The Basics of Greenhouse Coverings

By Erik Biksa
Editor-in-Chief
http://www.Grozine.com

Growing in a greenhouse is a great way to extend the growing season or produce crops year round. Greenhouses can be purchased as complete packages—everything you need including detailed assembly instructions to get growing right away.
Lots of gardeners also choose to build their own too. In either instance, the success of a greenhouse largely rests in the type of covering used.
There are lots of different types of coverings available; however, choosing the right one for your application and structure type is something you should learn more about to make an informed purchase.

Greenhouse_filmsHere’s a quick checklist of some of the basic questions you will want to address first:

What kind of light intensity do I want for my crop, and how much natural light can I count on, seasonally?
This is important because some covering allow more light transmission than others. In some instances, growers want to reduce the amount of light their crops receive. Note it’s often better to start with maximum light transmission, because you can add shade cloth or apply shading compounds seasonally to match what you are growing.

Will I be heating the greenhouse, and if so, how expensive will it be to heat based on the heat source and outside temperatures?
If you are going to be needing to do a lot of heating through the year, you will want a covering that conserves heat well. However, the tradeoff is usually less available light transmission for greater insulative qualities.

Is my greenhouse going to be prone to damage from things like hail, falling branches, pets or be situated in a high traffic area?
Puncture resistant coverings are available if you want or need to take an added measure of security to protect your cropping investment. Durability can range from mildly resistant to sledge hammer proof. Expect to pay lots more for the higher security stuff.

What is my budget available, and do I possess the skills to install more elaborate coverings that require hardware, taping, drip rails, etc?
For instance 6mil 4 year poly is really easy, and twin wall polycarbonate can be a little more involved (not to mention costly)

Basic Covering Types:

TuffliteGreenhouse Poly, ie TuffLite IV (6 mil, 4 year low density polyethylene)
Advantages:

available in a wide range of widthsbuildings can be covered or double covered (inflated between layers) in one sheet; limits air and heat loss through cracksdiffuses light; plants grow betteraffordabledurable; treated to withstand outdoor light for a minimum of 4 years, lasting up to 6 or 8 typicallyrepairs are easy with poly repair tapesimple and quick to install (follow the instructions provided with the roll)gets digested over time in landfill by microbes

Limitations:

can be cut, although surprisingly durable and puncture resistantsingle layer does not provide much “R” value for retaining heatdifficult for one person to install covering; can be done with practicerequires replacement after rated lifedoes not require elaborate framing or flashings; easy to secure with polylock or lathing.

Greenhouseglass

Greenhouse Glass
Advantages:

available in a wide range of specificationsoffers some “R” value for heat retentionallows very high levels of light transmissiontempered types are very durablecan be installed by one personlongevity, very infrequent or no replacement required

Limitations:

very costlymay break or shatterlots of panels means a less airtight buildingrequires special flashings and hardwareinstallation is best left to those with experiencetime consuming to installmay create “hot spots” in the plant canopy encouraging crop problemscan only be installed on certain structure types

Semi Rigid Panels (ie corrugated polycarbonate, twin-wall polycarbonate,Solexx ie Solexx)
Advantages:

very durable, puncture resistantlong service lifesingle wall polycarbonate has very high light transmission, lower R valuetwin wall polycarbonate has good light transmission, higher R valueavailable in common widths and very long lengths or rolls (better installation)aesthetically pleasing

Limitations:

initial investment can be highrequires flashings, special hardware, etc to installtransport costs for large sheets (vs rolls) can be expensive, crating required.

9 Tips and Tricks for Greenhouse Coverings:

For insulating qualities it’s tough to beat double poly—use a seasonal double layer when it gets cold if spending a lot on heatingPoly allows you to roll up the walls as needed; roll up side walls are a great way to keep things cool and healthy with natural ventilationYou can add interior curtains to shade or help keep heat in as needed—covering doesn’t have to “do it all”Install poly when it’s warm—as it cools down it will contract and tighten to a glass like consistency over the building, ie no wrinklesUse Foil Tape to seal up the ends of twinwall coverings to avoid any condensation from occurring in the panel layersFor poly, rolls up to 148’ long are commonly used by commercial growers—this size of roll can have some weight to heft aboutYou can shade your greenhouse with paint-on shading compounds that last a specified amount of time under normal condtionsFor estimating fasteners, count on around four fasteners per square foot when securing polycarbonate over the area of the entire buildingConsider using a variety of material types, for example 4 mm thick twin wall for the end walls (Solexx), doors or other high traffic areas and cover the roof with 6 mil 4 year poly (TuffLite).

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