looked hard at Solexx too! According to the Solexx website, it also has a higher R value (insulating ability) and lower U value (heat loss) than 4mm twinwall polycarbonate. That's appealing.

I only have two concerns with Solexx. One, it's a translucent white material, not clear, and I'm not sure I'd like how it looks; I guess that sounds vain, but our GH is very visible to many neighbors. More importantly, I wonder if it would cause me to replace my 60% Aluminet shadecloth on the roof with a lower percentage. The white material should screen out some of the intense sun, but coupled with my current shadecloth, it might be too shady for my sun-loving succulents.

Second, I add and remove four of my south wall panels, as night temperatures dictate, in spring and fall. It's really fast for me to pop in the panels for a cold night, and replace them with my screen panels for warm daytime hours. I have to do this "panel dance" for a short time each spring and fall. (As soon as the nights get warm, the screens stay in 24/7.)

The Solexx panels, I think, would be floppier and not rigid like the polycarbonate panels. So, I think those four panels would be harder for me to pop in and out. This of course wouldn't be a problem for most people, who don't need the flexibility of being able to swap panels with screens quickly and easily. It's just been part of my solution for dealing with our high temps, down here in the broiler-oven part of our great state. ;-)

I've even thought about buying Solexx for the roof, to see if I could eliminate shadecloth on my roof entirely. And buying clear polycarbonate for the sides, to look all sparkly pretty for my neighbors.

Decisions, decisions. Argh! It's not easy.

mudhouse said...

Just posting a correction here, to my post abov,e about the number of 4' by 8' sheets of twinwall polycarbonate needed. Sorry; I misread my notes when I posted above; I'll need six sheets (about $432) to replace my roof alone, and of course much more to replace the deteriorating side walls. So, not an inexpensive proposition, no matter how you slice it.

Joseph said...

Hi Sheri, First of all thank you so much for your blog and all the amazing pictures, feedback, design improvement, etc. I'm about to put up a new HFGH 10 x 12. I'm considering using solexx over the whole thing. I may use the existing new panels additionally as extra insulation but would also consider selling them if any other nm folks would like replacement panels since there not available any more. I live up in Taos. I bought the greenhouse last fall and it has been stored out of the sun so all the panels should be perfect. I'd sell them for the old harbor freight replacement price if anyone is interested.

mudhouse said...

Hi Joseph,
If any New Mexico folks contact me looking for a set of 10 x 12 Harbor Freight panels, I will be sure to post back here, to let you know. Best of luck on your build, in beautiful Taos!