Fasteners & Treated Wood
Conrad Forest Products always recommends the use of hot-dipped zinc-coated galvanized steel, stainless steel, silicon bronze or copper fasteners with all pressure-preservative or fire-retardant treated wood products.
The coating weight weights for zinc-coated fasteners shall be in accordance with ASTM A-153. Stainless steel fasteners shall be type 304 or 306.
The Model Building Codes (now known as the International Building Code – IBC and International Residential Code IRC) have developed sets of standards for every component of building construction. These have evolved over the years based upon both laboratory and actual field-testing provided by the material manufacturers.
The Building Code definition for TREATED WOOD is:
"Wood impregnated under pressure with compounds that reduce their susceptibility to flame spread or to deterioration caused by fungi, insects, or marine borers."
Further, the Building Codes adopted the American Wood-Preservers Association (AWPA) C Standards and M4 as their STANDARDS OF QUALITY for “Preservative treatment by pressure process and quality control. The 2006 Standards, when adopted, now reference AWPA U1 and M4.
The Building Codes do not make any reference or allowance for brand names or the chemical acronyms for wood preservative treatments. The following are the exact excerpts from the 2003 and 2006 Codes for fasteners and treated wood:
2003 & 2006 International Residential Code – Fasteners – Section R319.3
“Fasteners for pressure-preservative and fire-retardant-treated wood shall be of hot-dipped galvanized steel, stainless steel, silicon bronze or copper. Exception: One-half inch (12.7mm) diameter or greater steel bolts.”
2003 & 2006 International Building Code – Fasteners – Section 2304.9.5
“Fasteners for pressure-preservative treated wood shall be of hot-dipped galvanized steel, stainless steel, silicon bronze or copper. Coating weights for zinc-coated fasteners shall be in accordance with ASTM A-153.
Exception: Fasteners other than nails, timber rivets, wood screws and lag screws shall be permitted to be of mechanically deposited zinc coated steel with coating weights in accordance with ASTM B-695, Class 55 minimum.
Fasteners for treated wood foundation systems shall be as required in AF&PA Technical Report No. 7.
“Fasteners in preservative-treated wood shall be approved silicon bronze or copper, stainless steel or hot-dipped zinc-coated steel. Zinc coated fasteners shall be coated after manufacture to their final form, including pointing, heating, threading or twisting, as applicable.”
The Building Codes mandate (not suggest) the use of treated wood in various applications – inside and outside wood frame structures. The Building Codes are specific – as shown above – in the requirement for types (not manufacturer’s brands) of fasteners and connectors used in both treated and non-treated wood construction.
The rational for the mandate on treated wood and proper fasteners – to preserve and protect the primary structural components of wood frame construction throughout the life expectancy of the structure.
The following are the fastener recommendations from preservative suppliers: