Yes, the gross leasable area includes vacant spaces. A vacant
space is a leasable area, it just happens to not be leased. When
calculating a tenant's share of costs it's always more favorable to
have your share based on leasable square footage. That way, you are
not being penalized for vacant spaces. If your lease states that
your share is based on leased square footage, then all vacant
spaces are taken out of the equation and the share of costs is
being spread across a smaller pool of tenants. This is not
beneficial to the tenant, but is beneficial to the landlord.