Deck greenhouse questions/concerns
Sorry for the novel. I tried about a million times to shorten this, but I wanted to explain what we’re doing before it gets ripped apart. Honestly, that’s kind of what I’m hoping for so we don’t make any huge, unfixable mistakes.
My dad and I are building a roughly 5’x10’x7’ greenhouse off the back of the house for his lemon and grapefruit trees over the winter. He was a home builder his whole life, so I trust him completely when it comes to construction. The problem is that I know very little about greenhouses, and he probably knows even less, so I’m looking for some outside opinions before we get too far.
The roof will be a single sheet of 16mm “triple wall” polycarbonate. The pitch is pretty shallow, so I’m wondering how well it will handle snow/ice. The sides will be insulated glass doors two double doors and one single door. His idea, which could either be brilliant or a complete nightmare.
The deck underneath is mostly new. The 2x10 joists are about 40 years old but in surprisingly great shape. He added supports every 2 feet, replaced the 4x4s with 6x6s, added additional 4x4 supports, and bolted it into the house in a bunch of places.
We actually sit/walk underneath this area, so we’ve tried to beef it up as much as possible. I can post pictures of that if needed, although I’m guessing structural questions are probably better suited for r/decks.
We’re planning to insulate underneath with foam board. On top of the Trex we were thinking Tyvek or another impermeable layer, then a rubber/vinyl mat. I’m also wondering if the floor should have a slight pitch toward a drain to deal with condensation/watering.
The big questions I’m hoping people can help with:
How realistic is it to overwinter lemon/grapefruit trees in a greenhouse in Zone 7? The deck faces southwest and gets a ton of sun, and being attached to the house should help with heat retention, but I’m assuming supplemental heat and possibly lighting will still be necessary.
How do we balance ventilation/humidity control with trying to retain heat in the winter? We’ll have an exhaust fan, and the doors have screens, so summer seems easier.
Should we add a drain in the floor?
How strong is 16mm triple-wall polycarbonate for a roof, particularly with snow? Is our pitch too shallow?
Would wrapping the outside with another layer of plastic or some other insulation actually help?
Any obvious greenhouse-specific problems with the materials/design that I’m missing?
One thing I’m particularly concerned about is the dryer vent. It’s a gas dryer, and my dad thinks venting it near/into the greenhouse will help heat it. I’m pretty sure intentionally putting a gas dryer exhaust into a tiny enclosed room is a terrible idea because of CO and moisture, not to mention the heat/fire concerns. He seems less concerned than I am. 😂 There will at least be a smoke/CO detector, but I’m pushing for the dryer to be properly vented somewhere else and using a safe dedicated heat source if we need supplemental heat.
Basically, I realize there are probably about 47 ways this thing could become a death trap, so I’d rather find them now while we can still change things.
My dad wants to keep his citrus trees in here all winter, and I’m trying to figure out what we need to do to make that realistically possible.
Any advice, criticism, or “absolutely do NOT do that” comments are welcome.
My dad has been growing in ground trees so I think he will be able to keep them pruned to fit but the size and other concerns I have make me think, it better suited as a greenhouse for keeping cold tolerant plants through winter, maybe it will be warm enough for some other vegetables but I just think it’s too small and ill prepared to keep citrus trees and he will have to keep driving my mom crazy by keeping them inside. At least she got creative last year and in lieu a Christmas tree lit and decorated the lemon trees.
Thanks for reading this far and I’d appreciate some constructive criticism