David Domoney Explains How to DIY install a Keder Greenhouse

If you’ve ever dreamt of growing your own veg year-round, the right growing space makes a massive difference. The Keder greenhouse provides this in spades, offering the flexibility of a polytunnel and the stability of a traditional greenhouse.

The great news? You can build one yourself.

Tools you will need

Before you get started, make sure you have the right tools to hand. Here’s what you’ll need:

·      Tape measure and spirit level

·      Stanley knife and wood saw

·      Sledgehammer and claw hammer

·      Two 13mm spanners

·      Cordless drill with torque control

·      8mm drill bit

·      5mm Allen key (for the framework)

·      Stepladder (lightweight but sturdy)

·      Heavy-duty staple gun (with plenty of staples)

·      8mm hexagonal socket (provided with kit)

These tools make the job easier and help ensure a safe and secure installation. The greenhouse also comes with a detailed instruction manual and a video guide. This makes the installation process much easier to visualise and follow step-by-step.

Why choose a Keder Greenhouse?

For UK gardeners seeking an all-weather greenhouse that doesn’t quit, the Keder ticks every box. It looks smart, but it’s the build quality that stands out. The high-tensile steel frame gave me instant confidence that this structure was built to last. And what truly sets it apart is the durable nine-layer bubble cladding. Come wind, rain or snow, your Keder greenhouse will stand resolute.

Once I had my Keder greenhouse up, I was taken aback by its sturdiness. In the time since installation, mine has endured strong winds and heavy rain, whilst the interior stayed light, bright, and maintained temperatures skilfully.

The nine-layer Keder cladding is clever too. With a thermal R-value of 1.7, it maintains steady temperatures, which tender seedlings need to thrive. Since installing mine, I’ve worried far less about cold snaps or sudden heat.

You can also add roof vents, staging, crop rails, and bracing kits to customise your setup. With proper ventilation and a strong frame, it’s a greenhouse for all seasons.

Step 1 – Choose the Right Spot

Select a flat, clear area. The ground should be level to within 25cm over the full width and length.

Allow at least one metre of space around all sides for access. Position the greenhouse so one long side faces the prevailing wind, typically south-west in the UK.

Choosing the right spot is important, but remember, the nine-layer cladding does a lot of work to guarantee the lighting is just right. Its ability to distribute light means you don’t get harsh shadows or hotspots, just soft, even light reaching all your plants.

Step 2 – Build the Base

This stage is crucial. A strong base and sturdy framework mean your Keder can handle winds up to 120mph. That’s serious weatherproofing, ideal for even blustery hillside sites.

Lay out the brown base timbers into a rectangle. The rebated ends of the shorter timbers should fit squarely against the longer sides. Attach the metal corner brackets and stub brackets using a drill and wood screws.

Secure each base corner with a ground anchor. Hammer it in at a 22° angle, leaving just three inches visible above ground. In exposed areas, consider setting these into concrete for extra strength.

Step 3 – Build a Windproof, Steel-Strong Frame

Each hoop is made from two side tubes, one top tube, and two joiners. Slide the side tubes onto the stub brackets.

Next, fit two O-ring brackets to each side tube—one 6 inches and one 32 inches from the base. These hold your braces and ridge bars later.

Insert a joiner into each side tube and connect the top tube to form a hoop. Repeat for all hoops, spacing them exactly two metres apart.

If your greenhouse is longer than 2m, add centre hoops accordingly. Use a spirit level to ensure everything is upright before tightening bolts.

If you ordered an extreme bracing kit, auto roof vent, or staging, add extra O-rings as instructed in the manual. If you have both the extreme bracing kit and auto roof vent, these O-rings are on the centre hoop side tube and the end hoop side tube.

Fit roof vent brackets now if needed.

Step 4 – Add Ridge and Bracing Bars

With hoops in place, connect the top O-rings with ridge bars to form the roof spine. Use the 32-inch-high O-rings for the side ridge bars.

Slide the ridge bar tensioners into each bar, but don’t fix them yet. Final tightening happens during cladding.

If you have a bracing kit, fit extra bars 10 inches below the top of each hoop. These braces stiffen the frame and provide a place to mount staging or shelves.

Your greenhouse will now take on its full shape.

Step 5 – Fit the Roof Vent, Rear Vent and Door (if included)

Roof vent

Decide where to place your roof vent—ideally away from strong winds. Slide the roof vent bar brackets onto two side hoops, two inches from the top. Make sure they face each other and inwards.

Add roof vent hinges to the top tubes, four inches from each end. Fit the roof vent bar between the brackets, then attach the vent frame to the hinges. It should sit flush with the bar below.

Tape it temporarily in place to stop it swinging until the cladding is complete.

Rear Vent

Assemble the rear vent frame, posts, lintel, and sill on the ground, leaving small gaps (1/4 inch) around the vent. Secure parts with joiner plates and stop plates.

Lift the full frame into place at the rear. Align it with the hoop and base, then fix using lintel brackets. Check everything is square before securing fully.

Fitting the door

Build the door frame flat on the ground. Fix one post flush to the frame and leave a ¼ inch gap on the other side. Attach the lintel across the top.

Stand the frame upright and slot it into position at the front of the greenhouse. Use brackets and joiner plates to fix it to the hoop and base. The door itself is completed after cladding.

Step 6 – Clad the Ends with Keder Plastic

Unroll the end panels and separate them. The thicker, smoother side should face outwards to reflect light and repel rain.

Drape the sheet across the end frame, covering the lintel and base. Then staple it every 10–15cm across the lintel.

Trim the excess with a Stanley knife, leaving a 15cm flap all around. This flap helps with weatherproofing. Then, use the noggin provided to pull the plastic tight.

Clamp the plastic to the hoops using profile strips and screws. Begin 90cm above ground and work upwards and over the arch for best tension.

Now, use the profile strips and roughly lay them over each hoop section. The smaller groove should face away from the greenhouse. Cut a ‘V’ into the end of each strip to make feeding the cladding through easier. Just ensure the edges aren’t left sharp.

Step 7 – Clad the Roof and Sides

If you have roof vents, take extra care during cladding. Spray silicone into the profile channels to make feeding the Keder easier.

Insert the Keder beading into the profile and slide it evenly over the hoop. Work in pairs if possible; one feeding, one pulling.

For the standard sections, repeat this method. Always start on the sheltered side to avoid the wind catching loose plastic. Pull the Keder tight as you go.

Leave around 25cm overhang at each end. This will be tensioned in the next step.

Step 8 – Tension the Keder Cladding

Inside the greenhouse, wedge a 2m wooden batten between the hoops to force them gently apart. This creates even horizontal tension.

Secure ridge and side braces to their tensioners with self-tapping screws. Adjust slightly if needed to get a snug fit.

For vertical tensioning, stand on the base flap to pull the cladding down tight. Staple at 5cm intervals for a firm hold.

Cover all staples with timber battens and fix them in place using galvanised nails. This not only looks tidy but also helps shed water efficiently.

Step 9 – Add Finishing Touches

Attach battens over any staples, install handles and catches, and ensure the door opens freely.

If you’ve included staging, secure the slats to the frame on the cross supports, and make sure they’re level with a spirit level.

Crop rails can also be added, by pushing the ends onto the connectors, and screwed into place.

Install your vent chains to prevent damage in strong winds. A roof vent lock is available for extra security in high-wind locations.

Finally, screw on the nameplate, and your Keder greenhouse is ready!

 A DIY Keder greenhouse isn’t just a great weekend project. It’s an investment in your gardening future. You’ll enjoy lush, healthy crops, longer seasons and pride in knowing you built it yourself.

By following the steps carefully, you’ll have a space that’s practical, productive, and ready for anything the weather throws at it.

David Domoney

To find out more about our Brand Ambassador and Guest Blog Writer visit https://www.kederdomestic.co.uk/david-domoney

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