Companies trying to save on real estate costs are pondering their spatial needs and cutting back on a large scale. The shift will likely push South Florida’s office vacancy rate to a five-year high. Businesses connected to the housing sector are most aggressive in their desire to leave leases or sublease their own space, according to Grubb & Ellis. A year ago, a little more than 1 percent of the 59 million square feet of Broward and Palm Beach county office space was available for sublease, the firm said. That’s now close to 2.5 percent and expected to keep climbing. Troubled bank Washington Mutual, IBM and DeVry Institute are among companies looking to sublease space.