A diminished development pipeline and higher renter demand is sparking an increase in suburban apartment rents and fueling investor interest.

Construction cranes around Greater Boston aren’t translating to a higher delivery of new residential product, and that is boosting rents, especially in the suburbs. The development pipeline in Cambridge is a mere 20% of what it was a year ago, according to a new Marcus & Millichap multifamily report. Vacancy rates across suburban Boston are hovering in the 3% range.

Monthly rents rose by just over 6% in 2018, and the report anticipates another 4.2% in growth this year.

Unit delivery is also expected to cool off this year. Marcus & Millichap forecasts 6,400 units to deliver, which will be the first time in three years deliveries have dropped below 8,000 units.

The overall state of the rental market is attracting investors, especially as lower yields in the urban core push teams to look at suburban markets like Salem, Lynn and Westborough.

The Marcus & Millichap report says investors are also pursuing higher short-term returns and value-add opportunities on the North Shore. Recent transactions almost exclusively involved century-old facilities with fewer than 20 units. Those properties saw first-year yields in the mid-6% to 7% range.

An affiliate of Northland Investment Corp. sold the 562-unit Fountainhead Apartments in Westborough to an affiliate of FPA Multifamily for $130M, CBRE announced Wednesday. The market-rate complex was originally built between 1971 and 1973.

The more than $231K/unit sale puts the Westborough deal between the average $142K/unit sale price Marcus & Millichap sees on Route 1 and the $411K/unit average sale price for developments built within the last 30 years closer to Boston.