How to Build a Lean-To Style Greenhouse

Place four concrete blocks at corners of the greenhouse location, making a 6 x 12 foot rectangle. Place the remaining blocks four feet apart between two outside corners. Dig holes for the foundation piers and insert the blocks into the holes, leaving their tops two inches above ground. Measure and cut 2 x 4 boards for sills to tie the blocks together along the three outside walls.

Attach a ledger board to the house. Position the bottom of the 2 x 6 board along a line eight feet above ground level; fasten to the house with lag screws in every other stud. Tuck flashing under the house siding and over the ledger to create a waterproof joint between the house and ledger.

Cut 14 2 x 4 boards 5 feet 9 inches long for studs.

Cut two 2 x 4 boards 12 feet long for the outside top and bottom plates---the boards which will hold the studs. Cut four 2 x 4 boards 7 feet 8½ inches long for the side plates.

Place the outside top and bottom plates flat on the ground, next to each other. Use the framing square to mark stud centers every two feet on the plates and mark the sides of each stud.

Assemble the front wall framing by laying the plates and studs into place on the ground. Line up each stud with the markings; nail plates onto them. The on-center distance between the first and second stud will be only 23¼ inches, to allow for an extra overlapping ridge on the plastic panels.

Place the wall frame on the foundation; nail into place. Use the level to ensure the studs are level.

Repeat steps 5 to 7 to frame the side wall without the door.

For side wall with door, measure stud locations, but leave a 2-foot 6¼-inch space in the center for the door. Place two studs on each side of the door, 6 inches to 1 foot apart. Cut two cross-braces and nail them between the door studs for stabilization when shutting the door. Prepare the frame for the door 5 feet 9 inches high and 2½ feet wide. Complete the side wall as for the other walls.

Prepare roof rafters. Place a 2 x 4 board over the ledger board and the front wall; mark cutting locations for board to fit in the joist hanger and angle to the front wall. Cut the board according to measurements; check for correct fit. Use the cut board as a template for eight more rafters. Place the rafters into place, two at each end of the roof and one over each wall stud. Cut short lengths of 2 x 4 to cross-brace the rafters and fill in between the rafters and top plates on the side walls.

Position and attach the vents in desired locations on the roof or side walls.

Nail molding across top and bottom of ledger board to prevent drafts. Place half-round molding strips along each rafter to support the plastic panels. Apply a thin layer of sealant to the top of molding if using rubber or redwood molding.

Pre-drill holes in the plastic panels. Using screw nails---with waterproofing grommets and screw threads attached---position and attach the plastic panels onto the greenhouse. On the roof, nail panels to rafters and cross-braces every 12 inches or three ridges. Leave a 2-inch overhang in front to prevent drips and place panels flush around the vents. On the front, nail into every ridge for additional protection against wind damage. Place sealant over the joints; cover with lats---or thin strips of wood.

Cover door framing with a plastic panel. Attach the door into place with hinges and the latch.