A high quality greenhouse covered with multi-wall polycarbonate sheets provides numerous benefits to the grower. The material has excellent insulating values that allow the grower to start their season earlier and finish later in the year. Additionally, polycarbonate sheeting provides security from vandals as well as protection from nuisance pests. It allows the grower total control of their growing environment.
Here are a few more reasons why so many growers use multi-wall polycarbonate sheet for building greenhouses:
Multi-wall polycarbonate sheets are available in several colors and thicknesses. The most popular color for growers is clear. Opal is normally preferred by nurseries and retail centers that just want to keep the plants healthy but not necessarily encourage excessive growth.
Choosing the correct thickness of polycarbonate sheet depends on several factors. If you live in the north and get a lot of snow then you’re going to need a stronger roof with a higher snow load value (this means thicker sheets and more roof supports or “purlins”). If you live in the south you can get by with thinner sheets and less roof support. Generally 16mm sheet is used in the northern areas and 6mm and 8mm is used in the southern regions. The thinner sheets are even used in the Mid-Atlantic States with sufficient roof supports. Polycarbonate sheets can normally be ordered in 4 ft. or 6 ft. widths and in lengths up to 20+ ft.
To install them you just trim the sheets to size using a razor knife or fine toothed saw. The sheets are then fitted with the trim pieces. The two most common pieces are the H and U profiles. The H profiles are strips that are used to join two sheets together, normally on the long side. The U profiles are used on the top and bottom ends of the sheets to keep bugs and dirt out.
Recycling is good for the planet and for future generations, but when it comes to polycarbonate sheets for greenhouse applications, recycled might not be the best way to go. Many of the generic or fly by night operations offer cheap recycled polycarbonate sheeting. It is normally made from ground up water bottles and cd cases. Whether UV protected or not, it simply will not last as long as a premium polycarbonate sheet made with virgin polycarbonate resins. A premium sheet normally carries a 10 year guarantee but frequently lasts for 2-3 times as long.
Cheaper, recycled sheets can start to discolor and weaken within the first year or so. Consequently investing in a premium product from the beginning will likely give you more satisfaction and cost you less money in the long run. Cheaper recycled polycarbonate sheets would be best reserved for use in indoor, climate controlled projects. And when considering the total cost of a fully equipped greenhouse, the greenhouse covering is just one small part of it.
A greenhouse frame can be made out of treated 2” x 4”s, steel supports, or even PVC tubing. Building a greenhouse with polycarbonate isn’t much different than building a shed and covering it with plywood.
Polycarbonate sheets require different types of accessories and fasteners than other types of coverings. The fasteners used with polycarbonate sheets are normally either wood screws (for wood framed greenhouses) or self-tapping metal screws (for metal framed greenhouses). These are used in conjunction with an “umbrella washer” which works like a rubber gasket. The umbrella washers flatten out when compressed and seal the screw holes to prevent leaks.
There are two main types of trim or “profiles” that are used with polycarbonate sheets: U Profiles & H Profiles.
A “U” profile is normally used on the short ends or top and bottoms of the sheets to seal them and keep bugs and dirt out. Multi-wall polycarbonate sheets are hollow inside (the dead air space improves the insulation value of the sheets) and have flutes running the length of the sheets. This type of construction leaves the ends of the sheets open, creating the need for U profiles. The U profiles are friction fit but they should be secured with a bead of polycarbonate grade sealant. A 4 ft. wide x 8 ft. long sheet would require two 4 ft. U profiles.
H profiles are used to join two sheets together. For example, if you are building a wall that’s 8 ft. high and 12 ft. long, you could use three sheets of polycarbonate measuring 4 ft. wide x 8 ft. long. There will be two 8 ft. long seams where the sheets joined together, creating the need for two 8 foot long H profiles. The H profiles would be screwed to the wall supports and the polycarbonate sheets would slide into the grooves in the H profile. This same technique is used on polycarbonate roofs too.
Another ridge profile is another type of profile commonly used to build a greenhouse. These are used on the ridge or highest part of the greenhouse where the two sides of the roof meet. They have a groove on both sides like the H profiles that the sheets slide into, but they are angled to conform to the shape of the roof.
The covering is a small but important part of constructing a greenhouse. Besides the covering and frame, the floor (whether a concrete pad or pea gravel), the plant tables, shade cloth, benches, heating, humidification and cooling equipment, should be included in the budget too.
Constructing a greenhouse can be done in stages doesn’t need to be all at once. Concentrate on the greenhouse structure first and then work on the other items as time and budget allows.
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