Sealing double wall polycarbonate after the fact

[MoonShadows]

After a year of using my greenhouse as nothing more than an expensive seed starter, I want to learn about getting an earlier start and extending the season longer. From what I have read, this will entail sealing any leaks, insulating, an alternative heat source and a few other things, but before I begin, I realize I have one major obstacle which if I can't rectify is going to put a real crimp in my efforts.

We bought and assembled a Sunshine Gardenhouse Mt. Rainier 8 x 16 redwood and double wall polycarbonate greenhouse. Today, I was looking at some YouTube vids and learned that if the ends of the polycarbonate panels are not sealed off, there is no air lock and therefore no dead space to help the insulating factor. My problem is it appears my polycarbonate panels are "floating" (for expansion/contraction) in the redwood frames, but they were never sealed at the ends! (Seems like a poor design to me.)

My question...if I spend a small fortune on silicone caulking (most of which I'll wind up wearing like my friend @tbendl ) and I caulk around each panel both inside and outside, will the silicone caulking allow for enough expansion/contraction AND act as a seal to keep dead air in the panels? Seams to me it would, but want to bounce it off some others first. Thanks!

 

[headfullofbees]

Yes, silicone is both air and waterproof, but I'd use the mould-resistant bathroom type.

 

[MoonShadows]

Thanks. I plan to use the clear elastomeric silicone caulking for best expansion/contraction give. I spoke with the maker of my greenhouse, and they don't recommend caulking both sides because it might affect the expansion/contraction. I think I will just caulk the inside to cut down on any leaks, not worry about sealing both sides, and use Reflectix insulation...double reflective, double bubble insulation...on the north and east walls and clear bubble wrap on the east and west walls. I also think I am also only going to insulate 1/2 the greenhouse to see how it goes this first year. I will also use 5 gallon buckets painted black and filled with water as a heat sink in addition to the already existing 8 inches of gravel on the floor that I laid slate over. I have a small oil-filled electric heater for colder days/nights.

Any feedback is appreciated.

double reflective, double bubble for east and north walls

clear for south and west walls

 

[Gardening Girl]

I have been selling, installing and using polycarbonate sheets since 1993. I have never heard about sealing them to increase the insulating factor. I have dealt with many different manufacturers. They all recommend using a foil tape at the top of the sheet, a vent tape at the bottom of the sheets and a polycarbonate U profile over the tapes. The vent tape has "vents" in it for condensation to drain and you should drill 1/8" holes every foot on the bottom U to let the moisture drain. So, this is not a completely sealed off system like you saw on the video. Actually, I have seen customers where they sealed the sheets completely at the bottom and they had big issues with mold. As far as the greenhouse kit, sounds like the sheets are sealed off at the top and the bottom by the framing of the greenhouse which would be perfectly acceptable as well. The idea is to keep bugs, dirt, etc out of the channels. Polycarbonate does need room for contraction and expansion, so you don't want them too tight.

 

[Gardening Girl]

After posting this I remembered a product that I am pretty sure is what you were seeing. It is called Lumina Aerogel. It is factory applied and cannot be done at home. I saw this on a tour a couple of years back. It is a very expensive product and is hardly ever used outside of commercial skylight applications. It is applied inside the channels sealing them completely. It helps to increase the insulation factor and it helps to cut down on noise. I bet that is what you were seeing in the video. Sorry that I forgot about it earlier. I have only had one encounter with it, and it was quickly decided against using this product due to the cost.

 

[trapper79]

Hi all. does anyone have any personal experience in taping the ends of their poly sheeting? Foil top, vented bottom. I'd like to know of any problems or issues and also any positive notes.

Cheers
D

 

[Oliver Buckle]

Thanks. I plan to use the clear elastomeric silicone caulking for best expansion/contraction give. I spoke with the maker of my greenhouse, and they don't recommend caulking both sides because it might affect the expansion/contraction. I think I will just caulk the inside to cut down on any leaks, not worry about sealing both sides, and use Reflectix insulation...double reflective, double bubble insulation...on the north and east walls and clear bubble wrap on the east and west walls. I also think I am also only going to insulate 1/2 the greenhouse to see how it goes this first year. I will also use 5 gallon buckets painted black and filled with water as a heat sink in addition to the already existing 8 inches of gravel on the floor that I laid slate over. I have a small oil-filled electric heater for colder days/nights.

Any feedback is appreciated.

My feeling is that if you seal completely and put an oil burner in you will get problems with condensation and algae.