X0306 4 2018-02-22 0001069878 TREX CO INC TREX 0001430183 Cline James E C/O TREX COMPANY, INC. 160 EXETER DRIVE WINCHESTER VA 22603-8605 1 1 President and CEO Common Stock 2018-02-22 4 M 0 9286 12.78 A 68736 D Common Stock 2018-02-22 4 D 0 1117 106.27 D 67619 D Common Stock 2018-02-22 4 S 0 300 102.9167 D 67319 D Common Stock 2018-02-22 4 S 0 1500 104.3233 D 65819 D Common Stock 2018-02-22 4 S 0 1800 105.2956 D 64019 D Common Stock 2018-02-22 4 S 0 5300 106.5217 D 58719 D Common Stock 2018-02-22 4 S 0 3187 107.5529 D 55532 D Common Stock 2018-02-22 4 S 0 413 108.3812 D 55119 D Common Stock 2018-02-22 4 S 0 500 111.852 D 54619 D Common Stock 2018-02-22 4 S 0 500 115.42 D 54119 D Common Stock 2018-02-23 4 S 0 7300 105.9987 D 46819 D Common Stock 2018-02-23 4 S 0 869 106.99 D 45950 D Stock Appreciation Right 12.78 2018-02-22 4 M 0 9286 0 D 2013-02-15 2022-02-15 Common Stock 9286 9286 D Stock Appreciation Rights are being exercised pursuant to a Rule 10b5-1 sales plan adopted by the reporting person on August 24, 2017. The sales reported in this Form 4 were effected pursuant to a Rule 10b5-1 sales plan adopted by the reporting person on August 24, 2017. The price reported in Column 4 is a weighted average price. These shares were sold in multiple transactions at prices ranging from $102.56 to $103.24, inclusive. The reporting person undertakes to provide Trex Company, Inc., any security holder of Trex Company, Inc., or the staff of the Securities and Exchange Commission, upon request, full information regarding the number of shares sold at each separate price within the ranges set forth in Footnote (3) to this Form 4. The price reported in Column 4 is a weighted average price. These shares were sold in multiple transactions ranging from $103.88, to $104.75, inclusive. The price reported in Column 4 is a weighted average price. These shares were sold in multiple transactions ranging from $105.01 to $105.85, inclusive. The price reported in Column 4 is a weighted average price. These shares were sold in multiple transactions ranging from $$106.01 to $106.99, inclusive. The price reported in Column 4 is a weighted average price. These shares were sold in multiple transactions ranging from $107.01 to $108, inclusive. The price reported in Column 4 is a weighted average price. These shares were sold in multiple transactions ranging from $108.05 to $109.02, inclusive. The price reported in Column 4 is a weighted average price. These shares were sold in multiple transactions ranging from $111.20 to $112.97, inclusive. The price reported in Column 4 is a weighted average price. These shares were sold in multiple transactions ranging from $105.90 to $106.26, inclusive. /s/ William R. Gupp by power of attorney 2018-02-26