Warren Buffett's Berkshire Hathaway (NYSE:BRK-A) (NYSE:BRK-B) is strengthening its presence in the building products sector. The company has boosted its stake in USG (NYSE:USG) following the conversion of a set of senior convertible notes, it revealed in an SEC filing published today. Following the conversion, Berkshire Hathaway holds slightly less than 43.4 million shares of the company, giving it 30.5% of the outstanding amount. 

In a previous filing made before the conversion, Berkshire said it held 17.1 million shares of USG. It has had a position in the company since 2000. 

Berkshire Hathaway is the largest shareholder in USG, which manufactures sheet rock and related products used in housing construction. In its most recently reported quarter, USG posted net sales of $925 million and a net income of $23 million ($0.21 per diluted share). Both figures were improvements over the $828 million and net loss of $29 million ($0.28) in the same quarter the previous year.