The ballooning costs of construction materials and labor over the past two years have hit the Tisbury School project hard. What had been an estimated $53 million renovation and addition little over a year ago is now pegged — through actual bids from contractors — at nearly $82 million, a 54 per cent rise.

“Influences in the world affect what we do, even on Martha’s Vineyard,” said Michael Owen of Daedalus/CHA, owner’s project manager for the Tisbury School building committee, at an online meeting with the select board Wednesday.

The board agreed to call a special town meeting Sept. 20, to ask voters for a Proposition 2 1/2 override authorizing another $26 million in borrowing on top of the $55 million approved at last year’s annual town meeting.

Select board members discussed setting Oct. 4 for a town election on the debt exclusion, but agreed to wait until their next meeting when town clerk Hillary Conklin can be present.

Inflation, supply chain problems, workforce shortages and complications in logistics all have contributed to blow up the original budget, architect Chris Blessen said, even after his firm Tappé Architects reworked the plan earlier this year to shave $10 million by reducing the administrative addition, choosing some less expensive finishing materials and dropping landscaping, masonry and windows from the project until supplemental funding can be found.

The new, $81,843,284 budget unveiled this week restores the windows and masonry work, but does not include fencing, playground equipment or photovoltaic equipment for the solar-ready roof.

Construction costs and materials represent the lion’s share of the new budget, at $71,221,289.

"We do know factually that steel was the highest increase," Tisbury planning board chair Ben Robinson said.

Architecture and design are next at $4,521,920, followed by a $2.73 million contingency line. Mr. Owen’s company is budgeted for $1,680,230 and $825,000 is earmarked for furnishings and equipment such as telephones, computers and other technology.

The complete budget is posted at as part of a 20-page report released this week by Daedalus/CHA, which also includes detailed explanations of the circumstances behind the sharp cost increases.

If approved by voters this fall, the additional $26 million in borrowing would, combined with the initial $55 million, push property taxes up by roughly 15 1/2 per cent for the 30-year life of the bonds, Tisbury finance director Jon Snyder said.

That would equal more than $1,000 a year on the town’s median property value of $744,000, Mr. Snyder said.

But the hike would be appreciably steeper if not for Tisbury’s AA+ bond rating, recently reaffirmed by Standard and Poor’s for the eighth or ninth year in a row, town administrator Jay Grande said.

The credit-rating giant also applied Tisbury’s AA+ rating to the school bonds voters authorized last year, Mr. Grande said.

“Honestly, that is great news,” Mr. Grande said. “That means our bond will be well received among the buyers next week, and it means we will get very competitive interest rates.”

Should voters turn the borrowing request down, there’s no clear alternative for Tisbury School, which graduated its first class in 1930 and has been plagued with lead, asbestos and building envelope problems in recent years.

“We have a very sick building. Regardless of what we do, it needs abatement, and it doesn’t meet our overall needs from a programming perspective,” school building committee chair Michael Watts said at Wednesday’s meeting, adding that significant amounts have already been spent on the project.

“If we don’t get the money, we have 10 to 15 million just sunk, gone, and we haven’t solved the problem of our sick building,” Mr. Watts said.

Select board chair Roy Cutrer and recently elected member John Cahill both winced at the enormity of the new total, while board member Larry Gomez was not present at Wednesday’s meeting.

“It’s such a significant number,” Mr. Cahill said. “That’s not chump change for a lot of people in this town, and they’re going to have to carry it for a long time.”

But Mr. Cutrer said moving forward with the borrowing request is in the town’s best interest.

“If I look at the alternative of not having the new Tisbury School and what that means to the community, [and] when I look at what we’ve already spent trying to reach that goal of having a new school for the town of Tisbury … not moving forward is wasting money and wasting millions,” Mr. Cutrer said.

The Tisbury select board meets next on Wednesday, August 3. Board meetings usually are scheduled to begin at 4 p.m. and agendas are posted on the town website at least 48 hours earlier.