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