Rebuilding our Greenhouse

The rebuilt greenhouse will remain 12 feet 4 inches north to south, as defined by the existing concrete base. It will be divided into a "shed end", two short stories (14 feet to the tops of the V roof), 14 feet of the west end, and a 30 foot cylindrical greenhouse on the west end, 10 feet high. The greenhouse will retain the metal bracing of the old wooden greenhouse, shifted upwards to support PVC pipe hoops spaced 23 inches apart. The hoops will support overlapping 49 inch strips of Solexx double wall polycarbonate plastic, sealed with caulk and attached with self-tapping screws. The lower south edge of the greenhouse will be a continuous strip vent inlet. The back side of the greenhouse faces the northern neighbor's fence and will not have much insolation or direct wind loading.

The east end of the greenhouse is 5 feet from another shed to the east, and a healthy 125 foot Douglas fir east of that. The east edge of the property is 160 feet east of the east end of the greenhouse. It is "landlocked" and inaccessable for flag development. The gravel drive south of the main house is big enough to back in delivery trucks with care, but not firetrucks, and not wide enough for a 15 foot development easement.

The "shed"

The interface between shed and greenhouse is a tall prism opening, 8 feet wide and 9.5 feet tall in the center, with the east end of the shed a timber box around an 18 inch wide air channel up to slow fans in the upper story. Greenhouses should have 1 air change per 90 seconds in peak growing season; 2000 cfm for the two large slow fans, an air speed of 3 feet per second, 2 miles per hour. The open channel will contain structural members connecting the north and south of the building, along with two plywood diaphragms. Unlike the rotted greenhouse shed this replaces, the northeast and southeast "pillars" will be wide enough to take significant bending moment.

The shed will have an inverted V roof covered with Snap-Loc standing seam metal, intended to capture rain water down an inside central gutter tilted towards the east. The gutter can be cleaned from inside the building. The V roof will not shed snow like a traditional gabled roof, so it must be stronger. It must be modelled for larger lift forces pushing up the eaves, as well as Bernoulli lift above. However, a V roof is safer to work on, especially in high wind conditions. Pitch will be 3.5 in 12, so the height of the triangles formed will be 21.5 inches higher on north and south sides than in the center trough.

The shed will be just tall enough to accomodate a half floor 62 inches above the greenhouse floor along the north side, and 84 inches high on the south side. Low headroom. The spaces on top and bottom will store garden equipment; paint and fuel and hazardous chemicals, as well as a gas riding mower for the half-acre back yard, go in the separate shed to the east. The north floor will be reconfigurable to hold an electric wheelchair lift, should one prove necessary a decade or two from now.

Doorways will be 36 inches wide. The shed will have electricity (30A 2 phase), and high efficiency electronic ballast fluorescent lights, perhaps DALI controlled. Mostly, light will come from three south-facing windows, 18 inches wide between studs, and through the large opening to the greenhouse. A capped-off city gas pipe, and a pipe that used to connect to a propane tank, enter the existing shed. The concrete base is plumbed; the existing taps will be replaced with double hose bibs, and insulated doors along the base of the greenhouse will allow outside hoses to connect to those bibs. We may also add valves to deliver water to future raised beds, and a small orchard on the eastern half of the back yard (I want to eliminate that riding mower!).