X0303 4 2011-06-01 0001069878 TREX CO INC TREX 0001201351 KAPLAN RONALD W C/O TREX COMPANY, INC. 160 EXETER DRIVE WINCHESTER VA 22603-8605 1 1 President and CEO Common Stock 2011-06-01 4 M 0 16174 8.80 A 124719 D Common Stock 2011-06-01 4 F 0 4728 29.74 D 119991 D Common Stock 2011-06-01 4 D 0 4971 29.74 D 115020 D Common Stock 2011-06-01 4 S 0 619 30.51 D 114401 D Common Stock 2011-06-01 4 S 0 100 30.47 D 114301 D Common Stock 2011-06-01 4 S 0 200 30.46 D 114101 D Common Stock 2011-06-01 4 S 0 100 30.36 D 114001 D Common Stock 2011-06-01 4 S 0 200 30.35 D 113801 D Common Stock 2011-06-02 4 S 0 6475 29.30 D 107326 D Stock Appreciation Right 8.80 2011-06-01 4 M 0 16174 0 D 2009-01-07 2018-01-07 Common Stock 16174 57355 D 16,174 Stock Appreciation Rights (SARs) are being exercised pursuant to Rule 10b5-1 trading plan adopted by the reporting person on November 3, 2010. 4,728 shares are being surrendered as allowed by the Company's 2005 Stock Incentive Plan to cover the payment of taxes currently due on the exercise of SARs. The stock appreciation right becomes exerciseable in three equal installments beginning on the first anniversary date of the transaction date. The sales reported in this Form 4 were effected pursuant to Rule 10b5-1 trading plan adopted by the reporting person on November 3, 2010. /s/ William R. Gupp by power of attorney 2011-06-02