Cannabis Greenhouse Construction Process

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Cannabis Greenhouse Construction Process

How to Build a Greenhouse for Cannabis Cultivation

The construction of your outdoor cannabis greenhouse can get complicated quickly, especially when there are many things to take into consideration before you can break ground. Add in the factor of managing multiple contractors and vendors, and the complications can compound. 

To build your cannabis greenhouse facility successfully, you’ll need to ensure that sure things are done right every step of the way—from site evaluation and compliance review to civil work and greenhouse construction. 

This chapter of the Ultimate Guide to Cannabis Cultivation will help you learn the key steps in building an outdoor cannabis greenhouse including site selection, compliance, build requirements, construction, infrastructure, physical building, and project completion. 

Table of Contents:

1. Architect, General Contractor, and MEP Selection

2. Greenhouse Site and Structure Selection

3. Laying the Foundation

4. Setting Columns and Trusses

5. Roof Coverings

6. Security Siding

7. Insect Exclusion

8. Greenhouse Construction Project Timeline

8. Building Department Inspections

Architect, General Contractor, and MEP Selection

Choosing the right people to help you build your cannabis greenhouse can make or break your project, so before you even begin to lay money down on your project, you’ll need to thoroughly vet your team. To begin your greenhouse construction process you’ll want to make sure you choose a contractor who suits your needs and who has experience in building cannabis greenhouses.  

A greenhouse itself is basically just a larger erector set; a skilled builder can build it based on the instructions that come with the greenhouse. However, it’s to your benefit to have a metal building contractor work on your project because they will be more familiar with the style of construction.  

The architect typically will coordinate the different engineers* required for the project; oftentimes if you go to a local architect, they’ll have a group of people they like to work with who cover soil tests, foundations, and civil work. Your ideal architect would be accustomed to taking all those different inputs and putting it all together into what is called a design review pack for the building department. 

Prospiant works within that whole subset of groups who work with the architect, and we provide the structural information for the architect to build their design review package. The architect is also going to be familiar with different code compliances that they need to know about, such as fire suppression, occupancy level, and ADA accessibility for handicapped accessibility.  

A general contractor can do a lot of the same work as the architect but typically works outside of the architect and coordinates the various tradespeople.  

One of the last steps in this initial build planning process is to have the MEP (mechanical, electrician, plumber) come in and sign off on all the different pieces of equipment such as plumbing, electrical, and gas lines.  

You can choose any general contractor but building experience with home or office construction does not necessarily translate to greenhouse success! 

Someone who knows the tricks of the trade for building greenhouses has cannabis industry-specific experience with critical aspects such as the light deprivation system and how the flashing is added to the construction.  

For example, an experienced greenhouse builder may want to put the flashing on the trusses before lifting the trusses into place, saving time and money. You are going to have a shorter build time with a good greenhouse builder. 

Additionally, a cannabis-industry experienced architect will be familiar with cannabis cultivation processes and structures. This will be to your advantage because the architect can do the layout of the greenhouse (or indoor grow warehouse) and they’ll be familiar with the types of equipment that you’ll need and the processes that will take place in your head-house or cannabis processing building.  

Greenhouse Site and Structure Selection

Figuring out what kind of greenhouse structure you’ll need is critically dependent on your geographic location, its climate, and seismic activity. A site evaluation will help you determine whether your indoor grow facility or greenhouse structure can fit on the site.  

As part of the evaluation process, you should also identify space for future expansion and other facilities you might need. Environmental elements of your site, like soil composition and terrain, should also be studied before construction takes place. 

Site Selection: Critical Considerations

First, find out if your local government has a pro-cannabis mindset with the local municipality. It sounds obvious but determining the legality and philosophy of the city/county government towards cannabis cultivation is the most critical step before taking any action towards construction.  

Checklist of questions to consider:  

  • Does the city or county permit, or even promote legal growing? 
  • Is the cannabis greenhouse approval process streamlined? 
  • How close is your site to highways and major distribution pathways? Cannabis cultivation is labor-intensive so it’s important that the construction crew—and eventually your workers—can easily get to your site.  
  • What is the local climate? How much rainfall? What kind of wind does the site get? What are the snow loads? Amount of sunlight? 
  • PRO TIP: Always select a sunnier site, an area that gets lots of sunlight. 

You may want to get away from general population areas, but you’ll need to take into consideration all the elements above. Land price might be cheaper, but your operational costs, utilities, and transportation will be higher. 

Load Reviews: Choosing your Greenhouse Type

Load reviews are going to cover the different things that are going to happen to your greenhouse structure based upon where its located. This includes everything from wind loads, snow loads, and seismic loads.  

These loading aspects will vary from site to site; when  selecting your structure it’s important to consider what the design of your structure is going to have to withstand. For example, if you’re in a very heavy snow load area you’re probably not going to want to choose a structure that has, say, a double poly-roll plastic roof. Rather, you’re going to want a structure with an A-frame and a hard, rigid covering that can really stand up to the snow loads. The same thing applies to wind and seismic levels; these are considered live loads.  

But we also must consider dead loads too, such as light and heating and cooling equipment and shade systems. Cheaper structures, for example bent tubing for a high-tunnel structure, probably won’t be able to pass any kind of code for supporting the different lead loads inside the greenhouse.  

The live and dead loads all need to be taken into consideration when choosing a specifically engineered* structure to take on those types of forces.  

Typically, greenhouse engineers* will tighten the truss spacing to manage the varied wind and snow amount. Instead of having a 12-foot truss you may have a 10- or 8-foot truss to withstand different loads.

Reaction Loads

Reaction loads are facing loads against a column which are used in conjunction with soil tests. Reaction loads are things like; how hard does the wind blow? How hard does the snow fall against? What kind of stresses does that create where the column is anchored into your foundation?  

Prospiant will provide calculations for all these loads, that in conjunction with your soil engineer’s* test will then go to create your foundation inside. We can build our structures to meet any specific loads, meaning we can put these structures anywhere in the United States or Canada and we can meet any load requirements that are out there. 

Laying the Foundation

The foundation of your greenhouse is usually cement but can be other surfaces such as rocks, gravel, or a ground cover cloth, but we do recommend concrete because it’s much easier to work with. When you’re building a foundation you’ve got your columns on top of it, and your trusses go on top of those.  

Using a concrete slab as the foundation of your greenhouse increases greenhouse cleanliness, reduces humidity, and enables better transportation of growing equipment and the crop. Concrete slabs will have higher costs yet contain substantial benefits.  

In preparation for laying the foundation, your architect will take the abovementioned reaction loads along with the soil test (to measure soil compaction) and the geotechnical engineer* will design the foundation for the structure.  

After this has been completed, the architect will typically lay in the foundation design on top of the Prospiant structural designs and create a unique architectural layout which will then be submitted to the city for review and approval.  

When it comes to laying the foundation, concrete slabs are most commonly used in a high-end cannabis greenhouse. Concrete increases your cleanliness because it’s much easier to keep the foundation clean, as there is less surface area versus a rock substrate or any type of ground cloth cover. Less surface area equals fewer pathogens, fewer places for mold spores, and less places for bugs to populate. A concrete slab also reduces humidity as it’s easier to keep dry because it is typically built with floor drains. 

Concrete also makes it easier to work on, allowing better movement of growing equipment and making it easier to harvest crops as you’re moving it through your greenhouse. Although concrete slabs have a higher cost, ultimately, they do deliver substantial benefits. However, they are much easier to put in during the initial install of a greenhouse versus a retrofit of a greenhouse or indoor grow space.

Setting Columns and Trusses

After your concrete slab has been poured, it’s time to set columns and trusses. Prospiant greenhouses use pre-manufactured trusses to support the roof. Prefabricated trusses are built in a manufacturing facility and are carefully designed to carry the load of a roof to the outside walls.  

The primary benefits of using prefabricated trusses are cost savings, construction speed, consistency, and strength. While the basic advantages are mentioned above, additional advantages of roof trusses in building greenhouses include: 

  • The use of professional design and fabrication techniques. A trussed roof system is designed by engineers to accommodate the specific roof design and meet building codes to enable more uniform sizes and roof pitches.  
  • Roof trusses span much longer distances without the need for load-bearing interior walls. 

Roof Coverings

Standard greenhouse coverings are high light transmitting materials. The use of natural light through these coverings is a tremendous cost savings versus indoor growing facilities and their use of high intensity growing lights. In addition, greenhouse coverings have various characteristics that enhance the growing environment. For example, some coverings will diffuse the light by giving a more uniform and deeper light penetration.  

Polycarbonate structured sheets, either in multi-wall or corrugated configurations, are common in the cannabis market. The multi-wall sheets give the user energy savings over single-wall polycarbonate, while the single-wall covering will have a higher light transmission for the plant. Both types of sheets can be manufactured with light-diffusing abilities.  

The use of metal and insulation in the walls increases energy savings, lowers operating costs, and improves the overall growing environment. This covering is particularly advantageous in the roof and walls for the work areas of the operation.  

Glass is a traditional greenhouse covering that is still used in today’s market. Current glass products allow for wider bar spacing, yet still withstand required snow and wind loading. The styles of glass used include tempered and laminated. Glass attributes are high light transmission and longevity. Glass, as a single layer covering, has higher energy costs and heat gain that can be partially offset with energy curtain systems. 

Security Siding

By growing cannabis in a greenhouse, there are often concerns about security. With traditional glass or polycarbonate sidewalls, visibility from the outside, theft and the loss of confidential growing practices are at risk. To remedy this situation, hybrid greenhouses have insulated metal sidewalls to add a solid layer of extra security. When growers choose not to have outdoor signage, then the internal contents of the greenhouse will remain unknown. From an outside perspective, observers will simply see industrial building structures. The addition of insulation provides further energy consumption savings. Metal siding is also part of the light deprivation system. Traditional greenhouse coverings need to be covered during dark photoperiod time frames. These systems provide an added cost and will need to have maintenance. There is an added benefit of the interior metal reflecting light back to the crop. 

Insect Exclusion

Growing cannabis in an organic environment without the use of pesticides and fungicides is important for consumer health. Unless protected, greenhouses are at risk for an infestation from the outside environment. To reduce the use of chemical insecticides and pesticides, screening is the most effective and economical strategy available.  

While screening does not guarantee a completely pest-free greenhouse, it makes a major difference. Using screens over greenhouse vent inlets can be tricky due to airflow requirements inside the greenhouse. Screens create resistance, which reduce airflow and affect the operation of the cooling/ventilation system. When the mesh openings in the screen are larger, there is less resistance.  

Appropriately matching the mesh type to the pests that you are trying to exclude is important. Maximizing the screen hole size allows the ventilation system to work more efficiently. The greenhouse design team needs to consider these factors when professionally designing the ventilation equipment. 

Buildout Steps Summary

Not always in this order but this is a typical buildout process:

  1. Drawing up plans and submission for approval 
  1. Site Preparation – Utilities, Grading, Soil Tests 
  1. Foundation and Flooring 
  1. Setting Columns and Trusses 
  1. Purlins and Wall Framing 
  1. Roof, Coverings, Curtains 
  1. Equipment Installation <LINK to Equipment Chapter 5b!> 
  1. Electrical, Plumbing, and Water Connections 
  1. Final Inspections 

Greenhouse Construction Project Timeline

Typical 20-Week Build Schedule*

  • 1-2 weeks for proposal design 
  • 3-4 weeks for engineered* drawings 
  • 4-6 weeks for production and delivery 
  • 7-8 weeks for construction 

*Contractor schedule can vary due to size of project, location, and scope of greenhouse equipment.  

A basic timeline for a greenhouse build can vary a little bit depending on several factors. However, typically allow for 1-2 weeks for design work to produce what we call a proposal design. This is when we meet with you and determine what it is that you would like to design and what type of structure is needed for your location, and what your specific requirements may be.  

Then we have about 3-4weeks for commissioning the engineer* drawings wherein our engineers* draw the plans you will need to take to your building department for approval. The engineer’s* drawings are also needed for bidding as well as building your project.  

The next step we are looking at is 4-6 weeks (about 1 and a half months) for production and delivery. Once your plans have been approved by the building department, you come back to us and say okay, we are ready to go to production!   

As soon as we go to production it could be anywhere from 4-6 weeks (about 1 and a half months). If it is a significantly large project, then it might take 6-8 weeks or even longer. It all depends on the size of your facility, but 4-6 weeks is normal.  

The 6–8-week timeline for construction is completely dependent upon the size of your structure, who you are using for your general contractor to put the structure up, and any other variables such as labor staffing or weather.  

The caveat here is contractor schedule can vary due to size of the project location and scope of equipment. But this is a basic project timeline. As a rule of thumb, you can estimate a minimum of 3 to 5 months from the start of the project to completing your project, again, depending on the scale of your greenhouse project.  

Building Department Inspections

Your local Building Department will have specific steps to go through and these will vary depending on your state, county, or city. The following is a general overview of the type of building inspections you’ll have to move through for your new greenhouse.  

Plan Approval: Once you have engineered* plans drawn, you’re going to submit those to the building department who will review them and approve or recommend changes. Typically, these changes may be along the lines of adding some doors or some fire suppression.  

Structural Inspections: After plan approval, structural inspections will include a foundation inspection, as well as mechanical, electrical, and plumbing inspections. 

These various inspections throughout your construction process will culminate in your final building inspection which is where you obtain your Certificate of Occupancy otherwise known as your C.O. 

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