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Greenhouses/Glasshouses

A Bit of History

Those 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 is now at university and the boy at college.

After 17 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 this experience to design a stronger, higher side-walled greenhouse using 6mm-twin wall polycarbonate. All these improvements have been made at a very competitive price.

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 72 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 at all.

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.

Our Guarantee

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?

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 welded skin.

What 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 tightness.

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.

If aluminium is best, why do you use steel for the base?
Aluminium is a very reactive metal. When cut aluminium is exposed to air it immediately forms an oxide layer which protects the metal. In the open air this works extremely well but when in contact with constantly damp soil it is not the best choice. The salts in the soil can constantly attack the protective oxide layer that can lead to corrosion. The zinc used in galvanising will also react with salts in the soil. We supply a prefabricated steel base that is not only galvanised but powder coated as well (much like Coloursteel™) so the part in contact with the ground is protected from salts by the baked on paint. The ultimate would be 316 stainless steel (which incidentally protects itself like aluminium does) but you would have to increase the mortgage on your house to pay for it. The base is included in the price.

Before making a decision to purchase a greenhouse look very closely at the construction so you can make educated comparisons. So what is the difference between our greenhouse and others?

Our points of difference

Packaging

The greenhouse comes in three cardboard packages, base, frame and polycarbonate. Frame parts are numbered and individually sleeved in plastic. They are then bundled together so each bundle corresponds to a particular part of the assembly. All cardboard cartons consist of one carton inside the other to give a double layer of protection. We do our best to ensure the product arrives with no damage.

The Base

1/ 150mm high steel base powder coated over galvanised steel. The base increases the overall height of the greenhouse so taller plants can be grown inside. Powder coating over galvanised steel makes the base last. The base is included in the price to makes construction much easier.

2/ Greenhouses must be held to the ground securely so there are multiple fixing points to the ground, not just at the corners. Anytime we have a part of the base longer than 6 feet (1.9m) we have an extra bracket that is concreted into the ground. These extra brackets are thick powder coated aluminium extrusions. The thicker extrusion used for a ground pegs makes the base a lot more rigid and stops the rolling effect often found in other base designs.

The Frame

1/ The aluminium frame is anodised a natural silver colour or powder coated green, a very close match to forest green. This results in a very attractive greenhouse that will never rust.

2/ All the bolts and self-tapping screws are stainless steel. Stainless steel bolts are very strong. The tensile strength of stainless steel is around 515Mpa compared to mild steel 260MPa and aluminium 180MPa. There is no rust and they are much stronger than other materials.

3/ We use 3mm thick aluminium gussets in the corners and the apex. Most greenhouses use 1mm thick aluminium for gussets. This means our gussets are THREE times thicker than gussets in other greenhouses. We then use stainless steel bolts to secure the frame to the gussets. This results in a very strong corner assembly. With our green frames the gussets are painted to match the greenhouse and don't stand out like unpainted ones in some other brands.

4/ Diagonal braces are in every corner and in the roof. Diagonal bracing makes a huge difference to the stability and strength of the structure. If you look closely at pictures of other greenhouses you will see in many cases the braces are absent.

5/ Our diagonal braces are made from 25mm x 25mm x 1mm thick aluminium angle. Others may use smaller braces. This results in a stronger greenhouse.

6/ We have braces across the apex and braces between the sidewalls and roof to give a stronger greenhouse. You won't find many greenhouses that have this.

7/ Most greenhouses have a horizontal piece of framing running across the back wall (plain gable end) to reduce flexing in the back wall. In the Orion 126 we have two of these tying the vertical studs and the corner extrusions together via the 3mm thick aluminium gussets and stainless steel bolts. This gives us a stronger back wall and reduced flexing.

8/ Our vertical framing is approximately every 610mm. Many cheap greenhouses have framing as wide as 720mm. You can easily tell. A 12-foot (3.5m) long greenhouse should have 6 sheets of polycarbonate making up the length of the sidewall. Wider stud spacing results in fewer sheets, normally 5. Less studs means less strength. You would not take studs out of you house to make it cheaper so why would you do it with your greenhouse?

9/ We have a higher apex and side walls than most other greenhouses. This means you can grow taller plants against the side of the greenhouse and back wall. The taller apex results in a more sloped roof making the horizontal roof braces very effective. A higher greenhouse also increases the volume of air inside resulting in a more stable temperature.

10/ Doors have rubber seals to keep in the heat. These greenhouses are often better sealed than a tunnel house resulting in great heat retention.

11/ We use 6mm-twin wall polycarbonate instead of glass. Unparalleled safety and up to 50% better insulation than glass.

12/ The assembly instructions have been initially written by our Chinese manufacturers and we have then modified them using our own construction experience so the instructions are easier to follow. All framing parts have part numbers on them as well as the polycarbonate. We have also added photos of important points to make things clearer.

Pegasus Series

Single door. Price includes base and GST
Measurements are L x W x H (apex) Eave heights are 1.65m including base

Pegasus 66 (1 roof vent) 1.90m x 1.90m x 2.38m $1595.00 Anodised frame, grey powder coat base
Pegasus 66 (1 roof vent) 1.90m x 1.90m x 2.38m $1674.00 Green powder coat frame and base
Freight NI $120, SI $180.00

Pegasus 86 (2 roof vents) 2.53m x 1.90m x 2.38m $1795.00 Anodised frame, grey powder coat base
Pegasus 86 (2 roof vents) 2.53m x 1.90m x 2.38m $1884.00 Green powder coat frame and base
Freight NI $130, SI $190.00

Pegasus 106 (2 roof vents) 3.15m x 1.90m x 2.38m $1995.00 Anodised frame, grey powder coat base
Pegasus 106 (2 roof vents) 3.15m x 1.90m x 2.38m $2094.00 Green powder coat frame and base
Freight NI $150, SI $200.00

Orion 128 and 148 (128 pictured)

(Eave height 1.65m including base)

Orion 128 Double doors, 4 roof vents, 3.78m x 2.53m x 2.55m $2395.00 Anodised frame, grey powder coat base
Orion 128 Double doors, 4 roof vents, 3.78m x 2.53m x 2.55m $2514.00 Green powder coat frame and base
Freight NI $200, SI $250

Orion 148 Double doors, 6 roof vents, 4.40m x 2.53m x 2.55m $2695.00 Anodised frame, grey powder coat base
Orion 148 Double doors, 6 roof vents, 4.40m x 2.53m x 2.55m $2825.00 Green powder coat frame and base
Freight NI $200, SI $250

" Graham - I am thrilled with the product I purchased from you. Instructions were clear & specific. All parts fitted perfectly. "

Accessories

Staging

Staging single $125.00 anodised
Staging single $132.00 green powder coat
Freight NI $15, SI $24

Staging is approximately 1.26 m x 0.5m x 0.75m

Staging double $175.00 anodised
Staging double $182.00 green powder coat
Freight NI $20, SI $34

Staging is approximately 1.26 m x 0.5m x 0.75m

Louvres

Anodised $85.00
Green powder coat $95.00
Freight NI & SI $10

Automating your greenhouse

One of the first things you will notice with a greenhouse is how efficiently it can trap the heat. This is a good thing in winter, but as summer approaches it is very easy to have your greenhouse overheat if you don't have the vents open. The problem is you need to remember to open them, and if you work during the week this can become a bit of a chore. On those frosty days it is very important to close the vents in time otherwise all the heat gathered through the day is rapidly lost.

Fortunately there is a solution. You can install automatic vent openers on your greenhouse vents. These units require no electricity. The mechanism utilises a wax made of plant oils harmless to humans even if licked (though you might need to stock up on toilet rolls) that expands with heat. This expansion pushes a piston rod out of the cylinder that then opens the window. When the temperature falls, the wax retracts and the weight of the window together with the force of the opener's closing spring closes the window again. The opening temperature range is adjustable between 15 and 25 degrees Celsius.

To fit the automatic vent opener to our greenhouses you will have to drill one small hole in the vent frame; the rest fits the existing bolts and holes.

These vent openers are made in Denmark and have a one-year warranty.

Automatic vent opener $125.00
Postage NI and SI $10.00

Coming soon. Fully automatic temperature controlled solar powered extractor fan system developed by Hunkin Garden Products that will suck the hot air out of your greenhouse. Watch this space.

We also stock packs of nuts and bolts, clips and spare sheets of polycarbonate for our greenhouses.

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