With vacancies still on the rise in commercial properties in most parts of the U.S., construction of new buildings is expected to be rare this year and next, the American Institute of Architects said Wednesday. Even with modest improvements in the economy, construction spending on hotels, office buildings, warehouses and malls is expected to decrease by more than 20% in 2010, followed by a marginal increase of about 3% in 2011, the architecture trade group said.