How to build a greenhouse

dave kilvington
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How to build a greenhouse

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Project Overview

A movable greenhouse is a great idea for keen gardeners or vegetable growers. It gives your plants every chance to thrive by allowing you to follow the sun and avoid the harsh weather and insects that may affect their growth. We’ll show you how easy it is to build one.

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How to avoid hitting your thumb with a hammer

No matter how careful you are with a hammer, sometimes you hit your thumb, especially when it comes to small nails. An easy way to avoid this is by using a pair of pliers or a wooden peg to hold the nail in place while you hammer it in. Job done and no pain.

Step by Step Instructions

1 Pre-cut the timber to size
2 Make the floor frame
3 Attach the subfloor
4 Attach the caster wheels
5 Attach the flooring
6 Build the front frame
7 Measure for the studs
8 Secure the studs
9 Make the door
10 Build the back and side frames
11 Attach the plastic
12 Attach the hinges and bolt to the door
13 Attach the frames to the base
14 Attach the roof battens
15 Measure and mark for your polycarbonate
16 Cut the polycarbonate roof
17 Attach the roof
18 Position and fill your greenhouse
  • Step 1. Pre-cut the timber to size

    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)

  • Step 2. Make the floor frame

    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.

  • Step 3. Attach the subfloor

    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.

  • Step 4. Attach the caster wheels

    Turn the frame over. Use the 125mm bugle screws to attach the caster wheels in each corner of the frame. There’s no need to pre-drill, just screw them straight in. A good tip is to put the two casters with stoppers on diagonal corners.
  • Step 5. Attach the flooring

    Secure the first piece of timber flooring rib side down and flush with the edge. Then use a timber offcut as a spacer and lay the next length down. Secure it with the fixing gun, and repeat this process until you’ve finished the floor. These gaps in the floor will help you with drainage.
  • Step 6. Build the front frame

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

  • Step 7. Measure for the studs

    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.

  • Step 8. Secure the studs

    Use the fixing gun to secure the three studs.

  • Step 9. Make the door

    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.

  • Step 10. Build the back and side frames

    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.

  • Step 11. Attach the plastic

    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.

  • Step 12. Attach the hinges and bolt to the door

    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. 

  • Step 13. Attach the frames to the base

    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.

     

  • Step 14. Attach the roof battens

    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.

  • Step 15. Measure and mark for your polycarbonate

    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.

  • Step 16. Cut the polycarbonate roof

    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.

  • Step 17. Attach the roof

    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. 

  • Step 18. Position and fill your greenhouse

    Now all you have to do is roll your greenery into the right location and fill it with your favourite plants.
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