Sealing your grow room is one of the most overlooked and yet, most important details to get right during construction or renovation of your facility. This holds true for all indoor cannabis cultivation facilities and climate controlled greenhouses for cannabis. I’ve been asked to solve for so many issues in a cannabis cultivation facility, whether it be lower than expected yield, lower than expected terpene content, the presence of microclimates or hot spots, unexplained temperature or humidity swings as shown in their data, an HVAC machine that can’t maintain the right setpoints, or repeated difficulty with aspergillus or another contaminant, especially microbials. It’s so often solved by taking a few days to seal the entire facility airtight. Why? I’ll explain more in detail, but first, let’s discuss why you should care.

Why you should care

Issues caused by a poorly sealed grow room typically go unnoticed and unaddressed for an extended period of time. It is often checked as a last resort after you’ve attempted to troubleshoot an issue and have eliminated everything else, and rightfully so. It does make sense to rule out other more direct causes first. By default, the determination typically must be reached by a process of elimination investigation. For example, if you’re having a temperature or humidity issue caused by an unsealed room, you’re likely to do the following and experience AT LEAST the resulting delays, but likely longer:

1. Comb over all of your data to see when things are going wrong – ½ day
2. Suspect equipment, call the HVAC technician & wait for them to arrive – 1 day
3. HVAC tech runs tests and determines the equipment is performing fine – 1 day
4. Team brainstorms to search for another solution – 1 day
5. Call a 2nd HVAC technician for another opinion – 2 days
6. HVAC tech #2 confirms equipment is working properly – 1 day
7. Call in the maintenance team to inspect the room where they find several holes in the walls and ceiling leading to leakage – 1 day
8. Maintenance gets supplies and seals the room – ½ day

By the time you’ve ruled everything else out, it’s determined that the room is not sealed properly. And by now your plants have been growing under suboptimal conditions for at least 8 days out of their 56 day cycle, for a total of at least 14% of their entire flowering cycle during a critical phase of growth. Instead of your room producing the expected 100 pounds of total crop this cycle, it’s likely to only produce 75-80 pounds because of this lost time. Those 20 lost pounds could equate to $20,000-$35,000 based upon your wholesale market price for flower in your state.

In speaking with a colleague, Jim Megerson, a mechanical engineer with Anvil Ag from Kansas City, he shared a recent story that resonated with me. A client reported they were having HVAC issues that turned out to be an improperly sealed grow room; the walls weren’t sealed to the floor, inexpensive and poorly sealed doors were used due to “supply chain issues,” and due to a local regulation the grow rooms opened directly to the outside environment. The issue took over 3 months to identify and another 2 months to rectify, totaling just shy of 6 months of suboptimal growing conditions. Even then, he said, had it not been for a cultivation director who was obsessed with monitoring his ideal vapor pressure deficit and a team of vendors, contractors and engineers who all put their heads together, it may have taken even longer to identify and solve the issue. This only proves that the 8 day example above is an extreme oversimplification and in reality, an unsealed grow room is likely to cause issues that will go unnoticed and unaddressed for months. 

In cannabis, every hour matters. While simplifying greatly, every hour that your plants are not living optimally causes a reduction in bud development, which ultimately leads to reduced yield and reduced potential revenue. At the end of the day, sealing your room is all about revenue and opportunity cost. 

The solution of sealing your room

Proper sealing of your rooms or sections requires the construction team or maintenance team to install tight seals around all doors, and to seal all penetrations into any walls, floors or ceilings using a zero-VOC polyether caulk or similar type product. It’s not recommended to use a standard type silicone in an operational grow room due to the VOCs it releases, however, it’s likely safe to use in a new build where there will be no plants for weeks or months. To take it a step further, I strongly suggest that you seal any and all conduit coming into the room as well. If there are any penetrations into your walls, seal it. It’s easiest to do this during new construction or a renovation, but this can be done at any time, ideally when plants are not in the room, to allow for maximal movement throughout the space. Have at least 2 employees work as a team to inspect every inch of every wall, ceiling, and floor in each room to determine where a penetration may exist. Mark them, then seal them. Always have at least 2 employees working in tandem, because humans miss things and 4 eyes are better than 2.

So what happens if we have leaks? 

Environmental Controls

If there are any unsealed cavities in your room, this creates the opportunity for air, moisture, and CO2 to leak out. As a result, you may not be able to maintain the appropriate daytime or, more commonly, night time temperatures that are ideal for your plant growth. For many years, growers have been most concerned with keeping their daytime temperatures low enough and maintaining enough cooling to combat the heat load put off by traditional HID or HPS lights. Now, with the mass adoption of LED lights, maintaining a daytime temperature has become less of an issue and instead maintaining the appropriate nighttime temperature has become the new challenge. In many instances we need to reheat the room overnight to maintain temperature.

Anytime moisture and heat have the chance to leak out of the room, it’s going to directly affect your relative humidity readings and your vapor pressure deficit (VPD). As HVAC equipment has become more advanced and we’ve been able to maintain a greater level of control over our rooms, maintaining enough moisture in the room for maximal flower growth has presented a large scope of intricacy and challenge as it is. If we have leaks, then the sensors that we have spread throughout our rooms and within our plant canopy aren’t providing accurate readings to signal to our equipment what to do and when to do it. 

With changes in both temperature and humidity, your vapor pressure deficit is altered. If the plant is not living in its ideal VPD, even for an hour, the plant will not be maximally transpiring and uptaking nutrients and will not be maximally growing; whether vegetatively or in flower. VPD is so vital, so we must maintain control over our environment to guarantee the plant is living exactly where it wants to be. 

Furthermore, when CO2 leaks out of the room, the CO2 controller will sense CO2 levels reducing and pump in more CO2 from your tank. CO2 has a cost, and while it may not be an expensive gas, letting it leak out into the atmosphere is literally leaking money. You will likely spend more on leaked CO2 over the course of one year than it will cost to seal your entire facility. We won’t address the potential environmental harm here, but there is a cost associated with that as well. 

For every hour the plant is not living in optimal conditions, yield suffers. Revenue declines. 

Equipment efficiency

When your equipment is getting mixed signals from your sensors because of leaks in the room, the machines will run through their cycles many more times and consume tremendously more power than they need to if the rooms are sealed properly. This inefficiency increases your operational costs, and is a huge waste of energy. It can also be damaging to the equipment and shorten the lifespan to have HVAC equipment continuously cycling on and off trying to maintain the setpoints that you have programmed them to achieve. If you’re investing hundreds of thousands of dollars to install the appropriate heating, cooling, and dehumidifying equipment, it makes logical sense to take the extra step of sealing your rooms so that the equipment can perform optimally and you can extract the maximal ROI from your investment.

Contamination risks

This next piece is a bit more obvious, but if you have air leaks in your grow rooms, you are inviting pests, mold, mildew, aspergillus, and all other types of pathogens into your rooms. Contamination of any kind dramatically increases the risks of crop disease, pest damage, and in the worst case, total crop failure. Let’s use another real example to illustrate this point. 

While this is important in every geographic region, I’m going to zone in on Nevada. Nevada is one state where you must test your flower for aspergillus. Aspergillus is airborne and it’s incredibly difficult to detect which strains are harmful since there are approximately 180 different strains of aspergillus, of which around 40 are known to be harmful to humans. The Nevada test is a simple pass/fail test, where if any one of four specific strains of aspergillus are found to be present, the entire batch fails. While we can test for the presence of aspergillus, testing for these exact four strains is not possible. Therefore, we must try to keep out all aspergillus. Since it’s commonly present indoors and outdoors, everywhere, the only way to prevent it from coming into the room is by sealing your rooms airtight. Ideally, our rooms are on a closed-loop HVAC system that utilizes UV lights to sanitize the air, so theoretically the air remains clean even as we enter and exit rooms since most of the air in the room stays in there, gets filtered, and recirculates. 

Let’s put this into revenue. Batch sizes in Nevada are 5 pounds and the fair market value (FMV) of flower in Nevada as of April 2023 is $1,944 per batch, making it worth around $9,720. Even if we don’t rely on the state’s reported FMV and look more realistically at what flower actually sells for, around $1,200 per pound, that’s $6,000 of lost revenue for each failed batch; which doesn’t include the sunk costs in materials and labor to grow the flower. Yes, there still is a market for failed flower in Nevada, but that’s not the ideal distribution strategy for any cultivator and may not even cover the costs to produce the flower indoors.

Crop quality and consistency & Revenue

All of the above – environmental control, equipment efficiency, and contamination risk all translate to one thing; crop quality and consistency and ultimately lost revenue. You will never be able to have a consistent crop harvest after harvest if your rooms are variable temperatures throughout their growing periods or if they are hotter in the summer and cooler in the winter because of all of the outside air coming in. Why not? Regardless of climate and geography, allowing external air into your grow rooms can cause issues that your equipment was not designed for and cause your flower to grow suboptimally. 

Since most rooms are designed for a specific heat load and moisture load, adding external sources of heat and moisture may challenge the HVAC equipment. Too much heat and moisture in a flower room often leads to mold, mildew, or the crop-killing botrytis, otherwise known as bud rot. 

As cannabis becomes ever more competitive, we need to push every edge we can. If our rooms are not the exact same vapor pressure deficit year round by maintaining the exact temperature and humidity each cultivar requires, they’re not growing optimally. If our plants aren’t growing optimally, then quality, consistency, yield and ultimately revenue will suffer. 

Odor control

Lastly, without a sealed room, the potential odor from flowering cannabis has the ability to escape your rooms and eventually escape your facility. In most states and countries, regulations require cannabis facilities to control their odor so as not to be a nuisance to neighbors. Without a sealed room, you open yourself up for potential liability and litigation. I’ve been asked to solve for cannabis odors in previous jobs and the single greatest impact we can have is to seal every room first and work your way out from there. Seal the grow rooms, seal the common areas, seal the exterior of the facility and then consider other options like supplementing a Febreze-like chemical to mitigate escaping odors if sealing the facility hasn’t stopped the odor issues. 

Additional helpful tips and suggestions

We’ve covered the reasons why we need to seal the grow rooms and many potential issues it creates as well as how to seal the grow room, and if you’ve read this far, I wanted to add more suggestions to help solve this problem before it creates issues for you. These have all come from my experience and the experiences of my colleagues: Jim Megerson of Anvil Ag, Rex Mustain of Associated Air Products, and Brad Marshall of  Zero Cool. Many items below are directed towards those facilities that are not yet operational or are still under construction, but items #3, #6, and #7 can be done in existing rooms to help highlight leaks in your room more effectively. 

1. Limit penetrations into your grow rooms in general. When possible, use wiring trays and/or conduit to run as many wires through an individual penetration as you can, which is easier to seal, rather than creating an individual penetration for each wire. The same goes for plumbing penetrations; if possible, reduce the number of pipes coming into the grow room and split them off once inside. 
2. Add a requirement into your MEP drawings that says something like, “Seal all mechanical, electrical, plumbing, fire protection and fertigation penetrations through all wall panels weathertight. Each trade is responsible for sealing both sides of penetrations weather tight using zero VOC and UV resistant caulking approved for exterior applications. Room shall maintain a weather tight and airtight construction in all spaces that contain plants and biomass.” This increases the accountability of your contractors to ensure they meet the standards you lay out and allows you to find the responsible party should you find a leak during commissioning or after construction is complete. 
3. Seal your insulated wall panels to the floor with an epoxy or epoxy-like floor coating by adding a seamless 4” cove molding from the floor onto the wall.
4. The grow rooms should be designed with positive pressure as compared to the interstitial space and hallways exterior to the grow rooms.
5. All measures should be taken so that no grow room should open directly to the outside environment. 
6. When ordering your new or upgraded HVAC equipment, ask the manufacturer to include a factory casing leakage test so that the equipment itself won’t be a source of leakage. 
7. Before moving plants into any room, a commissioning process should be conducted on all grow rooms, all HVAC equipment, and all ducting to ensure everything is airtight. This can be done right after construction is complete in new facilities and can also be done in between harvests in operational facilities. One tool to help with this would be something like BlowerDoor. There are alternatives out there to help with the entire room, the HVAC equipment and the ducting, but this should give you an idea to create your own solutions. 

I will acknowledge that it may seem trivial to some that I’m going to such great lengths to explain the importance of sealing your cannabis grow rooms, but it seems to be a pattern that people don’t realize or understand that a lack of sealing is so often the root cause. This has become one of the first things I check; in nearly every instance, the sealant, or lack thereof has been a primary cause of persistent control issues. While it may not be the only challenge your facility is facing, it’s a great place to start, and very inexpensive in the long run to take a few hours or few days, depending on the size of your facility, to do a full audit on what’s coming in or leaking out of your rooms.