Harrisville Primary School Greenhouse
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A Bit of History
of you who know us from the early days know that we initially
began Hunkin Garden Products Ltd selling domestic glasshouses
imported from Halls in the UK. We stopped selling glasshouses
some time ago because we could no longer get glass at a realistic
price from NZ suppliers. We looked at importing our own glass,
and while we could have done this, freighting glass around the
country without breakage seemed impossible. Time has moved on
and the kids you see in the picture can now be seen on our Miniature
Hereford page 10 years on. The little girl in the purple gumboots
has a Bachelor of Social Sciences in psychology degree and is
now studying to become a Master of Science. The little boy is
a student and the computer Guru at the local college where he
sets up and maintains the school's computers and network.
After 19 years we now have our own range of
greenhouses. As my father, a retired fitter turner says "there
is no substitute for experience" and we have used our experience
to design a stronger, higher side-walled greenhouse using 6mm-twin
wall polycarbonate. By having these greenhouses made in China
for us all these improvements have been made at a very competitive
So what are the benefits or polycarbonate over glass? It is
a "no brainer" really.
Safety has got to be number one, especially if there are young
children playing in your backyard. Polycarbonate is one of the
toughest coverings around. Polycarbonate protects against rocks,
hail, and can even withstand the impact of a baseball that may
have ventured into your yard. It can also withstand a heavy
snow load. The safe nature of polycarbonate makes our greenhouses
ideal for schools.
Lightweight so we can supply much bigger pieces, which means
glazing, for want of a better word, is much easier. Instead
of 106 panes of glass that we used to have in a 12 x 8 greenhouse
for instance, we now have 36 large pre-cut polycarbonate sheets,
meaning fewer air gaps to leak air and less fiddling around
fitting little panes. Your greenhouse is assembled in no time
Diffused light every gardener knows plants need light to grow.
It is a vital part of the photosynthesis process. What is not
so commonly known is that plants often grow better under diffused
light because light tends to be scattered and leaves pick up
light from all directions. There have been claims of 20% to
30% increases in growth with diffused light. Direct light on
the other hand can often cause burning of the leaves, which
reduces growth. The twin-wall polycarbonate diffuses the light
so your plants are unlikely to get burnt in bright sunlight.
No need to paint the outside to prevent scorching or erecting
shade cloth in summer.
Energy saving - The more heat the greenhouse retains, the better,
especially if you want to heat the greenhouse. (See our comparative
table below in the frequently asked questions). There is also
less condensation, and little or no dripping from overhead.
Every greenhouse comes with a 10-year guarantee on the aluminium
frame against faulty workmanship, much more than you will receive
from most other manufacturers. The polycarbonate is guaranteed
in N.Z. for 7 years against breakdown (going brittle) by U.V
degradation. If U.V breakdown occurs, and is confirmed by the
manufacture's sample analysis, a pro rata replacement credit
will be allowed. A credit will be issued, based on original
invoiced value, for the unused period of the warranty. Warranty
is to the original purchaser of the greenhouse. The polycarbonate
must be installed with the UV coated side to the outside (facing
the sun) otherwise the warranty is void.
By purchasing one of our greenhouses you are making a long-term
investment that will bring you many years of enjoyment and service.
With unbeatable durability, safety, insulation and pricing,
what are you waiting for?
Here is what Marie had to say about our greenhouses
have been looking to buy a green house for several years now
and finally bought one off you a few months ago. We are extremely
happy with the green house. It arrived in perfect condition.
We employed our friendly fencer to put up the base, so it was
concreted in and extra reinforcing in each of the corners. We
completed the rest ourselves (with no building experience).
We went to the garden show at Manfield (Manawatu) recently and
once again looked at green houses (there were 3 different types).
There was no comparison. The green house I bought from you is
far superior. The height side walls and strength were very obvious.
Thank you for a great product."
Frequently asked questions
What is polycarbonate?
Polycarbonate belongs to the group of plastics called thermoplastic
polymers. It is not to be confused with acrylic, which is a
much cheaper and inferior product. Polycarbonate is widely used
in industry because it has excellent temperature resistance
(125 Celsius to minus 40 Celsius), impact resistance (250 times
stronger than glass, virtually unbreakable) and optical properties
(80% of visible light, glass transmits 89%) which makes it ideal
for greenhouse applications. It is non-toxic, stain resistant
and weighs six times less than glass.
The use for Polycarbonate is almost endless. Here are a few
applications. Bulletproof windows as used in banks, safety glasses,
crash helmets and prescription glass lenses. CDs and DVDs are
made from polycarbonate. Ever tried to break one?
Will the polycarbonate get brittle after long exposure to
sunlight like other plastics?
Don't confuse polycarbonate with the cheaper acrylic plastics
that are available. The polycarbonate has a UV treatment on
one side that must face the sun. We give it a seven year limited
warranty, but polycarbonate products used for roofing in NZ
(Laserlite TM corrugated roofing for instance) is advertised
with a lifetime warranty. www.laserlite.co.nz.
What is horticultural glass?
Horticultural Glass is made by the rolled glass process
and is the cheapest form or glass. A continuous stream of molten
glass is forced between water-cooled rollers to get the correct
thickness. Horticultural glass often has optical imperfections
and sometimes depending on the source, is not as clear as window
glass (sometimes a bit green).
When horticultural glass breaks it splinters leaving sharp
jagged edges which must be handled with great care. Care must
be exercised when handling glass and you should always place
a gloved hand under the glass so it can't slip. If glass ever
shatters in your garden or on the lawn, that is the last time
you will ever be able to run around with bare feet, because
you will never get rid of all the glass splinters.
So what's the big deal about insulation?
Greenhouses work by trapping the heat from the sun. If the
heat escapes easily through the glazing or air gaps then the
whole point of having a greenhouse is lost. The best greenhouses
are the ones that can hold the heat for as long as possible.
The polycarbonate sheets fit inside the frames so there are
no air leaks. These greenhouses are the best-sealed greenhouses
I have seen and rivals a tunnel house that has a completely
is 6mm-twin wall polycarbonate?
Two thin sheets of polycarbonate are separated by a 4.5mm
still air gap, much like double insulation used on windows in
colder climates. The construction is like the coreflute used
in plastic real estate signs.
Won't water and bugs get between the twin wall?
The polycarbonate fits inside the frames so bugs and water
can't get in.
Doesn't glass insulate?
It does to a point, because infra red (heat) does not transmit
through glass very easily. Well that's the theory. However we
all know that in order to keep your house warm in winter you
pull thermal drapes across your windows, so it is not that good.
Insulation factors R ratings for different greenhouse materials.
Most people will be familiar with the R rating given for insulation.
Fibreglass insulation for instance ranges from R1.6 up to R
3.6 and more. The higher the "R" number, the better
the insulation. The table shows some comparisons.
Material Insulating "R" number
6mm twin wall polycarbonate 1.5
3mm horticultural glass 0.95
Polythene plastic as used in tunnel houses 0.83
From this table you can see twin wall polycarbonate insulates
50% better than glass traditional 3mm glass and about 72% better
than plastic. In a greenhouse situation the use of plastic is
a bit better in a tunnel house because it is normally welded
so it is quite airtight (no draughts) and glass is a little
worse in a glasshouse (more draughts) because of more joins
(smaller panes) and unavoidable air leaks. Our greenhouses are
so well sealed they rival the tunnel house welded skin for air
What is best for greenhouse frames, aluminium or steel?
The only reason manufacturers use steel for frames in domestic
greenhouses is price. These greenhouses are often made from
electroplated galvanised sheet steel that has been cut and folded
or rolled to shape. The protection layer is very thin, and the
cut edges of course are not galvanised, so though the frames
will last quite a long time, eventually they will rust. The
sheet steel is also quite thin, so where it has been cut there
is often a very sharp edge. The only disadvantage with aluminium
is cost. It is a more expensive metal and dies have to be made
in order to extrude the product to shape. The frames are much
thicker and in most cases have rounded edges from the extrusion
process. Aluminium has a thin protective oxide layer on the
outside that forms immediately the moment the aluminium is exposed
to air. Any damage is instantly sealed off with an oxide layer.
Aluminium never rusts and provided compatible materials are
used with it, there is virtually no corrosion. Aluminium will
last a lifetime, and with the rising cost of raw materials it
is false economy to purchase a greenhouse with a steel frame
that you will eventually have to replace. We have a 10 year
limited warranty on the frame. It is quite conceivable that
a steel-framed greenhouse will have started rusting before our
guarantee has run out.
Before making a decision to purchase a greenhouse look very
closely at the construction so you can make educated comparisons.