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Alan's Polytunnel
Alan P explains how to build a Poly-Tunnel
By: Clive B 
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A polytunnel using the following materials can be made to any size within reason, the smallest on our allotments is 8ft x 6ft and the largest is 14ft x 40ft. A polytunnel built as described below will stand up to storm force winds that would reduce a greenhouse to a heap of rubbish. Most materials can be begged or bought cheaply. The most costly item is the cover £86 for the one to cover my 10ft x 20ft tunnel (see photo on left) but, they have a guarantee of 5years and will last for 7 or 8 years. Tghe Scaffolding boards shown in the photo where used mainly because the site is on an incline and they were needed to hold the soil out on one side and in on the other, but they do help to protect the cover from accidental damage from spades and forks while gardening inside the tunnel.
Scaffolding tubes 48mm OD 5ft long tubes will give you about a 3ft straight-sided tunnel. 2 are required for every 5ft length of tunnel. Example…..a 15ft long tunnel will require 8. Source. Building sites, scrap metal merchants, derelict allotments or scaffolding firms where the will cut you some bent or damaged pipes for the price of a few pints if you ask nicely Tubing Mains gas (yellow) or mains water pipe (blue) 50mm ID. A 19ft length will span a 10ft wide tunnel giving a height at apex of about 8ft. Example a 15ft x 10ft tunnel will require 4off 19ft lengths of pipe Source. Large industrial building sites, new housing estates, council building yards where there will often be pieces left from a roll after jobs have been completed. Cost is usually nothing as they are glad to get rid of it. Alternatively, if a few people are building a tunnel a roll could be bought and shared. It does not cost a great deal, so I am told. Timber 8off 10ft lengths of 50mm x 50mm rough sawn timber to make the two frames and door Source Builders merchants about £2.50 a length Timber 50mm x 25mm slate battens, about ten are required for a 20ft tunnel. These are required for the stiffeners between tubes, to hold the cover to the frames and to make removable vents for the door and end frame. Source. Builders merchants. Cost about £1.50 for a 5m length Optional Old scaffolding boards or old floorboards. Enough to go round the perimeter of the tunnel Source. Scaffolding firms or reclamation sites. Cost….. depends how charming you are. Wood screws (6mm x 25mm roofing bolts optional) A trade pack of wood screws from ScewFix for about £6 will cover all requirements, roofing bolts can be purchased from there as well. Polytunnel cover Measure over the hoop plus two metres that are buried in the trench x the length of the tunnel plus the height at both ends. Covers are cut by the running metre from set widths …..7.2m…9.2m…11.2 Source Mail order

Knock the first tube into the ground so that it will stay upright, measure in 5ft increments to the furthest tube and knock this one in. Put a tight string line between these two tubes about 2 inches from the bottom. Knock the other tubes in using the string line at 5ft intervals.
Making a large square from three of the slate battens (using the 3,4,5 rule) and working at one end, temporarily position the first tube of the other side. Go to the other end and do the same again. (Check the distance between these two tubes is the same as the other side and then drive them in) Put the string line between these two tubes and knock the other tubes in at 5ft intervals. Now check by eye and measuring corner to corner that the tubes are square. This is not critical but needs to be as near as you can get it.
Using a spirit level, a 12 or 14lb hammer and a block of wood (so as not to damage the ends of the tubes) knock the tubes into the ground until they are firm, about 2.5ft depending on subsoil.
Start at one end; use a length of wood and a spirit level to make sure that all the tops of the tubes end up at the same height.
Inspect the tops of all the tubes; remove any damage with a metal file, using a scrap piece of poly pipe check that it will slide over the end with ease.
Below on Left : (tubes put in position)
Below on right : (tubes hammered in)
Hard work over. Have a cup of tea.
Text & Pictures by Alan P. BR/

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