Homeowners with illegal accessory apartments - such as a basement rented out to someone other than the homeowner - have until Friday to avoid coming up with a $4,669 lump sum to pay the required impact fee.

By telling city officials that they have such an apartment on their property, homeowners will be allowed to finance the fee at $100 per month over a period of 56 months - finance charges included. Also required is an application fee of $100 and inspection of the apartment. If such property owners fail to tell officials about their rental units by the Friday deadline, the city will charge them the lump sum, due on demand.Failure to comply with the city's accessory apartment ordinance is a Class C misdemeanor and carries a $1,000 fine, 90 days in jail or both.

All that is according to a letter sent to residents by Mayor Richard Young. The move is part of a process city officials have instituted to count all the dwellings in town.

It's all part of a new effort to enforce a year-old city ordinance requiring that accessory apartments meet certain standards. Most such apartments here are considered illegal, a city official said. The official requested anonymity because "the mayor has told us not to issue press releases." Young was not available for comment.

Once the dwelling unit count is done, the city may then issue dwelling unit certificates that someday could become a hot local investment instrument. Developers will need them to obtain building permits, much like they need water share certificates now once the City Council passes an ordinance authorizing the new certificates. Just how valuable they could become is anyone's guess, the official said.

The certificates would allow density to be shifted from one property to another, but density would still be limited by zoning. Still unclear is whether the certificates will go to people who own houses in Mapleton or just to the owners of vacant, developable land, said City Councilman Stuart Newton.

The impact fee property owners need to pay now to have a legal accessory apartment is $4,669. The city collects the same amount for any new dwelling.

The decision to collect the impact fee didn't come as council action but was the mayor's decision, Newton said. "The first I heard of it was when I got the letter," he said.

While nearly all accessory apartments in the city are considered illegal, city officials don't know where they all are. Less than a dozen they do know about will be grandfathered in if they were built before Jan. 5, 1970 and used continuously as an apartment, or if the owners have been paying multiple sewer fees, the official said.