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Materials & Specificationsaka: PT lumberaka: FRTWaka: fire retardant treated wood

Treated Lumber

In Plain English

Lumber treated with chemicals to resist specific hazards like rot, insects, or fire.

Definition

Treated lumber is wood that has been processed with preservative chemicals, fire retardants, or other treatments to enhance its performance in specific applications. Pressure treated lumber resists decay and insects. Fire-retardant treated lumber (FRTW) is used where the building code requires non-combustible construction but wood is permitted.

Why It Matters in Bidding

Treated lumber carries a price premium over untreated material and is non-substitutable where code requires it, so estimators must read framing notes carefully to price pressure-treated sills, ledgers, and fire-retardant members correctly. Confusing FRTW with standard PT, or missing where treated material is mandated at concrete contact, creates either an overbid or a rejected submittal and costly rework.

Example

Taking off an exterior deck and wall plates on a podium structure, an estimator prices pressure-treated sill plates at all concrete contact and fire-retardant treated blocking where the spec calls for FRTW in the rated assembly.

Related Terms

Pressure Treated LumberDimensional LumberSoftwoodBuilding Code

Frequently Asked Questions

Code generally requires preservative-treated or naturally durable wood wherever framing contacts concrete, masonry, or the ground, and in exposed exterior applications prone to moisture. Common spots include sill plates, ledgers against masonry, and posts near grade. Estimators should flag every such interface so the premium material is captured in the takeoff.
Pressure-treated lumber resists decay and insects for moisture-exposed locations. Fire-retardant treated wood is chemically treated to slow flame spread and is permitted in certain assemblies where the code would otherwise require non-combustible construction. They are not interchangeable, and each must match the assembly and rating the documents specify.
Yes. Many preservative chemicals are corrosive, so codes and manufacturers require hot-dipped galvanized or stainless fasteners and connectors rated for treated wood contact. Estimators should price the upgraded hardware alongside the lumber, since ordinary fasteners can fail prematurely and trigger structural connector replacement under warranty.

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