Apr
27
2016

The Basics of Greenhouse Coverings

By Erik Biksa
Editor-in-Chief
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 widths
  • buildings can be covered or double covered (inflated between layers) in one sheet; limits air and heat loss through cracks
  • diffuses light; plants grow better
  • affordable
  • durable; treated to withstand outdoor light for a minimum of 4 years, lasting up to 6 or 8 typically
  • repairs are easy with poly repair tape
  • simple 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 resistant
  • single layer does not provide much “R” value for retaining heat
  • difficult for one person to install covering; can be done with practice
  • requires replacement after rated life
  • does not require elaborate framing or flashings; easy to secure with polylock or lathing.

Greenhouseglass

Greenhouse Glass
Advantages:

  • available in a wide range of specifications
  • offers some “R” value for heat retention
  • allows very high levels of light transmission
  • tempered types are very durable
  • can be installed by one person
  • longevity, very infrequent or no replacement required

Limitations:

  • very costly
  • may break or shatter
  • lots of panels means a less airtight building
  • requires special flashings and hardware
  • installation is best left to those with experience
  • time consuming to install
  • may create “hot spots” in the plant canopy encouraging crop problems
  • can only be installed on certain structure types

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

  • very durable, puncture resistant
  • long service life
  • single wall polycarbonate has very high light transmission, lower R value
  • twin wall polycarbonate has good light transmission, higher R value
  • available in common widths and very long lengths or rolls (better installation)
  • aesthetically pleasing

Limitations:

  • initial investment can be high
  • requires flashings, special hardware, etc to install
  • transport costs for large sheets (vs rolls) can be expensive, crating required.

9 Tips and Tricks for Greenhouse Coverings:

  1. For insulating qualities it’s tough to beat double poly—use a seasonal double layer when it gets cold if spending a lot on heating
  2. Poly 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 ventilation
  3. You can add interior curtains to shade or help keep heat in as needed—covering doesn’t have to “do it all”
  4. 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 wrinkles
  5. Use Foil Tape to seal up the ends of twinwall coverings to avoid any condensation from occurring in the panel layers
  6. For poly, rolls up to 148’ long are commonly used by commercial growers—this size of roll can have some weight to heft about
  7. You can shade your greenhouse with paint-on shading compounds that last a specified amount of time under normal condtions
  8. For estimating fasteners, count on around four fasteners per square foot when securing polycarbonate over the area of the entire building
  9. Consider 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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