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Cleaning Up a Cannabis Grow Operation

by / Thursday, 15 November 2018 / Published in Environmental Testing, Healthy Building Inspections & Testing
How to Clean Up a Weed Grow Operation

With the legalization of marijuana, some black-market growers are abandoning their illegal cannabis grow operations. Grow ops, often set up in rented properties, can leave a mess for landlords to clean up. Many of these properties are also put up for sale and then become the responsibility of the homebuyer. Identifying a grow-op is often not that difficult because of the distinctive and lingering odor. However, eliminating that odor and identifying other potentially dangerous issues and modifications is another matter.

Common Grow-Op modifications

Ventilation crudely roughed-in and installed through siding.

Modifications to ventilation, air conditioning, electrical, and water lines are common in indoor cannabis grow operations.

Growing plants indoors creates high humidity that needs to be expelled. Different approaches to this could involve splicing into existing household ductwork. New ductwork could also be “installed” by cutting holes in the building to exhaust to the exterior, or worse, exhausting to somewhere else inside the structure. Exhaust ducted into attic, crawlspace, or wall cavities can lead to mold problems and potentially structural damage.

Holes created in the building envelope for ventilation may not be weather tight which could allow rainwater or pests access.

The high electricity demands of grow-ops may lead to unsafe electrical modifications.  Electrical generators may also be used to meet the demand. In this case, diesel contamination may exist on site.

The use of pesticides and fungicides can also lead to site contamination. Pesticide residues can remain on surfaces. Pesticides could also be spilled or disposed of on site. There may be soil contamination or pesticide-soaked building materials from any spills that occurred. Surface or soil lab sampling may be necessary to determine the extent of the contamination.

Another potential hazard is that the property was also used for the manufacture of other drugs, such as methamphetamines. Contaminants from meth pose a health hazard for those performing the cleanup if they aren’t properly protected.

Outbuilding used for a grow op is fed with a 200-amp service and a vent through the exterior wall that now houses birds.

How to clean up a cannabis grow-op

  • Establish if the site is also contaminated by manufacture of other drugs. Surface sampling may be necessary.
  • Hire a licensed electrician to inspect and repair unsafe electrical modifications.
  • Hire a licensed mechanical contractor to inspect and repair modifications to the household HVAC ducting.
  • Inspect for mold and moisture related damage to the structure. These can occur from excess humidity, from leaks in irrigation lines, or from moisture intrusion through poorly installed ventilation.
  • Test for pesticide residues or other contaminants, such as spilled fuel.
  • Remove all water damaged materials such as subfloor.
  • Remove residues from surfaces that harbor odors. Fatty terpenes are responsible for the odors and they are very sticky and difficult to remove. You’ll need to clean all surfaces with soap. The surfactants in the soap can cut through the terpenes. Porous surfaces will be more difficult, if not impossible, to clean and may need to be discarded.
  • Presence of extensive interior mold may require professional mold remediation.

In Canada where growing plants for personal use indoors is now legal, real estate agents have recognized the risks to property associated with indoor grow-ops. The Ontario Real Estate Association (OREA) has developed a five-point plan for the impacted properties with the goal of making buildings safe for homeownership and for homebuyers.

Among their recommendations is to inspect illegal grow operations and determine what actions are required to make it safe. OREA also recommend that all licensed home inspectors are required to have training on how to spot the signs of a former marijuana grow-op.

Cleaning Up a Cannabis Grow Operation

Hole cut through subfloor leads directly to crawlspace.  Discarded wood from the modification dumped there can attract mold and termites. Also, note the rotting subfloor.


Ontario Real Estate Association 5-point plan

Five Point Plan

We are experienced in working with growers and building owners to address environmental concerns. Some want to optimize growing conditions, and others want to rid the building of all evidence and contamination from past tenants. If you need any water testing, soil testing or air quality testing in the San Francisco Bay Area, please

Call 415-785-7986 or Fill Out This Form for a Free Quote


Healthy Building Science is an environmental consulting firm which provides mold testing and mold inspection services for commercial, residential, multi-family, buildings, offices, industrial and manufacturing workplaces, hospitals and medical facilities, and single-family homes in the greater San Francisco Bay Area and all of Northern California including the cities of San Francisco, San Jose, Oakland, and Sacramento.

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