In theory, credits could increase in value if builders intensively sought them.

Mr. Dranoff and other builders are now seeking a similar abatement for new construction of residential towers.

Another cause was a surge in lumber prices between October and March that disrupted many transactions as builders sought to pass on their higher costs.

"Some builders seek variances based on a financial hardship created by a practical difficulty that makes it unprofitable for them to develop their land," he said.

With higher lumber costs adding $10,000 to the price of a 4,000-square-foot house, builders are seeking alternatives.

The rules, geared to maximum coverage, did not anticipate that builders would seek minimal lot coverage in order to construct the tallest buildings possible.

Many builders do not even seek the bonus, feeling that the uncertain and lengthy review process does not justify the benefit.

"We supported the town's one-acre zoning, so builders wouldn't seek a change of zone," she said.

The builders of Milan's cathedral sought his advice, but then quietly discarded it.

With the cozy cooperation of town planning boards, the builders seek quick, rubber-stamp approval of their projects.