18 More Tips for Greenhouse Structure Design

Features - Cultivation

Part II of a two-part special report. Industry experts share more insights into optimizing original and retrofitted greenhouse structures and systems, from lighting and blackout materials to improved sustainability.

April 18, 2017

An ArchSolar PV greenhouse facility conducting trials on PV shading levels and root zone heating. Many cannabis cultivators are looking at efficiencies and/or solutions from traditional agriculture, such as greenhouses, in launching or expanding their businesses.
Courtesy ArchSolar

In part one of this two-part special feature in Cannabis Business Times’ March issue, we reached out to experts in cannabis and greenhouse-related industries for their tips on optimizing greenhouse structures and systems. This second installment offers more insights on greenhouse options and technologies to help you make informed decisions to maximize your success when building a new greenhouse facility, as well as important questions to ask if you’re considering a retrofit.

Kurt Parbst

Kurt Parbst

Sales Manager-North America


Asheville, N.C.

1. Assess light penetration and blackout needs properly.

“In a greenhouse, you pull a blackout curtain to keep the extra light out after 12 hours. You need to have a blackout material that’s dark enough because the plant is quite sensitive to light pollution. You want a textile that is porous, so that any water that drips off the underside of the greenhouse roof can be taken up and humidity can permeate it. But since it’s porous, you can have light penetration through that.

“Some growers tend to shoot for darker-than-necessary conditions, and use three and sometimes four layers of a textile. Once you have three to four layers, it doesn’t have a good ability to breathe and allow humidity to permeate the membrane and escape the space. If you’re judging the light penetration of your blackout in the middle of the day, that’s not a good point. That’s not when you’re pulling it [to block out the light]. You generally pull the blackout after 12 hours, so it’s in the evening when outdoor light intensity is already quite low.

“Three to four layers also makes for a heavy, bulky installation that can be problematic. Maintenance over time will be a challenge because with all this bulk, you’re creating a lot of wear points on the wires and so forth that support it. In general, a high-quality, two-layer product is sufficient, provided it’s well-sealed around the perimeter.”

2. Understand appropriate lighting and improved technologies.

“Getting enough light is critical. With greenhouses in general, you can get about 75 percent of what the plant needs in terms of photosynthetic light from the sun. But light must be supplemented to receive sufficient daily light integral (DLI) if you want year-round, monthly production.

“… Once you’re pulling a curtain and you’ve got lighting underneath, it can create an overheating problem. Heat on the plant also creates transpiration, so that contributes to humidity problems.”

Parbst notes that there are lighting technologies available now that provide high light intensity with less heat.

3. Actively control humidity under the curtain.

“Once you close a curtain, you limit your ability to control humidity. Most plants are susceptible to being infected with fungal diseases if the conditions are correct for it, which means very, very high humidity. Fungal spores are in the [environment] all the time, entering that greenhouse. With trapped humidity in the space, you have a higher potential for disease.

“You need an active dehumidification [system] underneath the curtain in order to stay away from the high-humidity conditions that will [create an atmosphere ripe for] fungal diseases ... such as a desiccant system, so that you’re filtering the air though a desiccant dehumidifier and removing the moisture that’s trapped underneath the blackout curtain.”

Mauricio Manotas

Mauricio Manotas

President Ludvig Svensson Inc. Kinna, Sweden (corporate headquarters) and Charlotte, N.C.

4. Prioritize safety.

“There are a few, but very important considerations when choosing blackout or shade systems. The first one being the selection of a product that passes all the North American standards against fire. With [so] many motors and supplemental light fixtures, the growers need to rely on a product that is going to minimize the risk of a catastrophe or, if worst comes to worst, that will not create an issue with the insurance company afterward. I can’t tell you how many times some growers have ‘saved’ pennies to spend dollars on claims, fines or lost the crop to situations like this.”

5. Choose materials that are location-appropriate.

“Growers need to rely on companies that will select the right cloth for their operation; the requirements might not be the same in Washington as in Florida. Professional companies should offer this service [in helping to select the right materials] at no cost.”

6. Prioritize installation and proper sealing.

“The installation and seals of the light-dep are a key part of the success. You can have the best light-dep on the market, but with a poor installation, the light will come in anyway.”

7. Let your greenhouse “breathe.”

“[With] humidity management, growers are starting to realize little by little that installing products that don’t ‘breathe’ creates high humidity levels, opening the doors for fungus and diseases.”

Bob Rimol

Bob Rimol

Owner and Founder Rimol Greenhouse Systems Inc. Hooksett, N.H.

8. Be realistic in plans and expectations.

“Achieving optimal structural design for your cannabis cultivation greenhouse involves careful thought into where, when, how and why you’re using a greenhouse for your cannabis grow. One size does not fit all. Every project requires its own careful consideration, and what worked for one cannabis greenhouse setup may not work for another. Don’t make your build more complicated than it needs to be. Stay simple, stay focused and stay within your timeline so you don’t get bogged down in little details.

An Agam Ventilated Latent Heat Converter (VLHC) desiccant dehumidifier. BonarAgro’s Kurt Parbst says growers “need an active dehumidification [system] underneath the curtain in order to stay away from the high-humidity conditions.”
Courtesy BonarAgro

“Construction costs are often underestimated. Expect to face extremely strict requirements from building code officials that will result in higher overall costs. Timelines for construction must be realistic and attainable [given the many variables involved in individual projects].”

9. Stay flexible and adaptable.

“A cannabis greenhouse is a controlled environment, but never a perfect environment. This is especially true during certain times of the year and in certain locations in the country, including those that experience more extreme weather and temperature shifts.

“Expect to make changes and adjustments to your environment after you begin growing. Things change. Heating, cooling and environmental control requires a detailed, well thought-out plan. But be prepared to try new things; there are plenty of ways to get the harvest you’re hoping for.”

10. Know your space and its requirements.

“When it comes to actually building your cannabis greenhouse structure, it’s critical to know exactly what your grow space will require in terms of stability, environmental controls and protection from the wind and weather. Both freestanding and gutter-connected greenhouse styles work fine for cannabis production. Choose whichever style works best for your grow space.

“…. [Also], plan your greenhouse’s door locations for both security and material handling. You want an entrance that’s easy to access for you, but not for uninvited guests.”

Tony Kieffer

Tony Kieffer

Managing Director ArchSolar, LLC Portland, Maine

11. Investigate alternative heating technologies.

“How you engineer your greenhouse from a heating standpoint is significant. Radiant heat and even radiant heat in beds or in pots is something to look at. Depending on how you’re growing, even the root zone and the buds present a route to heat, versus heating air, and trying to heat the plant through the air.

“There’s also interesting work with establishing an earth-cooled greenhouse, using earth tubes. Corrugated earth tubes run down underneath and basically by day, take heat off of the ridge and bring it down through a series of tubes underneath the greenhouse, and transfer the heat into the ground. By the time the air comes out on the other end, it’s coming out at 55 degrees. That’s super easy to do at the time of greenhouse creation, in terms of excavation without a lot of capital equipment.”

Photos courtesy of Ludvig Svensson

12. Capitalize on what greenhouses do well.

“Humidity is definitely a challenge for the Northeast, as well as the Northwest and other parts [of the country]. Managing humidity in the greenhouse is different than managing humidity in an indoor grow. What you want to over-rely on in the greenhouse is air movement and air changeover, which you don’t necessarily have as much of in a big box building or a small indoor grow where space is at a premium, and air flow is not necessarily the first thing people thought of when laying those systems out.

“You want to design a greenhouse to take advantage of what greenhouses do well—and that’s being able to move that air and exhaust that air as your primary means to combat heat. There are a number of things that can be done in the Southwest with wet walls, [such as] evaporative cooling. That works where you have a dry climate, but it doesn’t work up here in the Northeast where it’s muggy when it’s hot.

“Also, make sure you’ve calculated for static pressure with your exhaust fans. People sometimes forget that with their light deprivation or breathable wall, and they lose some capacity in their fans. Therefore, they might have pockets in the greenhouse that aren’t getting the ventilation they need, and that’s where you can get tricky dead spots.”

Plants underneath Ludvig Svensson Obscura blackout climate screens. The company’s president, Mauricio Manotas, says that cultivators must choose a screen that is compliant with fire standards in North America. Manotas also says growers must choose a screen that is breathable to prevent moisture accumulation that can be damaging to cannabis.
Photos courtesy of Ludvig Svensson

13. Explore advances with solar technologies.

“In places where there is such a high level of sun that sun can be too much at times, solar panels can be incorporated into the actual glazing in parts of the greenhouse. Solar panels can be used up on the ridge of the [glazing] to provide shading and to generate electricity for the mechanical of the building.

“They’re relatively thin solar panels that cover thin bands on the ridge. It’s high enough on the greenhouse that it’s not blocking some of the lower incident light in the winter time, but it’s providing some shade while delivering electricity throughout the year. In places like the Southwest and in Colorado, depending on the market, [cultivators] might do well to think about that for vegetative crop areas. Nursery production space, with such large square footage, lends itself quite well to becoming a solar collector.”

Nic Easley

Nic Easley

Chief Executive Officer Comprehensive Cannabis Consulting (3C) Denver, Colo.

14. Don’t try to do it on your own.

“When it comes to choosing a greenhouse company or greenhouse design, you have to think about these operations as an organism. They have to be homeostatically balanced—maintaining a constant temperature, airflow, humidity, CO2 concentration, light penetration and concentration—in order to have a successful, functioning, living, breathing entity. If the space is sick, like a human being, you’re going to have problems.

A Rimol Greenhouse Systems greenhouse. Rimol owner and founder Bob Rimol cautions, “One size does not fit all. Every project requires its own careful consideration, and what worked for one cannabis greenhouse setup may not work for another.”
Courtesy Rimol Greenhouse Systems

“By focusing on the design and choosing a vendor that has good experience in greenhouse—hopefully from agriculture, but having then jumped into cannabis—you can design the building correctly from the beginning. You can design an organism that’s going to function instead of having catastrophic problems for life. Try to do it on your own, and it will be a sick building.

“All of those problems like mites, mold, mildew—everything requiring a really robust IPM or Integrated Pest Management plan—is a symptom of a much larger problem, with the root of the problem being that the building is a poorly designed organism.”