Owners of apartments in the Opal Tower at Olympic Park in Sydney may have to wait at least two years before selling out and face losses of more than 16 per cent say valuers who have issued a lending alert on the building to their bank clients.

Leading valuation firm Preston Rowe Paterson said further issues were likely to stem from the Opal Towers incident including strata corporation legal actions, "likely drops in rent" and "increased insurance premiums".