Demand for greater Vancouver rental apartment buildings remains strong, despite rising prices and a steady supply of investor-owned condominiums for rent.In the past two weeks, two multi-suite buildings -- one in Coquitlam and one on Vancouver's West Side -- each sold within 24 hours of being listed."There are chronic shortages of rental housing product in all jurisdictions of Greater Vancouver, while demand [from landlords] remains insatiable," David Goodman, a commercial realtor with Macdonald Commercial Real Estate Services, said Thursday. "As soon as we list something, within 15 minutes the phones start ringing."As tenants move into new condo towers, either as first-time buyers or renters, he said a new breed of investors is buying up older rental buildings to give them major upgrades and charge higher rents for the next tenants."If you profile the renter today in Vancouver, many have well-paying jobs and security of employment, but they don't have the $100,000 down for the new condo," Goodman said in an interview. "They can pay these higher rents and they want to pay these higher rents because they are getting a better unit.