Closing Everything In
While building your frame, you should have determined where your doors and windows will go. Keep in mind, the idea is to build simple greenhouse structures, so don’t get too carried away. The easiest option for doors is in the sidewalls. Otherwise, you will need to do some additional framing on either end of your greenhouse to accommodate doors there. If you have never framed a door in an open space like the ends of your greenhouse, you might want to save that lesson for a different project.
How you secure your windows and doors will depend on what type of material you are working with. Most windows and doors have framing intended for securing the unit to the wall framing. However, using reclaimed materials, you might have to get a little creative. This is where a little ingenuity, glue, screws, and caulking come into play. Your primary concern should be sturdy installation with a good seal. Doors and windows should open easily. Doors should be squared to maintain structural integrity.
Any areas not already covered by windows or doors require plastic sheeting. For the greenhouse ends, additional wood strips nailed across from one wall to the next will help secure plastic. Any seams in the plastic should overlap. For example, when closing in either short end of your greenhouse, the plastic should be stretched in one sheet from end to end. Wrap plastic ends around the first wall studs and staple on the inside of the greenhouse wall. When you start stretching the plastic over the long sidewalls, make sure it overlaps the plastic from the short sidewalls.
To reinforce the tops and bottoms of plastic sheets, wrap the plastic ends around wood lathe strips, then nail or screw strips to studs or the foundation. A dab of weather resistant glue around the nail or screw head will help prevent premature tearing. Where plastic meets window or door frames, you can also wrap the plastic end around lathe strips and nail in place. Seal the seam with a little caulking. If you truly want to build simple greenhouse options, you can always omit the windows and simply wrap the entire greenhouse (save the doors) in plastic. However, that means more work to set up ventilation for managing airflow and temperature.