Exhibit 21
Simpson Manufacturing Co., Inc. and Subsidiaries
List of Subsidiaries of Simpson Manufacturing Co., Inc.
At February 28, 2013
1. Simpson Strong-Tie Company Inc., a California corporation
2. Simpson Strong-Tie International, Inc., a California corporation
3. Simpson Strong-Tie Canada, Limited, a Canadian corporation
4. Simpson Strong-Tie Europe EURL, a French corporation
5. Simpson Strong-Tie, S.A.S., a French corporation
6. Simpson Strong-Tie Japan, Inc., a California corporation
7. Simpson Strong-Tie Australia, Inc., a California corporation
8. Simpson Strong-Tie A/S, a Danish corporation
9. Simpson Strong-Tie GmbH, a German corporation
10. Simpson Strong-Tie Sp.z,o.o., a Polish corporation
11. Simpson France SCI, a French corporation
12. Simpson Strong-Tie Australia Pty Limited, an Australian corporation
13. Simpson Strong-Tie Mexico, S. de R.L. de C.V., a Mexican corporation
14. Simpson Strong-Tie Asia Limited, a Hong Kong company
15. Simpson Strong-Tie Asia Holding Limited, a Hong Kong company
16. Simpson Strong-Tie (Beijing) Company Limited, a Chinese company
17. Simpson Strong-Tie (Zhangjiagang) Co., Ltd., a Chinese company
18. Simpson Strong-Tie Ireland Limited, an Irish company
19. Ahorn-Geräte & Werkzeuge Vertriebs GmbH, a German company
20. Simpson Strong-Tie s.r.o., a Czech company
21. Societe Civile Immobiliere IMAG SCI, a French corporation
22. Socom S.A.S., a French corporation
23. Simpson Strong-Tie (New Zealand) Limited, a New Zealand company
24. Simpson Strong-Tie Switzerland GmbH, a Switzerland company
25. S&P Clever Reinforcement Company AG, a Switzerland company
26. S&P Handels GmbH, an Austrian company
27. S&P Clever Reinforcement GmbH, a Germany company
28. S&P Clever Reinforcement Company Benelux B.V., a Dutch company
29. S&P Polska Sp. z o.o., a Polish corporation
30. Clever Reinforcement Iberica — Materiais de Construção, Lda., a Portugal private limited liability company
31. S&P Reinforcement France, a French company
32. Simpson Strong-Tie (Thailand) Co., Ltd, a Thai company
33. Simpson Strong-Tie Vietnam Company Limited, a Vietnam company
34. Simpson Strong-Tie South Africa (PTY) Ltd, a South Africa company