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How to Build a Greenhouse from a Kit

A greenhouse is a wonderful addition to any garden. To save money, consider assembling your own from a kit.

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Step 1: Prepare the Base

For the best results, place the greenhouse so that the long side faces south and gets at least six hours of sunlight. Dig a trench the same size as the perimeter of the greenhouse 6" deep to accommodate the 4” x 6” timbers. Fill the trench with crushed limestone and tamp it down. Cut the timbers to length and put them on top of the aggregate around the perimeter of the base. Make sure timbers are level. Square the timbers by measuring corner to corner and then anchor them in with rebar. Pre-drill holes in the ends of the timbers and secure with 12" spikes.

preparing base for greenhouse

Step 2: Lay the Paver Floor

Remove all the grass inside of the timbers, leveling the ground as you go. Lay the paver blocks flush with the top of the base of the timbers. Cut any off-sized pavers with a splitter. Dump sand over the floor and sweep it into the cracks.

lay paver floor

Step 3: Assemble the End Walls

Working from the inside of the greenhouse, attach the bottom plate to the corner struts and the wall struts to the bottom plate. The corner struts attach to the roof gable with a corner plate. Use two bolts in the corner wall struts and two in the roof gable. Put two additional bolts in the center wall struts. These will be used to connect the braces and door header. Slide on four bolts for the roof gable and attach them to the corner strut with an angle plate and then tighten the nuts. Tighten the bolts enough to hold them in place. Assemble the other end wall in the same manner but without a door frame.

corner struts attach to roof gable at corner plate

Step 4: Assemble the Side Walls

Lay out the wall struts and attach to the bottom sill of the greenhouse. The two side walls are assembled in the same manner.

Step 5: Raise the Walls

The end wall pieces have a channel, and this is where the side wall slides in. To attach the corners, loosen the four nuts on the plate that connects the end wall to the roof gable. Spread this connection apart in order to slide in the side-wall section, then bolt the bottom braces together. Do this in each of the four corners.

spread connection apart to slide in wall section

Step 6: Attach the Ridge Pole and Struts

To attach the ridge pole, which runs from end gable to end gable, just loosen the bracket, slide it in and tighten it up. Attach the six roof struts by lining them up with the wall struts and bolting them in.

attach ridge pole and struts

Step 7: Assemble the Door and Window Frames

Assemble the frames for the doors and windows and secure them with screws. Attach the lock and handle to the door.

assemble frames for doors and windows

Step 8: Install the Window and Door Panes

Slide the gaskets on the top and bottom of the polycarbonate panels before applying the silicone. Run short beads of silicone along the edge of the frame, install the frame and secure it with the provided spring clips. Once a panel is in place, there is another vinyl gasket that goes along the side of each panel. Snap it into place between the frame and the polycarbonate.

install the window and door panes

Step 9: Secure the Greenhouse to the Base

Make sure the greenhouse frame is sitting squarely and evenly on the base before screwing it down. To fasten, pre-drill and then drive deck screws through the bottom sill of the greenhouse into the timber.

fasten, pre drill and drive screws through sill

Step 10: Install the Final Panes

Slip the panels into place and measure the gaskets to the proper length. Press the gasket all the way down and into place. Bow and flex the side-wall panels into place. After the side walls are in, press side gaskets into place. With the side panels and gaskets in, it's time to put one roof panel in place and then slide the strut down on top of it. The windows should just slide into place.

bow and flex side wall panels into place

Step 11: Attach Door and Downspout

Attach the hinges to the door frame and then slide the door into place. The top of the greenhouse wall is the gutter system. To have the water drain away from the greenhouse, install the included downspout.

have water drain away from greenhouse

Step 12: Install an Optional Exhaust Fan

Use a utility knife to cut a hole in the polycarbonate panel on the back wall of the greenhouse. Install the louver on the outside of the greenhouse. Mount the fan with the motor on the inside using carriage bolts.

install louver on outside of greenhouse

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