When building the foundation, if there is a door in the greenhouse wall, leave a 2″ plus or minus drop in the footing for the door buck spreader. (if this was not done, reduce the length off each door buck, if necessary, by cutting the excess material off the top, at the same angle as the factory cut.)
The normal wall height can be raised or lowered to suit local conditions. If the wall is raised, increase the height of the door “sill” an equal amount, and build a sloping ramp or steps as needed. Or, order longer door buck extrusions, and fabricate to fit during construction. If the wall height is lowered, build an excavated areaway for the door or, raise the door and frame and cut the glass lite over the door to fit. The door can be raised as much a 9″ for lean-tos, 16″ for even span “O” models; 19″ for lean-tos, 21″ for even span Imperial models. Then, remove soil inside greenhouse to provide headroom.
For a greenhouse attached to another building, determine the furthest projection on building face in area where greenhouse is connected, and drop a plumb-bob to establish a starting point for construction of masonry footing.
Your greenhouse may be erected on hollow concrete or cinder block, poured concrete or brick foundation. The foundation should always rest on solid ground, with footings below frost level, approximately 36" deep. This is usually the required depth in most areas but will vary depending upon your location.
If a greenhouse is to be erected on the roof of a building, a watertight floor is required; see details. For supplemental greenhouse ventilation you can readily install standard basement sash in the masonry wall. Sash of this type in steel, wood or aluminum is available through your local building supply dealers.
In warm weather, the wall sash and roof vents can be opened and steady extra ventilation will result because of the flue effect provided.
If a Gas Heater is to be installed, leave an opening in the masonry wall, preferably in a gable end, according to heater instructions.
If a greenhouse cooler is planned, provide the necessary duct opening while building the wall; wall sash are not required when a Cooler is used.