So, you have decided to build a greenhouse, but you are confused about which type of greenhouse covering would be best for you. Let’s take a look at some of the pluses and negatives of polycarbonate sheets and polyfilm coverings. We will discuss R value, installation, cost and lifetime expectancy.
R value is defined as a materials ability to resist heat flow. The higher the R value, the less energy it will take to heat the same size space under equivalent conditions. This may or may not be a concern to you depending on how you are going to use a greenhouse.
The most common single film used for greenhouses is clear 6 mil, 4 year covering. What this means is that the film is 6 mil thick and that the UV protection is warranted for up to 4 years. There are also some other types of film such as overwinter (this film is meant to last one year), white films (lower light transmission) , and reinforced polyfilm (with a rip stop cord).
The R value of single polyfilm is 0.87. It is the least efficient of all of the greenhouse coverings we will discuss.
Installation can be done in several different ways. If you have a wood frame you can use batten tape and staple through the cover and the tape into your frame. If you have a wood frame or a metal frame you can use the base and wire system. The base is screwed to your frame and the cover is secured using a W or wiggle wire. This is a pretty simple installation, but you want to make sure that you do not try to do this on a windy day. You will need several people to do this depending on the size of the greenhouse.
The single polyfilm will be the least expensive of all of the coverings we will discuss.
This film should last you the 4 years that the UV covering is guaranteed for. The only issue with this covering is that you may get a tear. There is repair tape available for this. But, if you are not there and not able to fix a tear in a timely manner you may lose the entire cover. This is why some people will choose to go with the reinforced polyfilm over the clear 6 mil, 4 year. It has a rip stop cord that will keep a tear from spreading. That way you will be able to fix the tear no matter how soon you are able to get to it.
Reinforced Polyfilm with Rip Stop
You can do a double polyfilm greenhouse a couple of different ways. You can just buy 2 pieces of the film and attach them together. Or, the easiest way to do this is to buy a tube of the polyfilm. This is just a double layer that is already fastened together. The base and wire system is set up to hold up to 6 layers, so this is not an issue. You will also need a poly inflation fan kit to inflate the 2 layers. I have had some people mention that they think this makes the cover tighter and less susceptible to tears. I have no proof of this, but it does seem a logical conclusion.
The R value of double polyfilm is 1.7. This will save you 40% on the energy costs over a single layer of polyfilm.
The installation on this is done in the same manner as a single layer of polyfilm.
This film will basically be twice the cost of the single polyfilm, as you are basically just using a double layer of the same material. You will have the additional cost of the blower fan. These are typically around $200 or less, depending on the size of the greenhouse and the size of the motor needed.
This film may last a little bit longer than the single layer. As I stated earlier some claim that they inflation keeps the film from tearing as easily. The UV protection is rated for the same amount of time as the single polyfilm.
Polycarbonate is the greenhouse covering of my choice. It fits my needs the best of all of the materials. However, a lot of people don’t like it because of its appearance. It is a rigid plastic configured in much the same way as a piece of a cardboard box. It has a sheet on the outside, a sheet on the inside and a rib that runs through between the 2 sheets. The rib in polycarbonate will be straight vs the wavy rib in a cardboard box. This will distort your view. You will be able to see color, but you will not see form clearly. I use the example that you can see a green leaf and a red flower, but you will not be able to make out if it is a poinsettia, geranium, impatiens, etc. Of course the clear polyfilm is not exactly clear either. It will have a hazy type of appearance to it. If you want a clear glass like view, tempered glass is your only option.
Polycarbonate sheets are available in several different thicknesses. 8mm clear twinwall will have an R value of 1.8. 16mm clear triplewall will have an R value of 2.4. This will be the most efficient of the coverings we are discussing.
Installation of this material requires polycarbonate H profiles to join the sheets side by side and polycarbonate U channels to close off the ends. You will need more framing for this material vs polyfilm greenhouses. Typically polyfilm greenhouses will have 4′ or 6′ wide spaced bays. You can do the same with the polycarbonate, but you will need to run purlins between the rafters spaced according to your snow load needs. There are charts available to determine this. You can typically install this with 2 people as the sheets are not heavy and you install one 4′ wide or 6′ wide sheet at a time. You still do not want to try to install under windy conditions as the sheets can be caught by the wind and sail away.
This will be the most expensive of the coverings discussed in this article. But, it will be the longest lasting. Depending on the manufacturer polycarbonate sheets have between a 10 year and 20 year warranty on the UV. Most sheets also have a 10 year warranty on hail damage, so no need to worry about tears. The practical life expectancy of this material is 20 – 25 years.
When considering which of these materials to use to cover your greenhouse you should look at the initial cost, the cost to install, the cost to heat the greenhouse, and the life expectancy of the material. Once you have made these decisions you should be able to choose the best covering for your greenhouse with ease.
Greenhouse Glazing Materials, Warranty vs Life Expectancy
I get asked a lot about how long certain greenhouse coverings will last. The thing is, the limit of the warranty does not equal the life expectancy of the material. I will address the following materials – 6 mil, 4 year polyfilm, reinforced polyfilm and polycarbonate sheets. I will be mentioning the UV protection. That is what keeps the materials from getting brittle, cracking, or turning yellow. The warranty will typically cover how long the manufacturer expects the UV protection to last, or it may refer to how much the UV protection may change in a certain period of time.
Greenhouse polyfilm is typically listed by the thickness and the length of the time that the UV protection is warranted for. 6 mil, 4 year polyfilm is 6 mil thick and has a UV protection that is warranted for 4 years. But, that does not necessarily mean that it will last the entire 4 years. The material will not get brittle, etc, but if it is damaged (due to a falling limb, hail, etc) there is a possibility that the cover will be lost. There is patching tape for the film coverings, but if you are not at the greenhouse when the damage occurs it may be too late to stop it. This will be the least expensive of the greenhouse glazing choices and is excellent for small hobby or commercial greenhouses. Although most of the commercial greenhouses will use a double layer of this film with a blower that blows air between the 2 layers. This will definitely increase the insulation factor for this material. I have had some growers report back to me that they feel the film is less likely to be damaged when using this double layer. They feel that the air between the layers “stretches” the film, making it tighter and less susceptible to damage from falling items.
The reinforced polyfilm is 2 layers of film laminated together with a rip stop feature in between the sheets. This has a one year warranty on the UV protection. But, we have had reports back from people who have gotten up to a 12 year lifetime from this material. The rip stop feature is what makes this possible. If the film does get a tear it cannot go any further than the cords of the rip stop. That will keep the area of the rip limited, and it is easily repairable once it is found.
Polycarbonate sheets are a rigid material. Many manufacturers offer a 10 year warranty that the light transmission will not vary more than 10%. The change in the light transmission is what causes the sheets to get brittle, yellow and crack. There are, however, some manufacturers out there now offering a comparable 20 year warranty. Please be sure to check with the company supplying you the sheets to see which warranty is offered. Polycarbonate is a tough material and typically has a 10 year warranty against hail damage. So, tearing or damage to the sheets is not near as big an issue as the polyfilm. In fact I have been dealing with polycarbonate sheets for over 20 years now and have never been involved in a warranty claim. I have had many people in the industry report back that they have seen polycarbonate sheets (with the 10 year warranty) last up to the 20 year mark. I personally have seen the 10 year warranty material remain usable at 15 years.
Hopefully this overview of the warranties and greenhouse glazing materials will give you the information you need to make the best decision for your greenhouse.
The same thing happens every year about this time. We are all still enjoying the warm weather of summer, getting the kids ready for school, and we forget about our beloved plants. I can’t tell you how many times in the past that Tom and I were installing greenhouses in the cold of the winter because they didn’t get ordered in time. Typically a greenhouse that is manufactured for you will take from 4 – 6 weeks for delivery. In the fall these lead times become extended, causing delays from the expected delivery times. This not only applies to greenhouses, it applies to polycarbonate sheets as well. They are typically delivered in 1 – 2 weeks, but in the fall they will take a week or sometimes longer past these times. So, even though it is really hard to think about it right now, if you are considering purchasing or building a greenhouse this fall, now is the time to start your decision process and get an order placed. Trust me, this I know from years of experience.
Yep, That is Tom and my greenhouse. We really do practice what we preach. We think everyone in America should own a greenhouse! This was a rare snow storm in SE Louisiana. I don’t think the neighbors could even believe that we were outside in this mess. Today I just wanted to take a minute to reflect on the beginning and growth of Advance Greenhouses. Fifteen years ago Tom and I were studying how to get on the internet. We knew the product we were interested in, as we had been selling and installing greenhouses for a while. Our first adventure with polycarbonate was in 1993. We got a book about 4 inches thick on how to set up a website and dove into it. What in the world language were those people using? Something I had never heard of before. I am sure we fought and cussed our way through it and came up with what was an absolutely horrible website. But, people started to find us. We also did a lot of local garden shows to put the word out. Fifteen years later, here we are. Through the years we have had the pleasure of speaking and working with many like minded people. We love flowers, but we also love fresh food that we have grown for ourselves. Our greenhouse has been multi faceted. We have stored my cherished hibiscus plants, started seeds for the garden, started annuals and perennials for the flower gardens and even grown some food hydroponically in our greenhouse. As I tell people, it is a learning curve to figure out exactly what will work in your greenhouse. There are some hard, fast rules, but we are all growing different plants under different circumstances. We all have to do a little bit of experimenting to figure out what works exactly for us. In closing, we are running some sales this month as a customer appreciation (also an appreciation for what we have thanks to all of you). Visit our website to see the specials. Our business is very personal and very rewarding for both of us. Thank You! Tammy and Tom
Today’s edition of Polycarbonate Glazing Tips addresses Lexan Softlite and Polygal Polymatte. Both of these sheets have 100% light diffusion. This is an excellent choice for commercial growers or homeowners looking for healthier plants, increased yields and faster growing times. The sheets will spread the light out so it is evenly distributed to all parts of the plant, even under the canopy. Selections are available in corrugated, 8mm and 16mm sheets.
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