Building products maker Boral has delivered a 65 per cent rise in first half net profit due to gains from acquisitions, but says weak housing markets continue to affect its underlying performance.

Boral posted a net profit of $153 million for the six months to December 31, 2011, up from $92 million in the previous corresponding period.

The result included an $86 million gain on the fair value of its acquisition of an Asian Asian plasterboard business.

Net profit excluding value gains and other significant items in the six months to December 31 was $67 million, down 28 per cent from $92 million in the previous corresponding period.

The underlying result reflected the extent of market declines in Boral's traditional Australian activities and a continuation of the difficult market for residential housing in the United States, chief executive Mark Selway said.

In January and February, the company's performance was negatively impacted by weather in Queensland and NSW, which weakened demand and delayed the start of new building activity, Boral said.

However, the company said it expected to deliver improved earnings in the second half of the 2011/12 financial year.