SYDNEY - [AAP] Shares in CSR Limited (ASX: CSR) have fallen at the open after the building products supplier raised first-half profit by 3.7 per cent to $118.7 million.

At 1055 AEDT, CSR shares were down 29.5 cents, or 6.22 per cent lower, at $4.445, despite a solid housing market helping lift first half revenue for the company behind Gyprock plasterboard and Bradford insulation.

Managing director Rob Sindel said earnings in CSR's core building products business rose 5 per cent thanks to the "relatively stable" conditions in Australia's detached housing market.

"The detached housing market in Australia, which accounts for almost 50 per cent of CSR's Building Products' revenue, remains stable, underpinned by record low interest rates and steady population growth," Mr Sindel said.

However, Mr Sindel said the high-rise apartment market has now slowed, although the company maintains a steady multi-residential pipeline that can support ongoing business activity.

CSR's aluminium business lifted earnings 27 per cent as the price of the metal hit a five-year high.

However, the company said a new power supply contract, effective from this month, will increase the power costs of aluminium production by $250 per tonne.

The company announced on Wednesday an interim dividend of 13.5 cents per share, franked at 50 per cent (6.75 cents), up 4 per cent on the previous half year unfranked dividend.

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