There's also steady demand for corporate rentals at the upper end of the market, but the higher the value of a property the lower the rental yield. Ken Woollcott, branch manager at Pam Golding Properties in Hyde Park, says yields on upper-end homes generally vary between 5% and 8%. He notes there's high demand for corporate rentals around the R20 000 to R30 000/month level in secure, cluster estates that offer state-of-the-art security.

"But if you're renting out a stand-alone house in an unsecured suburb, you'll battle to find a tenant."

FNB property strategist John Loos says a significant decline in new housing developments on the back of higher interest rates, rising building and land costs and electricity supply issues should underpin rentals over the next six to 12 months. "And steadily rising rentals will support further yield widening for buy-to-let investors."

Rode & Associates figures show that flat rentals in Johannesburg not only outperformed other cities over the short term but also over a two-year period, recording average growth of 14,5%/year since 2006. Durban followed with growth of 12,1%/year, with Pretoria, Cape Town and Port Elizabeth lagging at 5,5%, 5% and 4,5% respectively over the same period.

The steep rise in residential rentals in most Johannesburg suburbs means it's become more expensive to rent property in Johannesburg than in Cape Town. For example, Rode's figures show a standard two-bedroom flat in Johannesburg now rents for R4 014/month, while one of the same size and quality costs around R1 000/month less to rent in Cape Town at an average R3 030/month.