Considerations for Polytunnel Purchase
Turnkey Projects
Polybuild have a team of people, to take a project from the initial polytunnel enquiry, through to completion. We can organise all the necessary planning applications and sub contractors.
Planning Permission
Planning requirements vary with each local authority and location. It is most likely that your proposed polytunnel structure will require planning permission (even in the most basic form of notification).
We do recommend planning permission be obtained prior to purchasing a polytunnel structure to ensure the correct polytunnel specification is chosen to meet any specific planning requirements.
We will assist with advice and are happy to produce specific drawings to support your polytunnel planning application.
Polytunnel Foundations
On polytunnels larger than 4.3m (14') in span, it is essential to have the foundation tubes anchored firmly in concrete. The volume of concrete required to set foundation tubes increases proportionally to the span size of the polytunnel structure, we can advise the volume and specification of ballast accordingly. Foundation tubes can be supplied ahead of a polytunnel structure for early site preparation upon request.
Polytunnel Post Types
As the polytunnel structures increase in size, larger diameter posts must be used for increased strength. As standard, most polytunnels are supplied with round tubes. Sometimes we use twinned round tubes. On larger multispan polytunnels we can use round tubes but for additional strength rectangular or square section posts are substituted.
Polytunnel Cladding Systems
Three main methods of used to fix cladding material to the polytunnel are as follows: -
- Trench & Bury a low cost traditional method for smaller polytunnels where a trench is dug a spade deep and a spade wide for the polythene to be laid in and back-filled with the spoil, following this the hoops are raised to tension the polythene. This method offers limited flexibility especially if digging is difficult or the polytunnel structure is long.
- Timber rail for ground, side & end rails - a tanalised timber rail is attached to the polytunnel structure at each hoop with pressings secured by through bolts. The polythene cladding is wrapped around a timber batten which is then nailed to the timber rail. It can then be tensioned by sliding the rails down the hoops and tightening the fixings.
- Aluminium Grip-Rail for ground, side & end rails – an Aluminium box section rail with an integral 'T' slot for sliding in bolt head fixings. The polythene is held by a two piece PVC in-fill strip to secure the cladding material. Aluminium rails offer a strong rigid fixing without cutting the polythene and make easy work of cladding the polytunnel.
Polytunnel End Types
- Timber Ends are the cheapest option, with either 2 or 4 uprights (dependant on width) and a lintel per end. Polythene is rolled round battens and nailed to the timber posts and rails.
- Steel Ends are the smartest option. Polythene is clipped into an aluminium rail, there are 2 or 4 steel uprights (dependant on width) and a steel lintel.
- No Ends An aluminium rail is fixed onto the end hoop and the polythene is attached to the rail.
Anti-Hot Spot Tape
Anti-Hot Spot Tape (AHST) is an over-hoop foam insulation tape with a slippery surface coating. AHST is applied to all steel frame components that are in contact with the polythene cladding. This is essential to reduce heat transfer & abrasion thus dramatically increasing the life of the polythene.
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Polytunnel Cladding Materials
All supplied polythene is guaranteed against any manufacturing defects for 5 years and we do recommend to budget for replacement every 5 years although sheets will usually last up to 7 years under normal conditions. Polythene repair tape is available to help prolong polythene life.
The following polythene sheeting options are available 'cut to size' through Polybuild.
- Clear transparent 720 gauge. This allows maximum unfiltered light through and is the standard budget option.
- White 720 gauge with a light transmission of 65% (ideal for nursery stock) which require shade and a cooler environment. Very suitable for retail shade areas and sheep housing.
- Clear Politherm AF 720 gauge. Enhanced energy saving and anti-condensation droplet formation. Politherm will provide 2 - 3 degrees Centigrade higher temperature than clear polythene. Politherm also provides improved light levels particularly in spring and autumn by 10 - 15%. Politherm is particularly suitable suitable for crops requiring high light levels i.e. tomatoes, peppers and cucumbers.
- Luminance THB AF 800 gauge. Providing diffused light to increase growth and yield, Infrared solar radiation is screened out to keep the environment cooler without a similar reduction in photosynthetic radiation. An anti condensation additive is applied to the interior surface of the film and the cloudy finish to this material helps reduce scorching on hot summer days. With a high light diffusion this film is recommended for a variety of crops especially nursery stock, ornamental / bedding plants and strawberries.
- Other Materials. Polybuild supplies a whole range of other cladding materials, in rolls or as sewn sheets. Most have a longer life span than standard polythene and some are flame retardant. Please contact our sales department for further details 01903 892333.
Polytunnel Crop Supports
For crops that need support, crop bars will carry wires running the length of the polytunnel. These will support growing crops, hanging baskets or irrigation systems.
Fitting Crop Supports will improve the rigidity of your polytunnel, although not essential, Crop Supports will improve the wind speed handling by approximately 10% and snow loading can be increased by up to 50%.
Polytunnel Door Options
- Ruche Up Flaps are suitable for the 'popular' range of polytunnels. Ruche up flaps are the simplest & cheapest end enclosures and comprise of a polythene blind reinforced with timber lathes which slide in a simple guide.
- Timber Door Panels are made from truss grade tanalised timber, 90mm x 40mm cross section. They are factory assembled via mortise & tenon joints and clad with "Correx" rigid plastic sheeting.
- Steel framed doors are welded from 32mm x 32mm box section steel and then hot dip galvanised. The steel frames are clad in PVC Biolex rigid plastic.
- Hinged Door kits come complete with galvanised "T" hinges, handles, tower bolts, drop bolts, auto latches and door stops.
- Sliding Door kits come complete with aluminium extrusion combining door track and drip proof hood. Quadruple sealed bearing carriages support the door from above. Steel bottom guides prevent the door swinging in the wind.
Polytunnel Ventilation
See the ventilation section
Delivery
Larger polytunnel structures are delivered using our own lorry, whilst smaller structures are sent using a carrier.
Installation of Polytunnels
Our professional installers can install your polytunnel for you, however many customers are keen to install the structure themselves. Full instructions and a parts breakdown are sent on delivery.
Polytunnels and Exposed Sites
If you are on a very exposed site the wind speed handling can be improved by reducing the hoop spacing - available as an option for each structure. By adding the optional Crop bar supports, wind handling will be increased by about 10%, and on larger structures longitudinal tie bars can be fitted to further tension the unit as a whole. |