As far as I know, you shouldn't have to caulk the roof panels in your HFGH to make the roof watertight. Someone may correct me, but I don't recall reading about anyone who had to caulk all the roof panels to correct a leak problem.

I used foam weatherstripping on all four edges of my panels, roof and wall, as I installed them. I did it to get a good air seal to avoid heat loss during the winter, but I suppose the good seal provided by the weatherstripping might also help keep things water tight. The foam weatherstripping was a bit of a pain to apply, but it really does help with the seal, and I like it because I can still remove any panels if I want to, unlike panels that are caulked in place. I haven't had any roof leaks, and mine is going on three years old. However, I honestly don't recall reading about this as a problem among folks who didn't use weatherstripping, either.

Is it leaking at the four corners, where the roof touches the corner wall posts? I had some big gaps (and leaks) at the top of all four corner posts, after everything was assembled. I fixed that with little folded over pieces of weatherstripping, covered with aluminum tape, and sealed over with clear silicone caulk. It wasn't very elegant, but the gaps were fairly large, and that solved the problem. No more water running down the corner posts during a rain.

I also caulked my roof window panels into the roof window frames, but not because of leaks; it was because the poly panels for my windows were a bit too small to fit snugly in the frames, and they tended to shift around in the window frames in high winds. Those are the only panels I've used caulk on, in my greenhouse.

I'm hoping someone else will chime in here, since this isn't a problem I've experienced on my own HF 10x12.

Did you order extra clips to install the panels, or did you only use the clips supplied with the kit? I'm just trying to think of anything that might help improve contact between the roof panels and the frame. My roof panels are secured with extra clips (and a screw into the frame, for protection against wind loss.)

I didn't buy any extra clips, but I did screw the panels into the frame. I'm not sure exactly how the water is getting in. I don't see any obvious gaps between the panels and the frame, but the water must be seeping in somehow, right?

I will try to get a tall ladder and pour a bucket of water in different spots. The first time I used my hose, and this weekend we had a down pour!

Anyone else have any thoughts? I would be curious to know how many installed the weatherstripping. I may be the only one that was silly enough to check the forums AFTER most of the greenhouse was up! :-)

Although I'm a big fan of addings screws to the panels, I don't think screws do much to help the seal of the panels to the frame at the panel edges. Seems like additional clips would help the panel edges to be pressed more firmly to the greenhouse frame, which also helps the panel edge to be less easily lifted by a bad wind, in addition to lessening the chances of a leak.

In case you decide to try the weatherstripping idea, this part of my blog has some photos about how I did it (there are several ways, including sticking it to the panels, or to the greenhouse frame) and also talks about adding extra clips:
Part Six: Adding the Panels

I hope others will chime in too!

I will try to add more clips to a few of the roof panels to see if that works. I may also try some silicone clear caulk.

I was REALLY hoping some others would chime in with their water leak stories! :-(

I don't think silicone will seal to the polycarb... My 10x12 drips once in awhile when it rains especially around the vents.....but it's sort of a fact of life that these things may leak. ;-)

Here is a link that might be useful: my GH

web4deb is right--it's not realistic to expect that this thing can be made waterproof (the vents especially; not designed for water resistance). But good luck if you wanna try.

Thanks for the replies.
How badly is it supposed to leak? I'm worried about putting a heater inside with all of the rain.

Or do I really not need to worry about that?

If you have leaks or not....anything electrical should be plugged into a ground fault circuit.

You don't say where you live but since you mention a heater I will assume you are where you will need heat.

I live in northern Indiana and so I wanted to make my GH more easy to heat so I installed a pool cover on the roof but instead of using ropes or that type of hold down which is sure to fail in the wind I used aluminum angle pieces and screwed them to the roof ends to hold the pool cover on.

This will stop your leaks it will make it much better to heat and will protect the roof from sun damage.
I just lapped it over the ends used self tapping screws to install the angle pieces they trimmed off what was hanging over.

Ok, so the HFGH isn't waterproof. Oh well! My friend really thought that caulk with help with any major leaks, so I went ahead and caulked the roof. Also, here in Central Louisiana, it get's very hot! I put one of those commerical temperature sensors and found that it was getting 130F in there!

I've since closed the vents on the roof and put a 70% Aluminet shadecloth that comes down a little less than half-way. I've got a 20" fan circulating the air a bit, and I'm keeping the main doors open. It's dropped down to under 110F now.

I am now going to look for two windows I can place on either side and an exhaust fan to place at the top to help more. I'm also thinking of getting a evaporative/swamp cooler to try and get the temps down to a reasonable 90F.

Thanks for all of your help!

Here is a link that might be useful: 70% Aluminet Shadecloth