Polycarbonate

We decided to use a three ply polycarbonate for our glazing. Again, decisions for a greenhouse are always weighing pros and cons of different options.
We liked how polycarbonate diffused sunlight, eliminating shadows and giving the plants a softer light. It is also a very durable product with a lifespan that could easily span decades. We also liked the option of using three or more ply glazing for the insulating value. Choosing the number of plies for a polycarbonate is another example of weighing advantages. The fewer plies the less sun gets into the greenhouse, but the greater the insulating value. Observation of our sight told us that it was a very sunny, hot location. So it made sense to use more plies which would reduce the intensity of the sun and give us more insulation on cold, winter nights. We chose a three ply. We attached the polycarbonate using screws with rubber washers that we bought at, you guessed it, Home Depot! We used tin to create a weatherproof junction between the 20 degree and 60 degree portions of the greenhouse. We used aluminum tape to seal the ends of the polycarbonate to keep moisture and dirt out of the cells. We thought this tape looked OK on the roofs, but did not like its look on the side walls. But it would be hidden by redwood trim around the doors and windows and along the edges of the greenhouse.

Side Walls

We framed the side walls to fit the rafters. The greenhouse would have a 32 inch screen door at each end for easy access from either side. The west end of the greenhouse would have a 4 foot by four foot window. We chose a “High E” window for the west side. High E windows let in less light, which is ideal for the west end since the late afternoon sun can overheat greenhouses. High E also has a higher insulating factor, which we liked as well. The east wall had two two foot by four foot windows. We chose “Low E” windows for the East wall to let in more of the morning light, when a greenhouse is cool and could use the heat.

60 Degree Portion Rafters

We ran the front, or 60 degree rafters from the sill plate to the center beam. We laid this portion on four foot centers, since it would not have much of a snow load at a 60 degree angle and to minimize shadows from the rafters. We also used redwood 2x6's for this.

Roof Rafters

We attached the greenhouse rafters to the garage rafters, following the same layout, which was on two foot centers. We attached a ledger beneath the greenhouse rafters for added support. The greenhouse rafters ran from the garage to the main beam of the greenhouse at a 20 degree angle, which was the same angle of the garage roof. We used redwood 2x6's for these rafters, most of which were reclaimed from a old deck. From observations and from figuring sun angles at different times of the year, we decided to cover the first two feet of the roof, closest to the garage with roofing instead of polycarbonate. This would offer some shading from the hot summer sun while allowing a maximum of the winder sun. These two feet could also be insulated for added efficiency.

Now the fun begins: Framing!

Digging was done. The cement was mixed and poured. We were done with the ditch witch, done insulating the footer. It was finally time to move above ground. Framing the greenhouse loomed ahead of us like a walk in the park, or perhaps a walk in the garden.

We wanted part of the south facing glazing to be at 60 degrees, which is perpendicular to the sun on December 21^st, and the other part to be at 30 degrees, which is perpendicular to the sun on June 21^st. These angles are ideal for growing plants.

A beam was needed to run the length of the greenhouse at that point. This proved to be tricky to set in exactly the right place, while tying it into the garage roof. The garage roof proved to be at 20 degrees. We decided to continue that angle down to the point where the 60 degree portion connected to it.

A post was also needed halfway to support the two 11 foot 2x10 beams. This post would end up being in the front raised bed, so we made the bottom portion a cement column that would not rot over time.

The beam was finally set at the exact right distance from the garage, so that the angle of the garage roof tied perfectly to it, as darkness fell onto our project. It was a good feeling of a job well done.

The Sill Plate

The sill plate is the means to connect the wooden framing to the cement stem wall. Place J bolts about every two feet in the cement at the top of the stem wall while it is still wet. After the cement dries attach a redwood or a treated 2x8 or 2x6 to the stem wall, depending on the size of the studs on your walls, with appropriate nuts and washers. We used a 2x8 green board since we have 2x6 redwood walls.

The Stem Wall

We chose not to use foam forms for creating the stemwall, both because of price and because having foam on both sides of the concrete negated it's mass inside the greenhouse. Instead, we rented plywood forms to pour the cement into, which we removed after the cement hardened. We then placed 1 1/2 " rigid insulation around the exterior.
We also chose to have the stemwall extend six inches above the planned 2 1/2 ft planting beds. Since ground level in the greenhouse was even with the bottom of the 7" footer, the stemwall ended up being 29" high. It is 8" thick. We ran 2- half inch horizontal pieces of rebar inside the wall attached to the 1/2 " uprights that were embedded in the footer, this is according to code. Aferward, we found that we liked the feel of standing 2 ft. below ground level in the greenhouse with the substantial stemwall surrounding us.

Naming Our Business

We have been fervently attempting to come up the the perfect business name that conveys what we want it to, yet is somewhat original and resonates with both of us.
What do you think of "Two Dorks and a Shovel?"

Underneath it All

Traditional greenhouses can overheat when the sun is out and freeze in it's absence. Typically, electrical or gas heating and cooling systems are installed to counteract adverse conditions. Our goal is a passive solar greenhouse, meaning it is "off the grid".
Our subterranean heating and cooling system uses the ground of the greenhouse as mass and a solar operated fan to help moderate the temperatures by pushing air slowly through the 4" perforated pipes. This system has the added benefit of keeping the roots of the plants warm and moist because it runs under the planting beds.


This is the Plenum, home-made made from a used hard plastic drum. It is a separate space compartment for air circulation. (heating, ventilation, cooling). The fan goes inside here.

Compost to the Rescue!

Plants in aged compost (left) Newly started compost is cooking (right)

So this is what you might call a "duh" moment. A while back I ran out of room to plant the rest of the tomato and pepper plants that I had started from seed back in the day. Worse, they have been residing in undersized containers. So today as I was checking in on the status of my compost which has been cooking for two years now and is about done, it occured to me that since it is just....there, waiting for the greenhouse to finish, why don't I plant the plants in it. Eureka. I will report back in a couple of weeks as to their condition.

Ditch Witch

No, this is not ditch (the) witch, something Erik has thought of a time or two.
This is the machine we used to dig 3 rows of 1 Ft deep x 7" wide trenches lengthwise along the floor of the greenhouse. This is where the drainpipe will go for the subterranean heating and cooling system which will be discussed in greater detail soon.

Home Sweet Home (Depot)

Our home away from home. We trip down there at LEAST twice a weekend. We might be needing to join some kind of 12-step program for this habit of ours. Just say no. Live in the moment, breath just breath and count to ten.

Winter Coat

Insulating the perimeter of the foundation is a step easily skipped. It is a giant pain to dig down another two feet and who would know? But it is essential. The greenhouse will not perform properly without it.

Cementing Our Future

Erik's son, Jordan became a welcome addition to the crew. Mixing the cement for the footer ourselves was a different experience than having a cement truck dump four or five yards into the footer forms. We Schlepped four tons of cement from the truck to the yard and into the mixer.
Mixing. Pouring the mixture one wheelbarrel at a time into the forms. Both Deb and Jordan turned out to have a knack for mixing and Erik for schlepping.