Exhibit 21

Simpson Manufacturing Co., Inc. and Subsidiaries

List of Subsidiaries of Simpson Manufacturing Co., Inc.

At February 28, 2012

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 Reinforcement International AG, a Switzerland company
27.	S&P Handels GmbH, an Austrian company
28.	S&P Clever Reinforcement GmbH, a Germany company
29.	S&P Clever Reinforcement Company Benelux B.V., a Dutch company
30.	S&P Reinforcement Sp. z o.o., a Polish corporation
31.	Clever Reinforcement Iberica — Materiais de Construção, Lda., a Portugal private limited liability company