Wood is particularly useful as a nailing base for different types of cladding and interior finishes. Wood furring strips can be used to attach interior finishes such as gypsum wallboard, provided:
- The strips are fastened to noncombustible backing or recessed into it
- The concealed space created by the wood elements is not more than 50mm thick
- The concealed space created by the wood elements is firestopped
Experience has shown that a lack of oxygen in these shallow concealed spaces prevents rapid development of fire.
Wood nailer strips can also be used on parapets, provided the facings and any roof membrane covering the facings are protected by sheet metal. This is permitted because it is considered that a nailing base such as plywood or oriented strandboard (OSB) does not constitute an undue fire hazard.