Fire Safety and Reclaimed Wood: The Reality
One of the most common questions we receive from architects and builders is whether reclaimed lumber presents a greater fire risk than new wood. The short answer is no — in most applications, reclaimed lumber has the same fire performance as new lumber of equivalent species and dimension. But the longer answer involves important nuances about fire ratings, treatment options, and building code requirements that professionals need to understand.
Understanding Fire Ratings for Wood
Wood's fire performance is governed by two key metrics: flame spread index (FSI) and smoke development index (SDI), both measured through ASTM E84 (Standard Test Method for Surface Burning Characteristics of Building Materials) or the equivalent UL 723 tunnel test.
Most untreated domestic hardwoods and softwoods have a Class C flame spread rating (FSI of 76-200). Some dense hardwoods like white oak fall into Class B (FSI of 26-75). The building code prescribes maximum FSI values for different applications — for example, interior wall and ceiling finishes in most commercial occupancies must be Class B or better in exit corridors and Class C or better in other areas.
Does Reclaimed Status Affect Fire Performance?
The age and reclaimed status of lumber does not inherently change its fire performance. The flame spread characteristics of wood are determined primarily by species, density, and surface condition — not by whether the wood is new or old. In fact, old-growth reclaimed lumber often has higher density than new-growth equivalent species, which can result in slightly better fire performance (denser wood is harder to ignite and burns more slowly).
However, two factors unique to reclaimed wood require attention. First, if the reclaimed wood has an existing finish, paint, or coating from its previous use, that coating may affect fire test results. Old oil-based paints, varnishes, and shellac can increase flame spread. It is important to either strip old finishes or factor them into your fire rating assessment. Second, heavily weathered or degraded reclaimed wood with reduced density may not perform as well as sound wood of the same species.
Fire-Retardant Treatment Options
When the building code requires a fire rating that untreated wood cannot meet, fire-retardant treatment is available. There are two primary approaches:
Pressure-Treated Fire Retardant (PTFR)
Pressure-treated fire-retardant lumber has chemical fire retardants impregnated deep into the wood through a vacuum-pressure process. PTFR wood can achieve Class A flame spread ratings (FSI of 0-25), meeting the strictest interior finish requirements.
However, PTFR treatment is challenging for reclaimed lumber. The treatment process requires the wood to be at a specific moisture content, and the chemicals can alter the wood's appearance — often darkening it and reducing the visual character that makes reclaimed wood desirable. Most reclaimed wood applications avoid PTFR in favor of surface-applied alternatives.
Intumescent Coatings
Intumescent coatings are clear or tinted coatings that swell when exposed to heat, forming an insulating char layer that protects the wood underneath. Modern intumescent coatings are thin, clear, and can be applied like a conventional wood finish. They are the preferred fire protection method for reclaimed wood because they preserve the wood's appearance while providing Class A fire performance.
Products like No-Burn Original and Flame Stop can be applied by brush, roller, or spray and are compatible with most wood species. They add minimal cost — typically $1 to $3 per square foot of surface area — and can be topcoated with conventional finishes if desired.
Sprinkler Trade-Offs
In many commercial applications, the presence of an automatic sprinkler system allows less restrictive material requirements for interior finishes. In a fully sprinklered building, Class C materials may be used where Class B would otherwise be required. This provision can eliminate the need for fire-retardant treatment of reclaimed wood in many commercial interior applications.
Consult with your fire protection engineer and building code official early in the design process to determine whether your sprinkler system provides adequate trade-offs for your intended use of reclaimed wood.
Code Compliance Checklist for Reclaimed Wood
- Identify the occupancy type and applicable flame spread requirements from your local building code (typically IBC Chapter 8 for interior finishes).
- Determine the species of your reclaimed lumber and its baseline flame spread rating. Your lumber supplier should be able to provide species identification.
- Assess existing finishes on the reclaimed wood. Strip old finishes that may adversely affect fire performance, or test the material with the existing finish.
- Evaluate sprinkler trade-offs with your fire protection engineer.
- Specify fire-retardant treatment if required — intumescent coatings are the preferred method for reclaimed wood.
- Document everything for the plan review and inspection process. Inspectors may be unfamiliar with reclaimed wood and appreciate clear documentation of species, fire rating, and any treatment applied.
Our Support for Your Project
Norfolk Lumber can provide species identification, density testing, and documentation to support fire code compliance for reclaimed wood projects. We work regularly with architects, fire protection engineers, and building officials to ensure that reclaimed wood installations meet all applicable safety standards. Do not let fire code concerns prevent you from specifying reclaimed wood — with the right approach, compliance is straightforward.