OTTAWA — The little house on Thorson Road looks unremarkable: A modest 1960s bungalow, reddish-brown, plain and boxy. Nice lot. A park and a school nearby. And in June, the Ottawa police hauled 170 marijuana plants out of it.

The bungalow in the Pinecrest area now takes up one of four spots on a police website that lists grow-ops — indoor marijuana farms. But grow ops only stay listed for a few months.

A host of problems remain in houses that have been grow-ops, however, and the next owners of many such houses are looking at big trouble: Bad wiring, structural faults, toxic chemicals, and enough mould to choke an elephant. That’s the legacy of grow ops.

Royal Lepage agent Patricia Verge says Ottawa has 400 to 500 active grow ops at any given time. She says the figure comes from an Ottawa police drug officer who explained the full extent of the problem to real estate agents several years ago.

“Every area of the city is affected,� she said. “Every suburb. There’s nobody that’s exempt. They’re from Stittsville to Orléans. I’ve seen them in Greely.�

“Then people try to spiff them up a bit and put them back on the market for some poor unsuspecting family (to buy). It used to be a lot of bungalows. Now we see it in every kind of house.�

The damage runs deep.

Growers often steal electricity, and an Ottawa police summary of the problem says this may require drilling a hole in the foundation to hook up illegally. They cut through walls and joists to run extra ventilation and install booby traps. And they nourish the plants with heat and high humidity that can warp the wood everywhere — floors, stairs and framing lumber — and cause massive buildups of mould and even rot.

There’s often fungicide residue from plant spraying.

Fire hazards, such as exposed live wires and overheated electrical ballasts, are often found in the homes.

Now Nepean-Carleton Conservative MPP Lisa MacLeod has introduced a bill that would force the province to establish a registry of homes used for grow-ops and drug labs.

Currently, grow-ops discovered by police are listed on the Ottawa police website for three months, MacLeod said. After that, the information disappears.

“As a result, homeowners aren’t protected and people are moving into homes where there could be mould and poor air quality and significant damage to the house,� she said. If the building was also a meth lab, that adds a whole new level of toxins.

Verge is a director of the Ontario Real Estate Association, which supports the MacLeod bill.

“It’s a very difficult situation� today for agents to keep track of known grow ops individually, she said. “The bottom line is, if we could have a provincial registry it would be great.�

The province passed legislation in 2006 that calls on real estate agents to disclose whether a property was used as a marijuana grow house, assuming there are issues of safety and structural damage. If an agent knowingly fails to disclose that information, he or she faces an administrative fine and possible revocation of their license.

The law is administered by the Real Estate Council of Ontario.