Greenhouse construction

Google "french drain". You should use filter fabric and gravel.

 

Weed barriers don't necessarily make good root barriers. If there's a constant source of moisture roots will eventually find their way through a woven or non-woven synthetic barrier. Treat this like a leach line - not a french drain. French drains are all about encouraging water to flow toward the trench and into the pipe - that's why the fabric is on the outside of the gravel between the soil and the gravel - to keep the soil from migrating toward the pipe. In a leach line water moves the opposite direction - away from the pipe - so there's no need to worry about soil migration. You should dig a trench wide enough and deep enough to accommodate gravel around the pipe. I'd recommend 2' wide and 2' deep or so if you can muster it. Put the perforated pipe in the middle of the gravel section, filter fabric on top only, and backfill with a few inches of soil. And for the pipe in the trench I would not use the coily stuff because the holes are pretty small. I'd use rigid pre-perforated plastic pipe 3" or 4" dia. - the orifices are 1/2"-5/8" dia. Rock should be 1-1/2" or 2-1/2" (not pea gravel). Orient the the orifices downward.

Roots will eventually find their way into your drainage system but unless the quantity of drainage is significant (shouldn't be in this case) the life of your system should be long. Aren't you moving to California in a few years anyway?

 

Ditto to the above -- you need to have sufficient drainage etc and you do need to have gravel/rock/weed cloth.

On the upside, you can tell exactly where my greenhouse "drain field" is in the backyard because the grass is absolutely incredible. People are always complimenting my husband on the amazing backyard, and it makes me chuckle. That grass gets some seriously good nutrients. And it is pretty obvious when you see the front yard that there is some "magic" happening to the back lawn.

 

In all of my greenhouses (moving is a PITA - this is GH #5), I have never provided external drainage, but let excess irrigation water simply soak in the ground. Obviously not ideal for a solid concrete floor...

I think your root barrier is a good idea. How well does your soil perk?

 

I would suggest digging a 18"x18 trench, lay down drain cloth, fill 6" with 3/4" crushed rock, lay either corrugated or ridged drain pipe with drain sock over it, then back fill with crushed 6" below grade, fold the drain cloth over the top of the rock, than back fill. You should have an 1/8" slope per feet on the pipe so water drains. I think 15-20 ft long will work.

 

You do want to make it long enough so if a water pipe breaks you won't flood the greenhouse too bad.... I would also suggest putting drain cloth over the drains to keep debre from filling the drain pipe.

 

I used to live near the New Jersey shore - my wife and I dug a 150' trench for a gas line to the greenhouse, put in the pipe and filled it in, in a day.

Another time I dug 36, 4' deep post holes with a manual clamshell digger after work. Sand is wonderful.

Then I moved to Bucks County PA, where I have no soil, but lots of shale. Pick-axe and crowbar are the digging tools of choice. (Which is why my tomatoes are in raised beds.)

 

I see deciduous trees. When the leaves come off, you'll need shade cloth.

 

Are you going to primer the OSB?

 

Probably roof only. By the time the leaves drop off of the trees, the sun's angle will be low enough that the light entering through the walls will be fairly well filtered by the atmosphere.

No "eventually" in the painting of the drywall. Do it right away. For one, white paint (flat is better than glossy, although harder to keep clean) will disperse light evenly throughout the structure, benefiting your plants, and secondly, it's best to do it before other stuff is in the structure, especially plants.

 

Don't stop with just primer; it's not made to wear, only to provide bonding. I would use, at a minimum, eggshell finish paint. Flat will get dirty and stay dirty-it is not scrubbable.

 

Agreed..... Use exterior paint as well.

 

If I could I would stop you from using traditional mildew resistant drywall.... You will still get mold no matter what you do to it in a humid greenhouse. It still has paper backing that's impregnated with mold inhibitors, which is what mold feeds on. Instead I would recommend fiberglass mat "dry wall". It has fiberglass backing and is made for exterior use.

 

Technically, flat paint is the best for light dispersion - the glossier it gets, the more like a mirror it becomes, leaning toward planar reflection to the floor - but I agree that it will get fouled in no time. I used a semi-gloss exterior enamel - several coats over exterior sheathing plywood.

 

It is looking pretty good, Mike.