Imagine if every Canadian adult was allowed to grow marijuana at home. What would this do to our real estate market?

The answer depends on who you ask.

In Colorado, where pot has been legal since 2014, homeowners can keep up to half a dozen pot plants indoors — and that's causing a "green boom" in cities like Denver.

"A lot of people are into the grow-your-own movement out here in Colorado and most of my people are growing cannabis for medical use," said Rona Hanson, a longtime realtor in Denver who runs a grow-friendly listing called Need Room to Grow

"I find houses that have areas in them or spaces that people can have small home gardens, whether it's for growing cannabis or just doing herbs or whatever they like," said Hanson, adding homes with proper greenhouses tend to sell more quickly.

"We have 120,000 people moving to our state each year for reasons that include the cannabis freedom that we have."

Mould, vermin, chemical contamination concerns

If you want to grow cannabis at home (for medical use only) north of the border, you have to apply for a licence through Health Canada.

The Access to Cannabis for Medical Purposes Regulations came into effect in August 2016. Because these personal licences involve sensitive medical information, it's difficult to find out who is growing at home and where.

As the Liberal government moves ahead to legalize marijuana in 2017, the scope of the law could very well expand.

And, if we go the way of Colorado, home buyers best start looking for a good house inspector.

"The marijuana plant requires a lot of humidity for it to prosper," said Gary Barnes, president of Western Site Technologies in Calgary.

"Even for six plants, that is ultimately going to cause problems unless you have proper air exchange."

mold marijuana grow-op

'The marijuana plant requires a lot of humidity for it to prosper,' says Calgary environmental consultant Gary Barnes. (Western Site Technologies)

Good airflow costs money, and Barnes doubts most homeowners would actually pony up the cash for a small weed operation.

"I don't think you're going to put in a multi-thousand-dollar air exchange system in your house in order to control that. Therefore you're going to get mould."

And mould is not good.

"Depending the extent of the damage, whole walls might have to be ripped out," said Adam Jackson, who works with government officials to oversee the remediation of grow-op homes in Alberta.

But mould is just the tip of the iceberg in terms of potential damages.

"There are a number of nuisances that take place," said Jackson.

"It can be anything from the chemicals and fertilizers being dumped down the drain, or they're leaching through the carpets and the walls. Bugs are another big thing. People will use pesticides."

Buyer beware, especially during transition period

In the past, when someone grew pot at home, that person was breaking the law. Police had every right to bust the criminal.

But now that some Canadians have been given private licences to grow at home, it has become a confusing, transitional period — and Barnes said law enforcers are more reluctant to crack down.

Marijuana grow-op

Along with mould damage, pesticides and fertilizers used to grow marijuana indoors can leach through carpets and walls. (Western Site Technologies)

In the past, Alberta Health Services appointed Western Site Technologies about 60 remediation cases per year. This year, the company has received two.

"I'm sure there are houses on the market right now that have been grows that are going to have no disclosure and it's buyer beware," Barnes said, adding that this is an issue that affects any type of house.

"You think you're going to into an upscale neighbourhood and buy a house that's a million dollars and you figure nobody's going to put a grow on that? You're wrong."


With files from the Calgary Eyeopener