When only a portion of a building is subject to 521 CMR, the full and fair cash value shall be prorated by the ratio of the square footage of that portion to the square footage of the whole building.
Example: Where the whole building is 100,000 square feet, the full and fair cash value is $1,000,000, and the part subject to 521 CMR is 10,000 square feet (one-tenth of the total), then the full and fair cash value of the part subject to 521 CMR would be one-tenth of $1,000,000 or $100,000.
521 CMR, § 3.7