When deciding how to build a greenhouse you have multiple decisions to make. I will list them first for you and then explore them all in more detail. The list is not necessarily in the order of importance for everyone, as we all have our own priorities.
1)What will the cost be?
2)Where will you locate it?
5)What type of foundation or base will you use?
6)Are your utilities close by?
7)How will you use the greenhouse? Will you be using it year round or just seasonally?
8)What size will you need?
9)Do you need a portable greenhouse or permanent structure?
10) Do you need a building permit?
11) Do you have an HOA you need to check with?
12) How will you set up the interior? What type of greenhouse base or floor will you be using? Will you be using benches or placing larger plants on the floor?
13) Will you need a greenhouse ventilation system?
14) Will you need a heating system?
15) Will you try to automate some of the systems?
16) Are you going to use a greenhouse kit, or are you going to designing your own structure?
Deciding How to Build A Greenhouse
Now let’s break these down and explore them further.
1). What will the cost be? The cost can vary substantially going from around $100 for a temporary greenhouse to $10,000 for an orchid greenhouse to hundreds of thousands of dollars for a commercial greenhouse. Most backyard greenhouses will run in the range of $800 to $20,000. Again, this depends on the materials you are using. It is best to set a budget you feel comfortable with, see if you can build the greenhouse you want, and then adjust from there.
2). Where will you locate it? Will this be freestanding or an attached greenhouse? For an attached greenhouse you do not usually have as much selection, you are basically limited by the location of the wall you want to attach to. You should place this in an area with at least 6 hours of sunlight. If you do not have such a location you can always add supplemental lighting. But, this is an added expense that most of us choose to avoid. You should use a north/south orientation unless you plan on using solar practices. For solar greenhouses the long side should be facing to the South. Most people will build a long sloping wall for this to maximize the sunlight. It is best to face the door end away from the prevailing wind to help avoid heat loss. The placement should be to the south or south east of your home or building. The North side is the worst choice. Be sure to look at your trees and structures and make sure that none of them will be casting shadows on your building.
3).What type of structure will you build? Oh, there are so many choices here, all with different benefits. You can build a beautiful victorian greenhouse with an entryway built off one side, you can build a curved eave polyfilm covered greenhouse, a lean to or attached greenhouse, a geodesic dome, an A frame, the possibilities are endless. On a lot of these configurations the only difference is the looks and the cost. Some types of greenhouse, like the Chinese style greenhouse are performance based.
4)What type of greenhouse glazing material will you use? There are a lot of options here. Just be sure whatever you choose that it is UV protected (with the exception of glass). If only one side of the material is UV protected (such as polycarbonate greenhouse panels) make sure you put the UV protected side to the sun. This will ensure that your sheets will perform to their capabilities. A lot of people will go to a local store and buy whatever film is on the shelf. This is typically not UV protected and will last only one year at best. The most often used greenhouse film is 6 mil, 4 year. What that means is that the material is 6 mil thick and the UV protection is rated to last for 4 years. The risk with film is that you may get a tear. There are reinforced polyfilms available that have a rip stop feature. Of course glass is the timeless beauty when it comes to a greenhouse cover. Please be sure to use tempered glass for safety reasons. Actually according to building codes any glass next to a door or within 18″ of the ground must be tempered. Also, it is not a good idea to have regular float glass above your head in the roof.
5)What type of foundation or base will you use? There is usually confusion over the terms foundation and base when building your own greenhouse. A lot of the greenhouse kits for sale will have an optional base available. These are just around the perimeter of the greenhouse. A lot of people think this will included a floor, but it does not. The purpose of this is twofold. First you attach the greenhouse to the base and you secure the base to the ground. Therefore the base is acting as an anchor system. The second reason is that some of the kits need this lift off the ground in order for their doors to function properly. This is a great way to secure a small greenhouse. If you get into larger greenhouses or glass greenhouses you should be building a foundation. This should follow the same building guidelines as if you were building a garage, a shed, etc. You should be sure to have a footer that is deep enough to be below your frost line. This is to avoid any damage to the greenhouse during the freeze / thaw cycle. If you are not sure what your local requirements are you can check with a local contractor or your building permit office.
6)Are your utilities close by? Don’t forget this one. You will need electricity and water to operate your greenhouse. You may want to use natural gas or propane for the heater. Just be sure that you are able to bring these utilities to the greenhouse without too much trouble. After all, no one wants to drag a hose across the yard every day. Sorry, that is a personal issue.
7)How will you use the greenhouse? Are you going to use it year round? Are you growing crops to sell, or just for your own family. Maybe you are housing your prize orchid collection here. Some people only use their greenhouse to over winter plants and to start seedlings. This will help determine the answer to some of the other questions like size and budget.
8) What size will you need? The saying goes that when you buy your greenhouse you should always go one size up from the size you think you need. There are several reasons for this. We are all collectors and have a tendency to pick up an unexpected plant here or there. If you are growing food you may want to experiment with different crops. If you are overwintering your plants I suggest setting them in the yard in a configuration you think would be acceptable inside your structure and measuring around them. You can use graph paper to design your benches and systems.
9) Do you need a portable greenhouse or permanent structure? There could be multiple reasons for using a portable greenhouse. Maybe you are planning on moving in the near future. Maybe you just want to get your feet wet and give it a try. Maybe your neighborhood will not permit a permanent structure. A permanent structure will often require a permit. I will go into that in more detail in the next question.
10) Do you need a building permit? Many dealers will tell you that if you buy a greenhouse under 120 square feet that you will not need a permit. I know for a fact that is not always true. We are required to get a building permit for anything over 100 square feet. The best bet on this is to check with your building permit department. If you are putting up a portable greenhouse the chances are that you will not need a permit. But, if you are building a walk in greenhouse that requires a foundation you will probably need a permit. Best practice is to check locally.
11) Do you have an HOA you need to check with? This is one a lot of people forget to check on. I had one customer who had his greenhouse entirely installed when the HOA came along and made him remove it. That one hurt. Check first.
12) How will you set up the interior? What type of greenhouse base or floor will you be using? Will you be using greenhouse benches or placing larger plants on the floor? This kind of goes along with the step of figuring what size backyard greenhouse you will need. We do not recommend using a bench over 3′ wide. It is impossible to reach to the plants in the back if you go any larger. If you are using a bench down a center walkway you can use up to a 4′ wide bench as you will be able to reach from both sides. You may want to place larger plants in pots on the floor on one side and benching on the other side. For the floor you can use several options. If you are choosing concrete be sure to pour it so that you have drainage with a drain placed right into the concrete. You can use ground cover with sand, pavers, gravel over top of it. You can make walkways down the center with decorative pavers. There is no right or wrong here, just make sure you have addressed keeping weeds out and drainage.
13) Will you need a greenhouse ventilation system? A lot of people think this is not necessary. A greenhouse can heat up quite quickly with a bright sun. I have seen a 60 degree sunny spring day where my greenhouse fans will be running. I keep my thermostat set at 90 degrees. This system is set up with an exhaust fan that is typically placed up high in one wall, one or two intake shutters placed down low on the opposite wall and a thermostat. You should also have circulating fans which are set at a slow speed. They will greatly increase the health of your plants. Greenhouse vents in the roof are also an easy way to get some of the heat to escape. Warm air will rise, so if your roof vents are open, it will escape that way.
14) Will you need a heating system? Greenhouse heaters are available in electric, natural gas or propane. Do not put any electric heaters where they will get sprayed with water. Some of the natural gas or propane heaters are set up to be placed on the floor. There are also hanging heaters in electric, natural gas and propane. Overnight a greenhouse will lose almost all of the heat it gained during the day. So don’t count on that. There are some solar practices which will help to keep the heat from the day in to a certain extent, but they should never be counted on as the sole source of heat.
15) Will you try to automate some of the systems? It certainly is nice to have some automated systems. In a hobby greenhouse the ventilation system will typically be set on a thermostat. Roof and side vents can be fitted with solar powered openers. These are a wax cylinder that is based on expansion and contraction. When the wax gets warm it expands and pushes the vent open, when it cools it contracts and pulls the vent shut. There are certain things like lights that can be put on timers. Some think that they need an entire greenhouse control system. These are quite expensive and generally only used by commercial greenhouses.
16) Are you going to use a greenhouse kit, or are you going to designing your own structure? Will you use free greenhouse plans or enlist the assistance of an architect? There are a lot of possibilities here. You may have an odd shaped location in mind for your greenhouse. Some manufacturers are able to customize this for you. Other times it will serve you best to design and build this yourself. Of course another issue to consider here is time and cost. Many times the manufactured greenhouse kits will go together much faster than a greenhouse you are building yourself. But, there may be a substantial cost difference, especially if you are getting into custom construction. Check on pricing and options before making this decision.
Planning how to build a greenhouse may seem like a daunting task, but if you take these considerations one by one you will have a pretty good idea of where to start with this. Of course don’t forget to contact a professional representative to discuss these options further.