FEATURESTORY
by Tammy Wylie
Choosing the Correct Greenhouse Glazing
I
f you are considering purchasing a greenhouse
kit or building your own greenhouse, one of the
biggest considerations is what type of green-
house glazing will be the best for your needs.
There are several choices, all with different price
ranges and different characteristics. These features
will determine the cost, performance and cost to main-
tain your structure. The most frequently used types of
glazing are polyfilm coverings, polycarbonate cover-
ings and glass. Each has its own set of features and
benefits
Polyfilm
The biggest issue with polyfilm is that some peo-
ple do not purchase polyfilm with a UV protection.
These materials are not designed to be used for long
periods of time in the sunlight and most of them get
brittle and crack and fail within the first year. There
are several different types of greenhouse polyfilm
available commercially. The most commonly used
polyfilm is a 4 year, 6 mil. This means the UV protec-
tion is rated for 4 years and the film is 6 millimeters
thick. There is also a reinforced polyfilm available
which is laminated material with a cord in between
the 2 clear sheets. The cord acts as a rip stop material.
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If you get a tear in the film it will stop once it hits the
cord. This gives you time to do any repairs and avoid
future damage. The UV protection on this material is
only under warranty for one year, but normally will
last much longer. I have had reports back of 12 year
old material still in use on this particular film.
The advantages of greenhouse polyfilm are the
cost and ease of installation. The disadvantages are
that it can tear and that you don’t get as much insula-
tion as with some other materials. A single polyfilm
greenhouse is great in areas with warmer climates. In
colder climates they are great for crops that do not
require a lot of heat. If you are looking to use green-
house film, but want a higher R value, there is the op-
tion of doing a double layer polyfilm covering with an
inflation blower.
Polycarbonate
Multiwall polycarbonate will give you the best
insulation factor of the 3 coverings. It is like looking
down a cardboard box. It has a sheet on the outside,
a sheet on the inside, and a rib running straight be-
tween the 2 sheets. This “dead air” space contributes
to the higher R values. The cost of the polycarbonate
is also between polyfilm and glass. It is a rigid plastic,
www.GardenandGreenhouse.net
November 2018