Is there a difference between PWF and Pressure Treated Wood? YES! Permanent Wood Foundation (PWF) material is pressure treated wood, but not all pressure treated wood can be used for PWF materials. All lumber and plywood used in a PWF must be pressure treated with Chromated Copper Arsenate (CCA) wood preservative. PWF material will be identified with a certification mark stating conformance with CSA Standard 0322, Procedure for Use in Preserved Wood Foundations. Most home improvement retailers do not stock PWF material. Before you begin your PWF, make sure you’re working with the correct product. Whether you’re building a home, an extension, or if you’ve purchased a home with a PWF, rest assured that this form of construction is durable, comfortable, adaptable, energy efficient and economical.