How to build a greenhouse
Buying a greenhouse structure from a supplier, then assembling it yourself can save you more than £300 on construction costs – and the bigger the structure, the more you’ll save. On top of building costs, you’ll be saving on ground levelling, building foundations or laying paths inside. None of this is beyond the capabilties of a seasoned ‘do-it-yourselfer’, especially as all greenhouses come with full instructions.
The construction skills required are basic, but with good preparation you can avoid time-consuming pitfalls. This will mean you can assemble the structure and start growing as soon as possible.
First, get the site levelled and the foundations laid. If you’re on an exposed site, or simply wish to conceal the structure, it’s worth putting up fences or screens.
Once the greenhouse arrives, go through all the kit and check all the pieces are there. Read the instructions carefully, so you can visualise how the structure fits together. Be sure to enlist some helpers – two or three people are needed to assemble a greenhouse.
How to do it
Lay the base
Whether you’re using an existing foundation or building your own from concrete, brick or paving slabs, it needs to be level and square. Check it’s flat with a spirit level, and make sure the diagonals are the same length to keep it square (if it’s not in line, the glass panes won’t fit). When building a base, check the exact size of the frame before starting: although often described as 8x10ft or 6x8ft, these dimensions are approximate and frames are usually bigger.
Build the frame
It’s a good idea to put all the clips and bolts into separate pots before you start so you don’t lose them. Lay out the pieces of frame, assemble each section and attach together. Then carry the sections to your base and screw them in place. Fasten roof sections, roof bars and corner strengthening bars, but don’t over-tighten. at this stage, you’re just holding things together until you add the glass, at which point further adjustments may be needed.
Hang the door
Having assembled the door, you can fit the door runners when the rest of the frame is complete. Then slide the door onto the upper, then lower, tracks. Adjust the height of the top track until the door is running smoothly. If you have them, this is a good time to install automatic window openers and louvre vents. These help to keep an even temperature inside the greenhouse, avoiding spikes of heat in summer, which could scorch tender plants.
Fit the glass
Line the glazing bars with foam glazing tape or rubber strips. These will form a seal between the greenhouse frame and glass and help cushion the panes. you can use a pane to check your corners are square, and a spirit level to make sure everything is level. This will ensure the glass is securely and tightly supported. Glaze the roof first of all, while you can still move around freely inside and outside the structure. Once the roof is on, fix the wall panes.
Tighten it up
Tighten it up as you’re building, you need to keeping checking the bars with a spirit level. It is vital to keep the uprights and horizontals square or the glass won’t fit snugly. You may need to make minor adjustments as you proceed. Once you’ve fitted all the glazing, you can go round the again and tighten all the bolts. Take care not to over-tighten, as bolts can snap or you may even crack the glass. Once everything above ground is secure, you can finally tighten the base fittings.
Install the glass in one go. Don’t leave the greenhouse partially glazed over night – a strong gust of wind can break the fixed glazing panels and bend the frame.