Private owners who want to refurbish and enhance low-grade office towers face a tougher job than many people realise, says the owner of a Melbourne commercial building who’s just completed a $10 million upgrade.

Designer Lou Weis, who co-owns the 11-floor, 3400-square-metre building at 124 Exhibition Street in the CBD, said they only embarked on the major renovation of their 1971 building after not being able to sell it for a price they were prepared to accept.