Perth's residential rental vacancy rate has reached a record high of 5.2 per cent with 10,738 homes without a tenant, according to property group SQM Research.

The July vacancy rate was more than double the national level of 2.5 per cent and had climbed a significant 1.4 percentage points in the past year.

The asking rent for houses in Perth has dropped 8.4 per cent in the past year and 10.8 per cent for units, SQM said.

Weekly rents for houses and units in Perth up to last week were an average $445.80 and $349.60 respectively, making the city cheaper than Sydney, Melbourne and Canberra.

Managing director Louis Christopher said overall vacancy rates remained steady for major capital cities.

“Perth continues to be the ongoing exception with further increases in vacancies this month as the mining downturn continues to hit the economy hard,” he said.

“Looking forward, I believe the national vacancy rate will continue to creep upwards.”

The results come after Perth office vacancies also reached their highest level in 20 years, according to the Property Council of Australia.