The largest hospital in Massachusetts wants to grow even larger.

Massachusetts General Hospital officials unveiled a plan Tuesday to grow the hospital by 1M SF spread across two 12-story towers. The expansion would include cancer and heart centers, 450 single-patient rooms and inpatient and outpatient centers. The project is expected to have a final price tag of more than $1B, with donors picking up 20% to 30% of the tab, WBUR reports.

Although MGH is regarded as one of the top hospitals in the U.S., only 38% of its beds are in single rooms. MGH officials wrote in a letter to staff that this is “well behind” peer hospitals. The hospital has just over 1,000 beds and typically operates close to capacity.

“Single-bed rooms — the national standard of care for new hospital construction — offer privacy, space for families and a quiet and calm environment to foster recovery and healing," MGH President Dr. Peter Slavin and MGH CEO Dr. Timothy Ferris said in the letter obtained by WBUR.

The expansion would take place within MGH’s existing campus, and the buildings would front Cambridge and Blossom streets. Pending approval from Massachusetts and Boston agencies, the hospital hopes to break ground in 2020 and open in 2026.

Hospital expansions haven’t come easily in recent years. The Massachusetts Health Policy Commission warned in 2016 a $1B expansion proposal from Boston Children’s Hospital would lead to higher medical costs by pulling patients from competing providers. The Department of Health still approved the project with the condition Boston Children’s would keep price increases under control. Massachusetts targets keeping healthcare cost increases below 3.6%.

Mass. General's expansion received early support from Boston City Hall.

“It’s important that our hospitals are making the improvements needed to keep Boston at the global forefront of health care,” Boston Mayor Martin Walsh said in a statement to the Boston Globe. “We look forward to closely reviewing Mass. General Hospital’s proposal once it is filed and beginning the comprehensive public process with input from the community.”