City and school officials drilled down on details of the proposed renovations at four elementary schools in Portland on Tuesday night as they weigh whether to put a $70 million bond out to voters for the fixes.

Architect Tyler Barter of Oak Point Associates walked the School Facilities Ad Hoc Committee through the latest plans for Presumpscot, Longfellow, Lyseth and Reiche elementary schools, which the committee toured in recent weeks.

Barter pointed out that at the schools – all 40 to 60 years old – replacing aging plumbing and electric systems is a significant cost in addition to new construction.

“It’s most important to explain the learning needs,” Superintendent Xavier Botana said, joining Barter at the podium to address the committee. He said if the renovations are approved, the extra space would be used for new learning spaces, pre-K rooms, hands-on learning labs, expanded libraries and media labs, and music and art rooms.

At all the schools, the renovations would create new, separate gymnasiums and cafeterias, a high priority for school officials who can’t use the space when students are eating. In bad weather, that means some students get their exercise in classrooms, Botana said. Each school would also get a pre-K classroom for 18 students.

The additional space at three of the four schools wouldn’t increase the enrollment capacity, but it would ease cramped conditions, Barter said. Currently, all the schools are using odd spaces, from closets to hallways, as office space for social workers or learning space for students.

Several committee members pressed for details on ways to reduce costs. A second floor at Presumpscot, which has declining enrollment, may not be necessary, Botana said.

More than $5 million in costs, described in Oak Point documents as “renovation non-equity” costs, are not new construction costs, but are for deferred maintenance that school officials had requested be covered by city capital improvement funds in the past.

Barter’s full presentation is viewable here. Among the details of the proposed renovations at each school:

• Presumpscot: $16.1 million. Adds 36,000 square feet, more than doubling the existing 29,000 square feet. Eliminates portable classrooms. Adds a two-story “classroom wing” off the back of the school, over the space used for the portable classrooms. Adds a new entryway that includes additional space for administrators, social workers and other student specialists who need privacy. New space allows for separate music and art rooms. Reconfigures drop-off area to encourage parents to use the Sherwood Street entrance, and adds parking along the back of the school. Deferred maintenance costs are $424,113. Eliminating second floor would save about $2.5 million.

• Longfellow: $16.3 million. Adds 17,000 square feet to existing 43,000 square feet. Adds elevator and reconfigures main entrance with ramps to make it accessible. Expands into the current parking lot, and partly into a teaching garden and playground. Opens an “area well” alongside building to allow natural light into basement rooms. Adds boiler to update heating system. Creates new discovery lab, new finishing kitchen area and larger music room and expanded library. Moves some teacher parking to existing Deering parking area. Deferred maintenance costs, including new masonry and replacing windows, are $1.6 million.

• Reiche: $17.9 million. Adds 6,000 square feet to existing 73,000 square feet. Addresses common complaint of acoustics through additional insulation, adds lighting, skylights and windows to increase natural light. Reconstructs main entrance, reconfigures space so all younger students are together on ground floor. Deferred maintenance costs, including new roof and replacing windows, are $2.7 million. High project costs are largely due to about $5 million in utility projects, including upgrades to heating system with piping under concrete slab.

• Lyseth: $20.2 million. Adds 37,000 square feet to existing 51,000 square feet. Adds a two-story wing across one of the open courtyard areas. Reconfigures entryway and moves expanded library across from entryway. Adds new gym with stage. Reconfigures current parent drop-off and bus area to widen roadway, eliminates some existing parking and move parking to near ball field, with a net addition of about 30 parking spaces. Deferred maintenance costs are $683,502. City is currently working on drainage issues and stormwater updates, so those costs are not part of the upgrades.

The next meeting of the committee is scheduled Sept. 12 at 5 p.m.