In the Chlorovinyls segment, fourth quarter 2012 net sales were $346.4 million compared to $321.5 million during the fourth quarter of 2011. The increase in net sales was driven by higher vinyl resin sales volumes and higher caustic sales prices, partially offset by lower vinyl resin sales prices and lower caustic sales volumes. The segment posted operating income of $77.0 million in the fourth quarter of 2012, compared to operating income of $21.5 million for the same quarter in the prior year. The $55.5 million increase in operating income was primarily due to lower feedstock costs, higher vinyl resin sales volumes and higher caustic sales prices.
In the Building Products segment, net sales were $190.8 million for the fourth quarter of 2012, compared to $189.7 million recorded for the same quarter in the prior year. Net sales for the fourth quarter of 2011 include $2.6 million of sales from the fence product line that was discontinued in March 2012. The net sales increase was driven by increased Canadian sales volume, partially offset by lower sales volume in the U.S. due to the discontinued fence product line. On a constant currency basis and excluding the sales from the discontinued fence product line, net sales for the quarter were flat compared to the fourth quarter of 2011. The segment's operating loss was $5.3 million for the fourth quarter of 2012, compared to an $11.6 million operating loss during the same quarter of the prior year. The fourth quarter 2012 operating loss includes $1.0 million of restructuring costs while the fourth quarter 2011 operating loss includes $2.4 million of restructuring costs and $8.3 million of asset impairment charges. After excluding these items, the increase in operating loss was due to higher selling, general, and administrative costs partially offset by improved gross margin.