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.
There are a lot of reasons to build your own polyfilm greenhouse rather than buying a kit. You may have a special feature or size that you cannot find in a kit. Maybe you have some materials you can recycle. Or, you may just enjoy letting your creative juices flow and making your greenhouse from your own hands with your own design. There are a few basic steps you should follow making decisions regarding your greenhouse whether you are using a kit or building your own design.
You should pick the proper location for your greenhouse. This should be a clear, sunny spot on a nice level location. The ends of the greenhouse should be situated facing north and south.
This is always a major decision when getting a greenhouse. The rule of thumb is – go one size larger than you think you will need. We are, after all collectors and experimenters. We may see the perfect plant at a sale that we just can’t resist. Or, we may find our next best go to variety of tomato or other vegetable that we just have to grow this year. Try to either mark out on your land how you think your plants will be arranged, or do this on a piece of paper. Consider whether you will be having raised beds, containers or hydroponic systems.
Will you build your frame using pvc pipe or galvanized pipe?
If you are using pvc pipe you should use schedule 40 pipe. The simple way to do this is to place a 3′ piece of rebar (sticking out of the ground 12″) where the ends of the hoops will be. Two people are needed for the next step. Place each end of the pipe over the rebar and make your hoop. Your hoops should be placed 4′ to 6′ apart. You will need to use purlins for your frame as well. These are what hold the pvc hoops together. If you skip the purlins you will just have a row of hoops with a cover over them. There is not much structure to this. A minimum of 3 runs of purlins should be used running from one end of the greenhouse to the other. Usually you have one right in the center of the greenhouse with one run along each side where the greenhouse is starting to “bow”. You can use special pvc fittings to tie these together. Most people will use treated lumber to run along the bottom of the long sides of the frames. You can frame out your ends with pvc or with wood. You can build your own door using pvc for framing, or use a purchased (or recycled) wood door. Please note: This style of greenhouse should not be used in high snow load areas. There is a tendency for this type of structure to collapse under heavy snow loads.
Galvanized Pipe –
There are pipe benders available to make specific width of greenhouse bows. Choose the appropriate one for your needs. You will install ground pipe 2′ into the ground with 2′ above the ground. Install your hoops at 4′ or 6′ increments. Install your purlins. You can use a board at the bottom of the sidewalls. The process is basically the same as with the pvc pipe, just different materials. The end walls can be framed out of wood. Although this structure will obviously not have any snow or wind rating, it will be stronger than the pvc frame.
Choosing Your Cover :
There are several different types of covers. The worst choice you could make is going to the box store and buying a roll of film off the shelf. This is great film, but it is just not designed to be used for a greenhouse. There is no UV protection on it. The sun is what breaks down the material. You will be lucky to get one year out of this type of covering. The most commonly used material is a 6 mil, 4 year greenhouse polyfilm. This means that the film is 6 mil thick with a UV covering rated for 4 years. There is also a reinforced polyfilm covering. It has a rip stop feature that will stop a tear once it hits the reinforced cording.
Single vs Double Cover:
You can use either one layer of polyfilm, or a double layer of polyfilm. For the double polyfilm a blower will add air between the layers increasing the insulation factor of the covering. Most people even say that they feel that this makes the film more resistant to tears because it makes it tighter.
Fastening Your Cover:
There are several ways to fasten your cover to the greenhouse. The piece over the top should go from ground to ground.
You can use batten tape to fasten the film to the bottom boards. You will place the batten tape over top of the cover and staple through the tape and the cover. Be sure to have your film tight, but not to taught. An overstretched cover has a tendency to tear.
This is a 2 part system consisting of a metal base (kind of like a c configuration) with a w wire or wiggle wire. You can fasten the base to your side boards. The base will also bend enough that you can fasten it to your end walls. Pull the cover over top of the base and work the “w” wire in with a wiggle motion. This is a good secure fastening system and will work well with a double polyfilm covering.
Don’t forget to address ventilation. Most people will frame out an opening in the front walls and back walls for exhaust fans or intake shutters. The exhaust fan should go up high in the back wall with the intake shutters down low on the opposite walls. These are usually wired to one thermostat so that they come on at the same time. You may choose to go more low tech and use a roll up curtain along both side walls.These are also available as solar powered systems which require no electricity.
There are times when a heater is not necessary for a hoop house. It depends on the type of crops you are growing and what time of year you are trying to grow them. Cole crops can be grown in hoop houses in the winter often without any supplemental heat at all. On the other hand, if you are trying to grow tomatoes or peppers in the winter you will need supplemental heating.
Building your own polyfilm greenhouse will be a rewarding experience not only while you are building it, but also while you are using it to grow your own crops.
Here in Louisiana we call it Lagniappe [lanˈyap]. It’s a little something extra……for free! Everyone loves free. I get asked all of the time how to build your own greenhouse. So, today I have gathered together 10 free greenhouse plans for you. Not everyone can afford or needs a glass greenhouse kit. Tom and I have reviewed the plans and have added our comments to each. These comments are based purely on our years of experience building greenhouses. We have not received any compensation of any kind from any of these plans. So, enjoy and get busy building a greenhouse this week. Please keep in mind that as far as we know no engineers were involved in these plans. In other words, we do not feel that any of these plans have been built with heavy snow and/or wind loads in mind. Also, as a general note: A lot of the plans mention using plastic sheeting that is not UV protected. Don’t expect any more than 1 years use out of non UV protected plastic. We always recommend using 6 mil, 4 year polyfilm to cover greenhouses. With the appropriate waivers in place, let’s get busy building!
California Style Roof Greenhouse
California Roof Style Greenhouse Plans – We used to sell and install sunrooms. That is how we really got started with greenhouses. Anyway, we used to sell a sunroom that looked like this and it was called the California Roof Sunroom. These plans seem very thorough. They even tell you how to square up your base. It is a bit distracting to try and read the plans on their website due to all of the ads, etc. But, they do offer a downloadable set of plans (ad free) for $5. Might be nice to have these to take to the jobsite.
YellaWood Greenhouse Plans
YellaWood Greenhouse Plans – These plans are from the manufacturer. They do give you a lot of specifications about the building materials, but the plans are pretty much a line drawing with measurements. If you are an experienced builder, you probably would not have much trouble with this. If you are a beginner and need more detailed instruction, this might be one to pass on.
Barn Style Greenhouse Plans
Barn Greenhouse Plans – They state one weekend for this. I am a bit skeptical of that time frame. This greenhouse has a lot of miter cuts and will require what seems like a lot of fitting to me. But hey, who can resist the looks of a barn style greenhouse?
Raised Garden Bed with Removable Cold Frame
Raised Garden Bed with Removable Cold Frame – This is a super plan and will work nicely along side of a standard garden and greenhouse. They are stating a 10 – 15 degree increase in temperature inside the cold frame. This is a great project for someone with limited space, or someone who just wants to get a head start on the garden.
RunnerDuck Greenhouse Plans– I really like the looks of this greenhouse, although I am wondering what it would look like with a small overhang on the roof on all sides. He has stated that you can adapt this to make a freestanding greenhouse with these plans as well. I do like the dutch door feature and the fact that he used a roof vent with an automatic opener.
Bamboo Greenhouses Plans
Bamboo Greenhouse Plans – What a great way to use bamboo! I would suggest using batten tape also when securing your film to your frame. I am not really crazy about using a door that is secured with velcro. If you are in a high wind area I would think this would give you problems. Other than that a great simple plan.
GeoDome Greenhouse Plans
Geo Dome – This may not be for a beginner. Lots of angles to cut for the frame to fit together properly. But, who doesn’t love the look of a dome greenhouse? Sounds like they did a whole lot of research before designing this. If you have some skills and time I would consider this plan.
$50 Greenhouse Plans
$50 Greenhouse – Of course this is if you can recycle a whole bunch of materials. But, he states that even with new material you can build this for around $200. If you are in an area with high snow be sure to look at the picture of what happens when you get a couple of inches of wet snow. His greenhouse collapsed. So, I would definitely rule this one out for snowy areas.
In closing, my first, and second greenhouses were both ones that we built ourselves with our own plans. They were both covered with clear plastic (non UV) film. We did not know where to get the UV protected film at that point. One year is the life expectancy of the non UV material. I wish at the time we would have known the difference, but we just kept recovering. Also, not to tell tales on myself, but at the time we were building these greenhouses there was no internet and no free plans. What a help that would have been! Most of these plans are from individuals who have taken their time and energy to supply these plans for us. We thank them for their help.
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.
Are you building a homemade polyfim greenhouse, but are unsure about how to ventilate it? Here are a couple of solutions for you. You can see that this greenhouse has roll up sides, an option which is readily available, but can be costly. We have 2 options available that insert directly into your polyfilm covering without any additional framing. They use the channel base and wiggle wire to insert directly into the greenhouse covering. You simply cut the film and install these accessories directly into the film covering without any additional framing.
Intake Shutter with Solar Powered Opener
The first option is a solar powered greenhouse shutter. This has louvers and a wax cylinder powered opener. It will open when it is warm and close when it is cool automatically. They are available in 6 different sizes. If you would like to use this on another type of greenhouse such as polycarbonate, we can remove the base channel and you can insert this directly into a wood framed opening.
Solar Powered Roof Vent
The second way to do this is with a solar powered roof vent. This is a lightweight polycarbonate vent. It weighs less than 10 pounds, but you get all of the benefits of the durable polycarbonate covering. It also has the was cylinder powered opener that will automatically open and shut the vent as the temperature requires. To install this you simply cut the polyfilm and install it directly into the greenhouse covering.
A lot of people prefer to build their own greenhouses rather than purchase a kit. With these 2 ventilation options, there is no reason not to build your own polyfilm greenhouse.
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