A London family fears financial ruin at the hands of city hall, after a measurement error put them afoul of heritage regulations.

Alistair Dorward has a court date on Monday, but fears the small mismeasurement could force them from their Duchess Avenue home.

“They have told me they are after a substantial fine, and I have no idea where that is going to come from, what we are going to do,” he says.

The young father, with another baby on the way, faces a fine up to $50,000 and up to a year in jail.

It’s all because the city claims the new dormer constructed on his roof is larger than his heritage permit allowed.

Living in the Wortley Village Heritage Conservation District, he followed the rules, first getting a heritage alteration permit and then a building permit before construction began.

But once the walls of his attic were opened up, it was realized the dormer "as designed" wouldn't provide enough head clearance on the stairs to meet the building code.

Dorward says the dormer was, “widened by a foot and a half on either side and it was raised by eight inches, that's it.”

To keep the dormer symmetrical and roof slope the same the contractor extended the dormer 18 inches on each side and subsequently raised the peak to the roofline.

Then in the summer city hall posted a notice on their door.

Unable to resolve the issue because building it to the heritage permit plan would violate the building code, Dorward has now been charged with violating the heritage act.

“It’s tens of thousands of dollars I certainly don't have,” Dorward says, “and they've ordered me to immediately commence reconstruction, however with this weather I think it would be suicidal to open the roof of my house. Where would my two-year-old, my wife and I sleep?”

Neighbours who support the family, but who also argued in favour of a heritage district, say this could have a chilling effect on potential future heritage districts.

During public input on the issue in 2013, some Wortley homeowners worried becoming a heritage district would make modifying their homes difficult – and put too much control in the hands of city staff.

City hall declined an interview request, stating in an email that "because this matter is before the courts, we aren't able to provide any comment on the specifics of this situation."

A list of 14 neighbourhoods is being considered by city hall for future heritage districts, including North Talbot, Soho, Lambeth, Hamilton Road and Orchard Park.

Dorward says he’ll likely sell the house at a loss and move, but the whole issue has caused rifts in his family.

“I want to resolve this myself but I also want to make the city and residents of the residents city and other heritage districts aware of what's going on and what issues they could face.”