After years of gains, Portland's residential real estate market is finally showing signs of cooling down, except for one key factor.

While the total number of sales decreased and days on the market lengthened in the first quarter of 2017 compared to the same quarter last year, the average price of homes sold in the Portland area's 96 ZIP codes, continues to rocket upward. The prices jumped from about $369,000 last year to around $416,000 this year, or 12.3 percent, according to data provided by RMLS.

View slideshow: Average Sale Price

And this follows an 11.1 percent increase during 2016's first quarter. Inventory remains very tight despite some easing and demand is still quite brisk.

Among the top 25 ZIP codes with a minimum of 30 sales that had the highest average sale price, 15 topped $500,000, up from 11 in Q1 2016 and just five in Q1 2015.

Only one top 25 ZIP code saw a decline in average price — just -0.4 percent — and 10 experienced double-digit gains. Average price in the No. 2 'hood grew a whopping 49 percent.

Demand for local real estate is impressive, but if such increases continue through the rest of 2017, Portland's simmering affordability crisis may again boil over, and put the city's long-time reputation as the West Coast's most affordable metro in further jeopardy.

Read more: Where homes sold the fastest

The Portland Business Journal is a KGW News partner.