7 Things to Know Before Building a Greenhouse


Wouldn’t it be amazing to grow tasty big tomatoes all year round for perfect BLT’s or pick bright, cheerful flowers even on the dreariest days?

Gardening enthusiasts can have these things and more by constructing a greenhouse in their backyards or acreages. You can choose a mini greenhouse, small greenhouse or even a barn greenhouse for whatever purposes you need it for. But there are some things you should know before even starting to find greenhouse plans or choosing a DIY greenhouse. And if you just want someone else to build it for you, there are plenty of companies all types of greenhouses they build to suit your wishes.

Here are seven things to think before plunging ahead with your own greenhouse:

1. Your Reasons to Build One

Zack Clewer, who is Janco’s sales manager, says that most of their clients want a greenhouse because gardening is top of favorite hobbies in the world. But the company also builds conservatory structures, which are designed as full enclosures, so people can use them for hot tub rooms, dining areas or just an additional living area. One client bought a greenhouse because he wanted a room attached to his house in the Smoke Mountains where he could simply smoke cigars. Vents at the top of the structure allow all the smells and smoke to rise out without leaving any unpleasant after-odor.

Popular reasons to build a greenhouse or conservatory: 

  • All season gardening – you don’t have to worry about growing vegetables in winter, the controlled environment inside the greenhouse helps everything thrive despite the cold outside.
  • The perfect environment for growing basically everything – from herbs to flowers and vegetables, the greenhouse environment secures enough heat and water vapors to make greenery thrive. 
  • Money-saving – many households spend a fortune on plants and lawn grass for their outdoor gardens each and every spring season. When you have a conservatory, you can grow as many seeds as you want, and you’ll probably have more than enough to give away to friends and family as well.
  • Space with many purposes – when you have a greenhouse, you won’t even need a garden shed because you’ll have enough space to store tools and other equipment.
  • Plant protection – plants which grow in greenhouses are protected from unpleasant weather, pest infestations such as caterpillars, spider mites, locust swarms, and a many other. Overall, plants that grow in conservatories are healthier.

2. Cost

Do you want to make a big investment or a small contribution in this greenhouse design? Do you want to do it all yourself, buy a greenhouse kit with all the building materials, or have someone else build it for you with the greenhouse design you chose? All of these decisions will alter the price.

The national average for a 12-by-12-foot building at $25 per square foot would cost $3,590, according to Fixr and the Craftsman National Building Cost Estimator. Make sure to get at least three different contractor bids and quotes for the work. Each bid should include everything — from site preparation to water supplies to finishing work.

If you want to have concrete as your flooring, that will cost with labor about $540. If you need to add heat before of freezing weather and you plan on using it year-round., electric or propane heaters will be required. Fixr says the average price for a unit to meet the needs of this size of greenhouse will be $250.

You can also buy DIY kits online and at businesses that sell these products. For instance, Walmart offers an aluminum-frame, 8-by-8-foot structure for $2,114 with a $100 freight delivery. It has polycarbonate panels with an aluminum frame, which the store says are virtually unbreakable and block 99.9% of UV rays. You can also find free greenhouse plans, tutorials and YouTube videos online if you want to build it all by yourself ground up.

You might want to consider even building a larger greenhouse — more than 300 square feet — because the cost is less per square foot of usable space than smaller ones, according to the Oklahoma Cooperative Extension Service. But remember that they will cost more initially and cost more to run.

3. Style of Greenhouse

Choosing the style of greenhouse has a lot to do with what kind of backyard greenhouse projects you plan on doing now and in the future, such as growing enough veggies or flowers to sell at a farmer’s market. You also should consider what other style of buildings are located on the proposed site.
Here are a two types of greenhouse structures to think about:

Attached Lean-to

This greenhouse is built against an existing structure on one or more of its sides. It can be attached to the house or other buildings, says the Oklahoma Extension.


It’s a separate building. It is usually situated near the outdoor garden.

About 50 percent of customers of Janco Greenhouses in Georgetown, S.C., choose standalone greenhouses and the other 50 percent want the attached lean-to option.

“Some people want to come and go into their conservatories from inside their homes,” says Zack Clewer. “Some want that standalone greenhouse near their outdoor garden.” 

According to Jane Wilson, a professional from FantasticCleaners.com.au, there are multiple DIY options for you to choose from when it comes to glass greenhouse design. Some of the most interesting the company had to clean are:

DIY Window Greenhouse

A great DIY solution for dealing with old and unwanted windows is to use them to build a greenhouse. Such spaces are perfect for growing herbs and small plants, as windows are usually designed for maximum light penetration. 

Also, you can easily design your window greenhouse to open on both ends, which ensures good air ventilation. The only obstacle you need to look out for is water runoff. You need to calculate the slope and the amount of water used precisely to avoid water stagnation. Otherwise, it can lead to mold, mosquitoes and other issues. 

Tabletop Greenhouse

This is a very simple and DIY type of greenhouse. It is the perfect project for anyone who feels particularly crafty, or if you want to grow plants in a well-protected environment. Tabletop greenhouse design is unique, personal, and depends on your imagination. 

You can build these out of old picture frames, fish bowls and other glass materials you have to lie around.

4. Walls and Windows

Pre-treated wood, aluminum, steel or even old windows can be used to build a greenhouse frame. The materials you use on that frame can vary, too. You can use old glass windows or glass picked up from a flea market or recycling center. But polyethylene has become something of a standard. Clewer adds that all of Janco’s greenhouses are made of aluminum because it doesn’t rust or rot. It should last forever.
As for the walls of the greenhouse, you can choose fiberglass, clear plastic sheeting, polycarbonate, old windows or glass. Clower says Janco offers many glazing options for the glass such as insulated glass or a glazing that helps retain the heat. Companies also sell heat retention curtains for greenhouses.

5. Air Circulation

Automatic vent openers are a must. They prevent greenhouses from overheating — plus, the breeze is free, says Clewer. He also suggests oscillating fans used year-round but mostly is essential in the cold months to prevent dead zones. You can also get everything in the greenhouse automated, including the fans, heat, cooling, and irrigation in case you go on vacation, Clewer adds.

6. Permits Needed

If you need a building permit to build or place a greenhouse on your property, it really depends on the location of where you live, Clewer says. For most rural areas, it’s like adding a shed, which is an auxiliary building and you don’t need a permit. However, he has found that the closer you get to a big city, the tougher the codes are. Those jurisdictions are more likely to require a permit. Local building authorities have the final say on whether you need a permit, so check with your local planning department.

7. Strength Against Weather

If you live in an area susceptible to wind or storms, having a greenhouse anchored to a foundation with a strong structure can prevent from it blowing away. Those anchored to heavy-duty footers are like building a home: It isn’t going anywhere. You might break some of the glass, but those are replaceable.

You can also save money and build your own greenhouse with barn boards, PVC pipes, old windows or plastic sheeting for a DIY project. There are plenty of free plans for greenhouse designs online. Just be aware that you need some know-how and lots of hours to put it all together. Also, if the greenhouse frame isn’t sturdy enough to withstand a storm, high winds or the weight of snow, then all your time was wasted when it collapses or blows away.
You need to think about where the morning sun rises so you can figure sun exposure, what type of greenhouse projects you plan on doing, how much shelving you will need to grow your plants, and whether plastic sheeting or actual glass would be best for your purposes.

Clewer emphasizes that if you have a green thumb, you can grow anything in a greenhouse. He has a client in Maryland who bought a couple of greenhouses to grow an unlikely plant in a four-season climate: palm trees.
“He loves palm trees. So, he grows them and keeps them growing through the colder months. Then, he rolls them out to his pool area in the summer,” he says.

Main image credit: jermudgeonCC BY-SA 2.0 

Lee Nelson

Lee Nelson

Lee Nelson, an experienced freelance writer and former award-winning newspaper reporter, writes for National Association of Realtors and many state Realtor magazines. She lives in Illinois with her high school sweetheart and loves cooking, swimming, traveling and spending time with her grandchildren.