It’s good that the city of Lawrence has established specific benchmarks for what constitutes affordable housing, but the city must remain open to changes to the policy as the market changes.

The new system defines not only what an affordable unit is but also how many affordable units a developer must include in a residential project to qualify for economic development incentives from the city. That certainly should make clear for developers what they’re getting into when they seek incentives from the city.

The new policy requires residential developments seeking incentives to set aside 10 percent of the units as affordable if there are fewer than 50 units; 15 percent if there are 50 or more units. The rents established by the city are the fair market rents calculated annually by the U.S. Department of Housing and Urban Development for the Lawrence market. For example, the fair value rent for a one-bedroom apartment in Lawrence for 2016 is $639 per month, including the cost of essential utilities like water, electricity and gas. For a two-bedroom unit, it’s $835 per month.

For projects that include homes or condos for sale, affordability will be based on income brackets. Payments can’t exceed 30 percent of household income for families that make 80 percent of the area median income.

“I think it gives us a quantifying measure, where we can actually look at something, and instead of just subjectively saying, ‘Oh, I think that is or isn’t affordable,’ we can actually tie it to a fixed market rate we have established,” said City Commissioner Matthew Herbert.

The new incentives policy is designed to address what has been defined as a severe shortage of affordable housing in Lawrence. U.S. Census data show 57 percent of renters and 28 percent of homeowners in Lawrence spend more than 30 percent of their monthly incomes on housing, qualifying them as “cost burdened.”

But it’s also important to note that the city is in the midst of the most rapid rate of apartment construction in its history. This year, a record number of building permits were issued for apartment construction — more than $40 million in projects adding 1,191 units. In all, an estimated 2,500 new apartment units are in some phase of construction.

That construction is likely to have a significant impact on the Lawrence market and the number of residents who are cost burdened. In turn, those market changes are likely to impact demand for affordable housing in future projects, especially those with only a handful of units.

It’s laudable for the city to try to increase the availability of affordable housing by clearly defining affordability and including it in its economic development incentives policy. But in the long run, changes in market demand may dictate changes in the policy.