CSR expects to make a decision on whether it will spin off Viridian glass by the end of the year, after the troubled business weighed heavily on the construction material supplier's half-year result.

CSR announced on Friday its half-year profit plummeted 77 per cent to $26.8 million on the back of nearly $76 million in impairments to Viridian, sending shares in CSR more than eight per cent down in early trade.

They were worth $3.30 at 1055 AEDT, down from $3.59.

CSR had earlier flagged Viridian as a potential sale item ahead of commencing a review in July.

"While Viridian's earnings have improved in the first half of the financial year, the performance remains below internal targets," the company said in a note.

"(The July 2018) review is materially progressed and the company expects to make a final decision by the end of this calendar year."

CSR said its revenue lifted 6.0 per cent to $1.4 billion, though steady demand from the detached housing market and growth in commercial projects was offset by slower activity in high-rise apartments, and a drop in earnings on aluminium.

Excluding Viridian, the company's half-year net profit after tax was down 31 per cent to $94 million.

CSR is issuing a dividend of 13 cents, fully franked, down from 13.5 cents, 50 per cent franked, during the last interim period.

CSR's H1 RESULTS:

* Net profit down 77pct to $26.8m

* Revenue up 6.0pct to $1.4b

* Interim dividend down 0.5 cents to 13 cents, fully franked