A high quality greenhouse covered with multi-wall polycarbonate sheets provides numerous benefits to the grower. The material has very good insulating values that allows 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:
- Durability, very strong and long lasting.
- Lighweight and easy to work with.
- Reasonably priced and simple to install.
- UV Protected. Prevents yellowing and premature degradation.
- Used in the construction of qounset, A-frame, straight wall gable roof, gothic style greenhouses, and cold frames.
- Also suitable for building a sun room, enclosing a patio, or installing a roof over a swimming pool.
- Suitable for both residential and industrial roofing applications.
Multi-wall polycarbonate sheets are available in several colors and a 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. Opal is also suitable for rainforest and under canopy type plants such as bromeliads, orchids and epiphytes.
Choosing the correct thickness of polycarbonate sheet depends on several factors. If you live in the north and get a lot of snow then your 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 basically 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.
Recycled Polycarbonate Sheet
Everyone should practice good recycling habits. Recycling is good for the planet and for future generations as well. But when it comes to polycarbonate sheets for roofing, greenhouse, or other outdoor applications, recycled might not be the best way to go.
Many of the no name, generic or fly by night operations offer cheap recycled polycarbonate sheeting. It ‘s 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. While cheaper recycled sheets can start to discolor and weaken within the first year or so.
So investing in a premium product to start with 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.
The best place to start though might be with the frame. 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 nornally 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 is kind of like a rubber gasket. The umbrella washers flatten out when compressed and seal the screw holes to prevent leaks.
As mentioned previously 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 arrangement leaves the ends of the sheets open, hence 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 long U profiles.
H profiles are used to join two sheets together. So if you’re building a wall for example that’s 8 feet tall and 12 feet long, you could use three sheets of polycarbonate measuring 4 ft wide x 8 ft long. You would have two 8 ft long seams where the sheets joined together. So you would need two 8 ft 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. These are used on polycarbonate roofs too.
Another type of profile that’s commonly used when building a greenhouse or similar structure is a “ridge profile” These are used on the ridge or highest part of the greenhouse where the two sides of the roof meet. These 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.
When planning to build a greenhouse, the covering is just one small part of it, although one of the most important. 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, will all cost money too. Setting up a greenhouse can be done in stages though and doesn’t have to be done all at the same time. So concentrate on the greenhouse structure first and then work on the other items as time, and budget allows.