but it can be bent onsite if you follow the minimum bending radius charts supplied by the manufacturers. Polycarbonate has typically had a 10 year warranty with a 15 plus year life expectancy. But, there is now a Lexan product which has a 20 year warranty with a 25 year life expectancy. The sheets also typically carry a 10 year warranty against hail. These sheets are virtually indestructible. The installation of polycarbonate requires the use of several different profiles, specifically the U and H profile. The H connects the sheets and the U closes the channels at the top and the bottom of the sheets. The biggest drawback to polycarbonate is the looks. A lot of people do not like the fact that you cannot see through it like you can with glass. Even though the 2 exterior sheets are clear, the rib running between the sheets will distort the view. But, in my opinion, for performance this material can’t be beat. Glass You should always use tempered glass when building a greenhouse. This is a safety glass that will crinkle when it breaks to help prevent injury to users. This is especially important in overhead glass. You will not get as much insulation from glass as you will from the polycarbonate sheets. Single glass vs 8mm polycarbonate will offer about half as much insulation value. You can just about match the R value of double tempered glass with a 16mm triplewall polycarbonate. But, double tempered glass is a very expensive option and is usually an option used more for living spaces rather than greenhouses. Glass normally has a one year warranty on workmanship, but in most cases glass will last a long time unless it gets broken. If that happens the panel should be replaced immediately. Fortunately, the glass panels do not break very often. Tempered glass (sometimes called toughened glass) is stronger than regular float glass and usually only breaks if it is hit with a sharp pointed object. Glass is the most expensive of the options discussed here, with the double glass being at least twice as much as the single glass. Building Your Own Greenhouse Here are a couple of quick hints if you are building your own greenhouse frame. Polyfilm Be sure to use batten tape or a base and wire system to install this. It will hold it much better than just stapling through the film. Polycarbonate The minimum roof pitch is 1 on 12 when using polycarbonate. Be sure to get a specification sheet that states the minimum rafter and purlin spacing for your required wind and snow loads. Glass If you are building your greenhouse using recycled windows, be sure they have tempered glass. You can spot this by finding an etched label in the corner of the glass. Tempered glass is always marked. Conclusion Greenhouses are used in many different manners depending on what you are growing and what the requirements of the plant are. All of these greenhouse glazing materials have their place, just be sure to make the proper choice for your needs. GG