How to build a greenhouse

To make this project easier, you can get all of your timber pre-cut at your local Bunnings. A good tip is to group and label the timber lengths together for each side so you know where it will be used. You can make your greenhouse any size you like, here's the cutting list we used:

200mm x 50mm pine:

• 1500mm x 2
• 1200mm x 2

70mm x 35mm pine:

• 1600mm x 7
• 1500mm x 2
• 1200mm x 6
• 1150mm x 11
• 1140mm x 2
• 1070mm x 1
• 670mm x 1
• 315mm x 3
• 1030mm x 4

1500mm x 90mm treated pine decking boards x 9 (floorboards)

1600mm x 70mm x 45mm treated pine x 1 (roof batten)

1600mm x 70mm x 35mm treated pine x 1 (roof batten)

1600mm x 50mm x 25mm rough header x 1 (roof batten)

Take the four 1600mm x 1200mm hardwood sleepers and make a rectangle with them. Make sure the edges are flush and then pre-drill holes with the 5mm drill bit. Fix the frame together with 125mm bugle screws.

Place the 1500mm x 50mm x 2 lengths and 1200mm x 50mm x 2 lengths for the subfloor on the inside of the floor frame. Then attach them to the floor frame with the fixing gun. You should also add two joists an equal distance apart and use the nail gun to secure them down for extra support.

Make a rectangular frame with the 2 x 1600mm lengths and 2 x 1150mm lengths of timber. Join them together with the framing gun. 

Once you've worked out how big you want the greenhouse door to be, measure and mark where the studs will go. Remember to take into account the width of the third stud to attach the door hinge to.

Use the fixing gun to secure the three studs.

Lay out the frame for the door with the 2 x 670mm lengths, 2 x 1140mm lengths, 1 x 1070mm length for the centre and 3 x 315mm lengths for the noggins. Before fixing with a framing gun, be sure the timber is flush to the frame.

Now it's time to repeat the previous steps to build the back and side frames for the greenhouse. Note that you won't have to include the door in the frames.

Now that you've made your frames it's time to wrap them in plastic. Make the plastic as tight as possible and fix with a hammer and the foil fixers. Trim any excess plastic with a utility knife. A good tip is to attach the fixers to the inside of the frame so that the finished greenhouse looks neat. You'll need to repeat this process for each of the four frames.

Screw the hinges into the side studs. You'll find the screws for this in the pack with the 200mm hinges. Then attach the bolt. Screw the bracket into the noggin and the pad bolt to the door. 

You'll need someone to help you with this step. Attach the sides, back and front to the base frame and to each other using the 125mm bugle screws. Make sure all of the frames are flush with the edges of the base and the other frames before securing.

You'll need a slight fall on the roof, so attach the timber battens with different widths in descending order. Starting at the front, secure the 70mm x 45mm x 1600mm batten, then the 70mm x 35mm x 1600mm batten and then the 50mm x 25mm rough header.

Measure the length of the roof for the greenhouse. Allow a little extra overhang at the front and back for runoff. Transfer these measurements onto the polycarbonate. Mark the line with masking tape because this helps ensure a clean, straight cut.

Clamp the polycarbonate to the top of the greenhouse to make sure it doesn't move so you get a smooth, straight cut. When cutting, use the jigsaw with a metal blade on the medium setting, and don't forget to wear the appropriate safety gear when cutting.

Attach the polycarbonate roofing to the greenhouse using roof screws. You should screw them into every second crest of the corrugate for a secure roof.