The fencing off of some 40 percent of a beloved rooftop garden in Kendall Square comes in mid-to late August, a developer revealed Wednesday.

The fencing off of some 40 percent of a beloved rooftop garden in Kendall Square comes in mid-to late August, a developer revealed Wednesday, surprising members of the Cambridge Redevelopment Authority who continued to suggest significant design changes to the structure going up inside those fences.

A further revelation: Some of the designs submitted by developer Boston Properties to the authority’s board of directors, including the very basis for the size of the structure, continue to be guesses. Its tenant, Google, hasn’t submitted formal plans for what it plans to put inside its planned, two-story connector building between 4 and 5 Cambridge Center, said Kevin Sheehan, a project manager for Boston Properties.

In addition to putting up construction fencing and taking other preparatory steps, the company will order steel to be used in framing the structure that will link Google offices in Boston Properties-owned buildings around the parking garage that forms the base of the garden, Sheehan said. (A four-story connector building is proposed for between 3 and 5 Cambridge Center for the same purpose.)

“It seems to me that if you’re already fencing off portions of the garden you’re taking, it renders somewhat moot responses to the design comments we’ve had. It treats it as an exercise of form over substance,” said Chris Bator, one of the five-member board.

Not so “conditional”

Although the board has design approval over the Google connector building, its members were appointed or activated only after the City Council approved Boston Properties’ plan. It too has approved the plan, although the 4-1 vote doing so June 20 was for “conditional approval,” with the conditions being the answering of a dozen design concerns. Sheehan explained last month what that meant from the point of view of Boston Properties: Nothing major could be changed from that point on. And Michael Cantalupa, senior vice president of development at Boston Properties, outright rejected the concerns and suggestions of board member Barry Zevin that were part of that conditional approval.

Despite that, board members seemed taken by surprise again Wednesday.

When an audience member expressed alarm that construction seemed to be starting even while major design questions were being debated, board chairwoman Kathleen Born said, “That’s up to them,” and expressed her understanding that the company still needed building permits and “I think there are some other things that need to happen,” suggesting the fencing and other steps should be seen as tentative, not final.

Sort of. Sheehan’s response:

We typically do start construction on initial levels of design review approval. Design documents evolve, and the final approvals are really typically more focused on finish materials that can be specified later in the process. [Such approvals are] set up to facilitate construction projects that are tied to a schedule, such as this one. It contemplates that things may happen in parallel … the basic structure of the new construction is outlined in the schematic submission and, as I think we indicated at the last meeting — and I don’t want to give the impression that we’re not listening, but I hope you are listening to us as well — we feel very strongly about the footprint of the areas we have proposed. We have good reasons and are happy to spend more time describing them to you.

“The fact is, based on the City Council’s approval … this is the area we’ll be working with,” Sheehan said, although he also tried to assure the board by telling them the fencing goes “does not necessarily dictate how big the connector is.”

Born was also mildly surprised Sheehan didn’t have a comprehensive answer to the dozen design concerns. “What I expected,” she said, was that he would “come back with a point-by-point response to each of the schematic design considerations that had been raised … I think all this was supposed to be was an opportunity for you to submit your latest design.”

Sheehan confirmed that the company hadn’t responded to the design questions, but “we expect to do so in the next submission,” when the board holds its September meeting. The dialogue Wednesday helped, he said.

One of the board’s major concerns was that whatever Google wanted inside its rooftop connector worked with the transparent (and, as Born described it, “glimmery” and “shimmering”) structure Boston Properties proposed to build. Having desks, filing cabinets and trash cans jammed up against glass walls wouldn’t be right, Bator said, and Google workers constantly pulling curtains or screens around their meetings would be just as bad. Born didn’t want to see walls just inside the glass structure, and both encouraged the company to put passageways toward the outside instead.

Not so certain

Sheehan and a representative of architect Elkus Manfredi seemed to like the ideas, but their comments confirmed that Boston Properties was set to build a shell without knowing fully what went inside. “The design of the building has been very consistent as it evolves,” said Steven Dube, a senior associate at the firm. “But we don’t really know what the interior configuration will be.”

“Maybe in the course of planning, they decide they need more desks, and it becomes used as functional workspace,” Sheehan said. “Again, we don’t have formal plans.”

The combination of Boston Properties’ refusal to yield on the size or design of the building but affirmation Google could yet change plans for its use disturbed at least two members of the board. “If in the end Google wanted it to be all office space, is there really any reason to keep quite as much room?” Margaret Drury wondered.

For Zevin, it seemed yet another blow to his confidence in even conditional approval of the plans, which were based on drawings that were only now being explained to the board as subject to change.

At the East Cambridge Planning Team meeting, they made a great deal of the need for what you call contiguous space, for open, flowing, prairies of space,” Zevin said, recalling the extensive testimony of Google’s Steve Vinter on how broad stretches of open floorspace was needed for the company’s brand of innovation. “And once again the actual proposal we saw absolutely belie that … I’m really puzzled by your claiming again their need for this contiguous and therefore wide open, wide space.”

The focus on what kind of glass should be used to clad the building if it becomes mere office space, compared with the impact on the public losing the open space “was talking about painting deck chairs on the Titanic.”