2/26/2015
The Science of Structures
Anne-Marie Hardie
So you’ve made the decision to build a new greenhouse. Budget is usually the first item that growers consider when determining the final design. But have you ever thought how the particular climate and crop can impact a greenhouse structure? Choosing the right design—one that fits both the needs of your region and crop—will help pave the way to a profitable business.
Pictured: The CS3 from Stuppy is a very versatile design that fits most geographic regions and building codes. It’s designed to be covered with a rigid covering, either 8MM twinwall polycarbonate, acrylic, corrugated polycarbonate or even corrugated metal.
It would be ideal to grow in an area where the climate closely matched the crop needs. If this were the case, growers would require few adaptations to their greenhouse structure. However, this isn’t the typical practice. Growers often have to adapt their greenhouse to meet the needs of the crops that will be grown. But where should the decision process begin? For Greg Ellis, Western States Sales Director for Nexus Corporation, growers should have their end goal at top of mind.
“When considering greenhouse design, begin with the end in mind, identify your market, the crop you’re going to grow and what you’re going to sell it for. And continue to work backwards and determine what the costs are to produce that crop,” said Greg. “The difference between your local climate and the condition that you will maintain in the greenhouse will drive what your costs are going to be. The bigger the difference, the higher your costs are.”
Justin Shelton, Regional Sales Manager for Stuppy Inc., agrees, emphasizing growers should review the full project—from their budget to future plans for growth—before determining the final greenhouse. Knowing the answers to the following key questions can help a grower streamline this decision process.
- Where will the greenhouse be located? Is it in a city? Country? What’s the landscape surrounding it?
- What are the climate variations in your region? Are you in an area of heavy snowfall, high wind or salt precipitation?
- What crop will be grown? And what are the crop’s needs in comparison to the climate in the region?
- How will the design meet the workflow needs of your growing operation?
One of the key areas to consider is the climate and weather pattern of your region.
“Climate is very important for a lot of reasons,” said Greg. “Your locale has its own distinct characteristics, from the level of light to the humidity level. Two different locations, each building a greenhouse, may address their local climate differently depending on what it throws at them.”
Greg provides the example of a Colorado grower where, despite it being quite cold in the winter, has very high light levels. This grower wanted to capitalize on the light to grow cut flowers, so the structure design included a glass covering, maximizing the light penetration, also able to withstand the cold winter climate. Conversely, a grower in Arizona may be trying to limit the light and sun to keep the greenhouse cool in the hotter times of the years. This grower may opt for a diffused poly or white polycarbonate to try to limit both the light and heat.
Does your covering meet the needs of your crop?
One of the first decisions growers make is choosing their greenhouse covering, whether it’s a polyethylene, glass or diffused covering. However, not all coverings are made for every area. For example, shared Justin, high wind areas would be best to steer away from double poly, and look for both a covering and structure known to withstand high winds.
The crop paired with the region will help determine the covering. For example, if the crop requires relatively low light, like foliage, than the grower may be fine using a diffused or shaded fabric. Conversely, states Greg, if a grower has a crop that has a high light requirement and is choosing to grow it in the North, then they’ll want to put on a covering that allows a high light penetration.
Thankfully, most manufacturers offer varying structural designs that will both meet a grower’s particular covering preference, as well as regional weather considerations, said Gary Baze of Rough Brothers.
Match your foundation to the elements
Snow load is often one factor that growers consider when determining structure, but wind can have an equally devastating impact. A reputable greenhouse company should ensure that the structure is able to hold up to the elements, whether it’s heavy snow or high winds.
“Ask any company scrambling to replace a greenhouse brought down by weather and they can tell you how detrimental an effect it can be,” said Gary. “Today, with all the expensive equipment and systems employed, it’s all the more reason why growers must erect a structure capable of protecting their investment.”
In areas where snow and ice are expected, steeper pitch roof profiles may be recommended to promote shedding. Growers in high wind areas may want to look at lower profile roofs to reduce the exposed area that the wind could catch, said Gary.
“Growers should look beyond what a manufacturer rates the structure for and ask hard questions about the design. From an engineering standpoint, we know that certain shapes used in greenhouse construction make a huge difference in whether a house will stand the test of bad weather,” he said.
Coastal recommendations: The impact of salt on structure
In the coastal regions, where high salt levels may be a concern, growers should look for noncorrosive hardware, said Justin. Making these simple changes and minor investments could help the grower save money in the long run. However, choosing the right design is only the first piece of the puzzle. Growers need to incorporate proper greenhouse practices to extend the overall life of their building. (Turn to page 58 for tips on how to extend the life of your greenhouse.)
Feeling hot
Southern regions with their high heat and light conditions come with their own set of challenges, particularly in the summer months. Growers that have moved to the south for the light, states Greg, may have to whitewash, employ shading systems and use either mechanical cooling or positive pressure systems to bring the light and heat level down in the summer. In these situations, he often recommends employing diffused coverings.
“Diffused covering not only makes the grower a better grower, it helps eliminate shadows, provides for more crop uniformity, actually institutes more breaks in your plant and takes the edge off of sunlight and heat,” said Greg.
When considering cooling, it’s important to review both the moisture and temperature level when the plants are growing. Plant transpiration can help reduce the overall temperature and increase the moisture level in the greenhouse.
With greenhouse structures, there really is no one-size-fits-all solution. What works well in Michigan, emphasizes Justin, may be too much for Texas. The weather of a region should be a primary consideration when designing a greenhouse from its foundation to the hardware.
“When it comes to structures, the lowest price doesn’t always equate out to the best value,” said Gary. “We all pay for steel by the pound. If one greenhouse is more expensive than another, check to see if there’s more or a different design of steel incorporated. It could very well make the difference between you sleeping comfortably through the evening or waking up to greenhouse alarms.”
Although cost will always come into play, a grower must consider whether the lower-priced structure is really a better value. Gary recommends that growers ask questions about the historical performance of a certain greenhouse design in the region before making that final commitment. By choosing the right greenhouse design, growers will ensure that their greenhouse will increase profit and not be a liability.
GT
Anne-Marie Hardie is a freelance writer/speaker from Barrie, Ontario, and part of the third generation of the family-owned garden center/wholesale business Bradford Greenhouses in Barrie/Bradford, Ontario.