Gable End Vent for My HFGH

Posted by @Eric4home on
This article was written with the home greenhouse gardener in mind and especially the Harbor Freight Greenhouse projects https://garden.org/thread/view/21716/Harbor-Freight-Greenhouse-projects/?offset=940#end_of_thread (HFGH) thread, but would actually be adaptable to almost anyone with a similar frame greenhouse.

Further modification to my HFGH

Since I use a solar blanket in the winter and shade cloth in the summer, effectively blocking my roof vents, I needed more ventilation in my greenhouse on sunny days. So I built a gable end vent. They are often used on commercial greenhouses.
I started by visiting a local welding and plumbing shop that retails structural metals. I bought two 48" and one 36" piece of aluminum angle, about 3/4-1" on a side. I also had two 24" pieces on hand. To the dealer, these were basically ends or scrap, so I got them for about $15.
I cut 2 pieces to 24" to mount on the inside of the studs and 4 pieces to create a 22 1/2 x 16" frame for the vent, which I took to a local welder who made my sturdy frame for $20.
I went to Ace and bought a 2' piano hinge. Mine is nickel plated, but if you shop around, stainless steel (ss) is available. This was cut and bolted to the frame with 4 stainless steel bolts.
When it came time to mount the frame, I added bolts to the T slots in the studs. Then I cut two 3/8" x 1" x 22 1/4" shims from scrap PT lumber. These are used between the polycarbonate and the interior frame. These are held in place by ss self-tapping screws. A section of polycarbonate was cut out, leaving an inch or two extra at the bottom. The upper frame was drilled to mount the hinge, and after I loosely mounted the vent frame, it was slid up so that the hinge was covered by the polycarbonate. I also added a 3" wide strip of roofing rubber as a flashing for the vent. This was inserted under the poly and held in place with silicone. Everything was aligned and tightened in place.
The lower frame was bolted in place and the shim was added The poly was cut to allow the vent about 3/4" overlap.
All cut polycarbonate was taped on the top and bottom with aluminum tape, the same as with initial construction, and fixed with silicone to the frame. The vent panel was similarly mounted.
I mounted one of my Bayliss auto openers to the vent and frame and now have a sturdy vent that opens freely and closes soundly. I will be adding foam stripping to the sides of the vent and vinyl weather stripping to the bottom edge.

Tip: Adding bolts to your stud tracks is easy. Just take a large drill bit 1/2" or so, and at about a 45-degree angle, carefully cut the track edges away so you can insert the bolt head into the T track. Be sure you do this where it will not interfere with what you want to mount, such as a shelf, brace, or frame. The 2 lower photos show this.

This vent allowed my neighbors to come care for the GH while we were away without significant overheating until they arrived to open the door if needed. Since I already had the Bayliss opener, the entire project cost about $45.

Should I need additional venting, I will construct a vent for the other gable and possibly add an exhaust fan with an inexpensive inline thermostat, but that's another idea.


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