Residential building approvals posted a surprise fall in April, but are still up on last year.

Bureau of Statistics figures showed a 5.6 per cent fall in total dwelling approvals last month to 14,931, seasonally adjusted.

Economist forecasts had centred on a rise of 1.8 per cent, according to a poll of 20 by Reuters.

However, overall building approvals remained 1.1 per cent higher than the same month a year earlier.

Further clouding the economic portent of the sharp monthly decline was the fact that most of it came in the notoriously volatile non-house sector, mostly made up of apartment developments.

Approvals of such multi-unit dwellings were off 14 per cent, while approvals for private sector houses were down just 0.3 per cent.

With a few large developments able to skew the apartment figures from month to month, many economists prefer to focus on the detached housing segment.

Although, with units making up an increasing proportion of the housing stock, a negative trend of -4.6 per cent in monthly non-house approvals should be of some concern.

The trend growth in approvals for detached houses was also weak, at just 0.5 per cent in April.