How to Build a Greenhouse

Add another layer of 2-by-4s on top of the first layer, staggering the joints at the corners. Secure everything with screws, making sure the boards are square. Attach braces to hold the frame square while you’re working.

The base for our kit can be installed directly on the grass as long as the ground is level, but we chose to remove our grass and put down a gravel floor. Some codes might require paver base under the frame. 

To begin the gravel floor, use an edger to outline the frame to dig for the foundation. Set the frame aside and dig up the area. Then lay down some landscape fabric.

Pour the paver base, wet it and tamp it down. Get it as close to level as you can.

Set the wood base in position and check for level. If you’re adding permanent utilities to your greenhouse, now would be the time to run your lines.

Secure the greenhouse foundation. Our greenhouse kit includes anchors to hold it in place during strong winds, but for this project we installed longer shed anchors because we added a thick paver base. Use a long piece of rebar to create a pilot hole for the anchor. Attach a screw eye or eye-head lag screw rated for treated lumber to the frame. Use the rebar to help drive the anchor into the ground and then attach the anchor to the screw eye with the anchor kit's steel cable and clamp.

At this point, our local building inspector wanted to check the foundation before we attached the frame, so we paused construction. Your procedure may vary depending on local codes.

After our foundation passed inspection, we added some pea gravel inside the frame. It’s easier to add the floor for the greenhouse before the structure goes up.

Mark the outward-facing side on the polycarbonate panels. The panels will typically have a cover on them that helps identify which side has the UV protective coating. If you remove this coating prior to installation, you’ll need to know which is the exterior side.

It’s a good idea to assemble some of the smaller components of the greenhouse before building the metal greenhouse frame so they're ready to use when you need them. Link the framing members and secure them by inserting T-bolts into the channel and tightening the nuts. You can use the included wrench, a ratchet or a drill on a low torque, low speed setting.

Assemble the roof ridge pieces with the connectors and brackets.

For each door, assemble part of the frame and then slide the panel in place. Secure it with the other side of the frame and then attach the door stop.

For the aluminum base of the greenhouse, assemble the profile pieces on the wood and then connect them with the brackets. Double-check that everything is level, and secure the base to the wood frame with the screws.

Install the first framing member in the front corner. Hold it in place and then slide the panels into the channels for the side wall and the front wall. Hold everything together with the brackets, nuts and bolts. For the rest of the side wall, use the included spacing tool to get the correct position for the framing members and then secure them with the brackets. The panels slide into the channels. Secure the brackets to the outside as well. When you get to the back wall, put the first panel just around the corner for now.

The gutter goes on top of the side wall, but before installing it, trim a 1/4-inch-by-1/4-inch notch off the corner of the front and back panels using scissors or a utility knife.

Sit the gutter on top of the wall. You might need to tap it with a rubber mallet to make sure it's flush at the ends. Secure it to the walls with brackets and bolts.

Use the spacing tool and the brackets to set the back wall. Notice the taller framing members with the angled profile. Place these near the middle of the wall. Add the short, horizontal frame pieces at the top of the panels. Cross brackets will hold the back wall together. Next, assemble the other side wall. Secure the gutter on top.

On the front wall with the door, add the hinges to the frame. When you’re finished, they should be on the outside of the greenhouse. Then slide the framing members into position.

Next, hold the door framing together by the horizontal piece at the top of the panel and secure it with the brackets and bolts. Set the angled panels in place, then add the header piece and the barrel bolt lock.

Set the top panels in place and attach the corner brackets on the inside. You might have to trim the angled panels to make the framing fit on top. The gutters have a special bracket that covers the end and holds the corner of the structure together. On the back wall, attach the rest of the framing members, panels and brackets.

To secure the roof ridge, place the inside support brackets in position on the framing and then place the ridge. You might have to cut the tips of the angled panels to set the ridge in place. Then secure the roof ridge with bolts.

To give the ridge some extra support, install 2-inch-by-4-inch boards as braces underneath, just until the roof panels are installed. Clamps can help keep them secured.

Slide the panels under the ridge cap and rest them on the gutter. Place the framing member at the exposed edge and then secure it with the brackets and bolts. Now the roof panel will be secure.

Install the panels at both gable ends first, add the next panels toward the middle, then add the next set and finish out the rest of the full panels. Some spots will be skipped. These are for the roof vents, which rest on shorter panels near the bottom of the roof. (See the instructions for your greenhouse for exact positioning.) We loosened the bottom brackets to help slide the short roof panels into place.

When the panels are in place, add all of the support braces at the walls and under the ridge. Double-check the entire frame to make sure everything is straight and square, and then secure the end plate at the ridge.

Along the top of the gutter, add a bead of silicone sealant and the trim plate. Don’t forget to put the plugs in the gutters.

The roof vents on our greenhouse have automatic openers that release any excess heat that builds up when the temperature rises. The cylinders are filled with wax that expands in the heat to open up the vent.

For assembly, it’s helpful to store the openers in the freezer just to make them a little bit easier to work with. To install, mark the center on the inside of the roof vent panel. Then hold the opener in place and mark the screw holes. 

Drive the screws in and back them out. Secure the opener with the screws and on the outside, drive the screws through a gripping plate. It’s a good idea to cover the tips with screw caps. Check your kit to see if screw caps are included.

Lock the vent panel on the roof ridge. Now secure the other side of the opener to the stationary roof panel with screws and another gripping plate.

Attach the doors to the hinges with the screws. Make sure the barrel bolt works on the closed doors. Our kit includes self-closing doors and sealant tape to apply along the frame and the lower door. Attach the spring to the inside of the greenhouse with a T-bolt and to the door with a screw.

You’re now ready to add finishing touches and enjoy your new greenhouse.