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.