X0303 4 2011-05-04 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 2011-05-04 4 S 0 100 29.064 D 118841 D Common Stock 2011-05-04 4 S 0 200 29.13 D 118641 D Common Stock 2011-05-04 4 S 0 100 29.152 D 118541 D Common Stock 2011-05-04 4 S 0 100 29.158 D 118441 D Common Stock 2011-05-04 4 S 0 262 29.16 D 118179 D Common Stock 2011-05-04 4 S 0 400 29.17 D 117779 D Common Stock 2011-05-04 4 S 0 38 29.18 D 117741 D Common Stock 2011-05-04 4 S 0 100 29.191 D 117641 D Common Stock 2011-05-04 4 S 0 100 29.20 D 117541 D Common Stock 2011-05-04 4 S 0 200 29.14 D 117341 D Common Stock 2011-05-04 4 S 0 100 29.142 D 117241 D Common Stock 2011-05-04 4 S 0 300 29.144 D 116941 D Common Stock 2011-05-04 4 S 0 200 29.145 D 116741 D Common Stock 2011-05-04 4 S 0 200 29.146 D 116541 D Common Stock 2011-05-04 4 S 0 300 29.15 D 116241 D 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 2011-05-05