Two of Salt Lake County’s five school districts are holding bond elections this year, and a third one passed a bond last year. What gives?

It’s the combination of low interest rates, rising construction costs and a healthy Utah economy.

Granite School District, the third largest in the state, is proposing a 10-year, $238 million bond to rebuild or remodel 31 schools. Granite is a district that spans the Oquirrhs to the Wasatch, and it’s politically convenient that the two high schools recommended for replacement — Skyline and Cyprus — are at opposite ends.

The Granite bond money also would rebuild 12 elementary and junior high schools and remodel 13 more. Hunter and Taylorsville high schools also would get remodels. Granite has received some pushback to remodel rather than replace Skyline, a unique mid-century school building. Either way will take millions, so that decision isn’t about the need for the bond, which would add $184 annually to the property taxes on a $250,000 home.

Canyons School District, in the southeast corner of the valley, proposes a $283 million bond to rebuild Hillcrest and Brighton high schools, Union Middle School and three elementaries and remodel several others. Most of the schools are old but not ancient. Brighton, age 48, apparently is no longer fit for service. Because Canyons is retiring old debt, no tax rate increase is needed, but voters are passing up a possible tax reduction if they approve the bond.

Some Canyons schools would get something profoundly simple: sunlight. Schools built in an earlier era tended to have fewer windows and more artificial light, so the district will go in and add windows and skylights to 18 elementaries. Window gazers, rejoice.

Canyons also is earmarking bond money for a “West Draper Elementary” somewhere in the soon-to-be-developed Utah State Prison site. The specifics of that development are unknown, but it’s reasonable to expect housing and schoolchildren as part of it.

A year ago, it was Jordan School District, in the southwest corner of the valley, that managed to pass a $245 million bond. In Jordan, it’s all about growth, and about a high bedroom-to-business ratio that makes it hard to fund that growth.

Granite and Canyons are in more mature areas where the school population and tax base has been more steady, so the districts have to make the case that current buildings no longer work. Armed with analyses and consultants’ reports, they can argue their cases on the basis of energy efficiency, seismic safety, security and the latest thinking on effective learning environments.

Utahns remain dedicated to their public school systems, and the time is ripe for investment. These bonds deserve to pass.