Now that cannabis is legal, are marijuana grow houses still something to be concerned about?

Even though marijuana and cannabis products are now legal for use in Ontario, grow houses and grow operations remain a valid concern for home buyers. Thank you for asking this question.

A marijuana grow operation (MGO) is a building or residence that has been converted to a plant nursery for the purpose of accommodating mass production of marijuana and cannabis. These properties house well beyond the four-plant maximum permitted in a residence by provincial law.

Properties acquired for grow operation purposes may undergo extensive modifications in order to convert them into viable and high-producing MGOs. The modifications typically include potentially dangerous changes like tampering with electrical wiring, installing irrigation devices and industrial exhaust fans, and bypassing utility meters. All of these modifications can be costly to remediate properly.

Residual damage caused by extensive indoor agriculture and the chemicals used in the growing process may lurk behind the walls, in attics and under floorboards. This can include mould and mildew, resulting from extensive exposure to high humidity levels, and chemical residue which can create or exacerbate respiratory problems and allergies. From a safety perspective, rewiring and overriding hydro lines and amenity conduits can present significant risks and may make the property uninsurable.

It can be hard to spot the signs that a home or property was formerly used as a MGO. Mould can be especially difficult to detect. Enlisting the services of experts is the best way to determine if a home is a former grow op.

A home inspector may be able to identify readily visible signs of past grow-op use. A professional engineer can identify possible structural damage, and an environmental consultant can identify the presence of toxic mould in the structure. Finally, a general contractor may be able to estimate the cost of necessary repairs to the structure and household systems to bring it back to building and safety standards.

Buyers can also request an environmental clearance certificate following an engineering or environmental inspection, providing confirmation that damage has been remediated and the property meets required standards.

When considering purchasing a home that has been identified as a former MGO, do your research and work with your salesperson to ensure you fully understand the possible risks, additional costs and legacy factors. Once a property has a negative factor which leads to stigma, that fact must be disclosed by the salesperson or broker every time it is listed for sale or lease.

Sellers would be wise to discuss with their real estate lawyer the disclosure of any knowledge about a property’s history relating to its use as an MGO, to prevent facing potential legal action.

If you have a question for Joe about the home buying or selling process, please email

Joseph Richer is Registrar of the Real Estate Council of Ontario (RECO). He is in charge of the administration and enforcement of all rules that govern real estate professionals in Ontario. You can find more tips at, follow on Twitter @RECOhelps or on YouTube at

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