How to build a polytunnel

You will need

Polytunnel kit from supplier

Cement for foundation tubes, if required

Hammers

Wooden block

Adjustable spanners

Screwdrivers

Spirit level

Anti-hot spot tape

Do it: all year round
Takes just: a weekend

Overview

Building your own polytunnel from a kit can save you hundreds of pounds in construction costs. All you need are some basic DIY skills and some willing helpers - four people is ideal.

Before assembling your kit, ensure the site is level. If your site is exposed, you might wish to put up fences, screens or even hedging. When the kit arrives, check thoroughly that all components are there, and read the instructions carefully.

Once the structure is up, add a path, if necessary, using paving slabs, bricks, or self-setting gravel edged with timber. Where you intend to plant direct into the border soil, fork it thoroughly to relieve any compaction and incorporate plenty of compost. Alternatively, if you'll be growing in pots and growing bags, or on benches, firm the soil, cover with black polythene or weed-suppressing fabric and top off with gravel to create a hard-standing area.


How to do it

Installing polytunnel foundations

Install foundations

1

Correctly placed foundation tubes will ensure the stability of your polytunnel. Use an anchor plate with the tubes (shown above) if fitting a base rail – see step 3 – or on exposed windy sites. You can also cement in your foundation tubes. Mark the base positions, making sure they are evenly-spaced and check all the angles are square. Then drive the foundation tubes into the ground, hammering onto a wooden block to avoid damaging them.


Building a polytunnel frame

Build the frame

Connect the separate hoop sections together, then slide the ends over the foundation tubes. Fix the support struts to each hoop. always check the positioning of bolts and other fittings before you attach them, making sure they won’t rub against the cover and cause it to tear. Finally, fit the ridge pole, corner bracing and door frames. Check that the hoops are all straight and in line, then tighten all the joints carefully.

Adding a polytunnel base rail

Add a base rail

There are two ways to hold the plastic cover in place: pinning it to a wooden base rail which is fitted to the foundation tubes; or burying a skirt of polythene in a trench 30cm deep. A base rail is the easiest way, particularly if there’s not enough space around the polytunnel to dig out a trench. If your model is supplied without a base rail, you can make one using lengths of 70 x 45mm timber, cut to length, then bolted on to the foundation tubes.

Polytunnel covering

Cover the frame

You can buy anti-hot spot tape from most polytunnel/greenhouse suppliers. Place a strip along each hoop to cushion the polythene and protect it from friction and heat – it should increase the life of the cover by up to a year. Clear any stones from the ground and unroll the cover, sliding it over the hoops so it sits evenly over the frame. Fix it to the base rail or bury in a trench. Keep the plastic taut when fitting. Cut it to fit the doors by making a v-shaped flap.

Attaching polytunnel doors

Attach the doors

Just in case the wind picks up overnight, it’s best to fit the doors on the same day as the cover. start by making the frames for all the doors and covering them with polythene. sliding doors hang from a runner attached to the top of the door frame, while hinged types are designed to swing on one side of the frame. Hold the door in the frame before attaching it, to make sure that you hang it squarely in place so it fits the opening correctly.

Adam's tip

Choose a warm day to install the cover. Warm weather makes the plastic more pliable and therefore easier to stretch tightly over the frame.




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