Sec Form 3 Filing - Rudolph Jacob T. @ TREX CO INC - 2024-02-21

FORM 3 Check this box if no longer subject to Section 16. Form 4 or Form 5 obligations may continue. See Instruction 1(b).

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 STATEMENT OF CHANGES IN BENEFICIAL OWNERSHIP Filed pursuant to Section 16(a) of the Securities Exchange Act of 1934, Section 17(a) of the Public Utility Holding Company Act of 1935 or Section 30(h) of the Investment Company Act of 1940

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1. Name and Address of Reporting Person Rudolph Jacob T. 2. Issuer Name and Ticker or Trading Symbol TREX CO INC [ TREX] 5. Relationship of Reporting Person(s) to Issuer (Check all applicable) _____ Director _____ 10% Owner X __ Officer (give title below) _____ Other (specify below) SVP, CHRO (Last) (First) (Middle) 2500 TREX WAY, C/O TREX COMPANY, INC. 3. Date of Earliest Transaction (MM/DD/YY) 02/21/2024 (Street) WINCHESTER, VA22601 4. If Amendment, Date Original Filed (MM/DD/YY) 6. Individual or Joint/Group Filing (Check Applicable Line) __ X __ Form filed by One Reporting Person _____ Form filed by More than One Reporting Person (City) (State) (Zip)

Table I - Non-Derivative Securities Acquired, Disposed of, or Beneficially Owned 1.Title of Security (Instr. 3) 2. Transaction Date (MM/DD/YY) 2A. Deemed Execution Date, if any (MM/DD/YY) 3. Transaction Code (Instr. 8) 4. Securities Acquired (A) or Disposed of (D) (Instr. 3, 4 and 5) 5. Amount of Securities Beneficially Owned Following Reported Transaction(s) (Instr. 3 and 4) 6. Ownership Form: Direct (D) or Indirect (I) (Instr. 4) 7. Nature of Indirect Beneficial Ownership (Instr. 4) Code V Amount (A) or (D) Price Common Stock 43,439 ( 1 ) D

Table II - Derivative Securities Acquired, Disposed of, or Beneficially Owned ( e.g. , puts, calls, warrants, options, convertible securities) 1. Title of Derivative Security (Instr. 3) 2. Conversion or Exercise Price of Derivative Security 3. Transaction Date (MM/DD/YY) 3A. Deemed Execution Date, if any (MM/DD/YY) 4. Transaction Code (Instr. 8) 5. Number of Derivative Securities Acquired (A) or Disposed of (D) (Instr. 3, 4, and 5) 6. Date Exercisable and Expiration Date (MM/DD/YY) 7. Title and Amount of Underlying Securities (Instr. 3 and 4) 8. Price of Derivative Security (Instr. 5) 9. Number of Derivative Securities Beneficially Owned Following Reported Transaction(s) (Instr. 4) 10. Ownership Form of Derivative Security: Direct (D) or Indirect (I) (Instr. 4) 11. Nature of Indirect Beneficial Ownership (Instr. 4) Code V (A) (D) Date Exercisable Expiration Date Title Amount or Number of Shares Stock Appreciation Right $ 17.523 02/15/2020( 2 ) 02/15/2027 Common Stock 4,076 D Stock Appreciation Right $ 28.105 02/14/2021( 3 ) 02/14/2028 Common Stock 2,664 D Stock Appreciation Right $ 38.85 02/13/2022( 4 ) 02/13/2029 Common Stock 2,538 D Stock Appreciation Right $ 50.83 02/19/2023( 5 ) 02/19/2030 Common Stock 2,230 D Stock Appreciation Right $ 104.56 02/17/2024( 6 ) 02/17/2031 Common Stock 832 D Stock Appreciation Right $ 82.01 03/01/2023( 7 ) 02/23/2032 Common Stock 1,679 D Stock Appreciation Right $ 56.8 03/01/2024( 8 ) 02/14/2033 Common Stock 2,350 D Stock Appreciation Right $ 90.86 03/01/2025( 9 ) 02/19/2034 Common Stock 1,583 D

Reporting Owners Reporting Owner Name / Address Relationships Director 10% Owner Officer Other Rudolph Jacob T. 2500 TREX WAY C/O TREX COMPANY, INC. WINCHESTER, VA22601 SVP, CHRO Signatures /s/ Amy M. Fernandez by power of attorney 03/01/2024 Signature of Reporting Person Date

Explanation of Responses:

( 1 )Includes 1,415 time-based restricted stock units that vest March 1, 2024; 2,023 time-based restricted stock units that vest March 1, 2025; 1,482 time-based restricted stock units that vest March 1, 2026; 607 time-based restricted stock units that vest March 1, 2027; a target number of 2,021 performance-based restricted stock units that vest on March 1, 2024; a target number of 2,889 performance-based restricted stock units that vest on March 1, 2025; a target number of 2,118 performance-based restricted stock units that vest on March 1, 2026; and a target number of 867 performance-based restricted stock units that vest on March 1, 2027. The number of performance-based restricted stock units set forth above is the target number of shares. The number of shares that will actually vest will be based upon performance against certain financial goals for the Company, and will range from 0% to 200% of the target number of shares. ( 2 )This stock appreciation right became exercisable in three equal installments that occurred on February 15, 2018, February 15, 2019 and February 15, 2020. ( 3 )This stock appreciation right became exercisable in three equal installments that occurred on February 14, 2019, February 14, 2020 and February 14, 2021. ( 4 )This stock appreciation right became exercisable in three equal installments that occurred on February 13, 2020, February 13, 2021 and February 13, 2022. ( 5 )This stock appreciation right became exercisable in three equal installments that occurred on February 19, 2021, February 19, 2022 and February 19, 2023. ( 6 )This stock appreciation right became exercisable in three equal installments that occurred on February 17, 2022, February 17, 2023 and February 17, 2024. ( 7 )This stock appreciation right became exercisable in three equal installments, the first installment became exercisable on March 1, 2023, the second installment becomes exercisable on March 1, 2024 and the third installment will become exercisable on March 1, 2025. ( 8 )This stock appreciation right becomes exercisable in three equal installments occurring on March 1, 2024, March 1, 2025 and March 1, 2026. ( 9 )This stock appreciation right becomes exercisable in three equal installments occurring March 1, 2025, March 1, 2026 and March 1, 2027.

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* If the form is filed by more than one reporting person, see Instruction 4(b)(v).

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