Fire-Retardant Treatment for Cedar Roof Shakes and Shingles

Introduction to Fire-Retardant Cedar Roofing

Cedar shakes and shingles have been a popular roofing material for centuries, valued for their natural beauty, insulating properties, and durability. However, the flammability of untreated cedar has become an increasing concern as wildfires have grown. Cedar shakes and shingles have been a popular…, more frequent and intense in many regions. Fire-retardant treatment technologies have evolved to address this vulnerability, allowing property owners to enjoy the aesthetic benefits of cedar roofing while meeting modern fire safety standards.

The demand for fire-retardant-treated cedar has grown significantly as building codes in fire-prone areas have become more stringent. Understanding the available. The demand for fire-retardant-treated cedar has grown s

Two primary methods exist for treating cedar shakes and shingles with fire retardant: the full-cell vacuum-pressure process. Two primary methods exist for treating cedar shakes…, and surface-applied chemical treatments. These methods differ substantially in their effectiveness, permanence, and cost.

for treating cedar shakes and shingles with fire retardant: the full-cell vacuum-pressure process and surface-applied chemical treatmentsFire Protection High Rise Buildings. These methods differ substantially in their effectiveness, permanence, and cost.

The only permanent fire-retardant treatment recognized and approved by building codes (UBC Standard 32-7) is the full-cell vacuum-pressure process. This industrial. The only permanent fire-retardant treatment recognized and approved…, t

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The Full-Cell Vacuum-Pressure Process
The only permanent fire-retardant treatment recognized and approved by building codes (UBC Standard 32-7)Fire Resistance Ratings is the full-cell vacuum-pressure process. This industrial treatment forces fire-retardant chemicals dee

The process works by sealing shakes and shingles inside a treatment chamber. A vacuum is created within the chamber, drawing air and moisture out of the wood cells. Fire-retardant chemicals are then introduced under pressureFire Safety, forcing the solution deep into the wood structure. The pressure is maintained until the chemical has f

Several treatment companies have been authorized by the Cedar Shake and Shingle Bureau to perform this processFire Retardants Construction. These authorized treaters follow standardized procedures that ensure consistent quality and documented code compliance.

until the chemical has fully penetrated the cedar cells. After treatment, the shakes are dried before packaging and shipment.

Several treatment companies have been authorized by the Cedar Shake and Shingle Bureau to perform this process. These authorized treaters follow standardized procedures that ensure consistent quality and documented code compliance.

DIY Surface Treatment Options

For those who have access to untreated shakes at a lower cost and wish to apply fire retardant themselves, surface-applied treatments are available. The Texas Forest Products Laboratory has found that liberal applications of diammonium phosphate (DAP)—a common chemical fertilizer—dissolved in water can achieve the minimum fire-resistance rating required by UBC standards.

The DAP solution is sprayed or brushed onto the shakes, penetrating the surface layers to provide a degree of fire protection. However, this treatment is not permanent. Unlike the full-cell vacuum-pressure process, surface-applied treatments remain vulnerable to weathering, UV degradation, and wash-off from rain. The treatment must be reapplied at regular intervals to maintain its effectiveness.

For roofs in fire-prone areas, researchers recommend monthly applications of DAP solution during the fire season. This frequency is impractical for most property owners, which is why permanent factory-applied treatments are strongly preferred for permanent installations.

Fire Performance Comparison

Treatment Method	Process	Permanence	Code Approval	Relative Cost
Full-cell vacuum-pressure	Chemicals forced into wood under vacuum and pressure	Permanent (lifetime of the shingle)	UBC Standard 32-7 approved	Higher

Treatment	Flame Spread Rating	Time to Ignition (minutes)	Heat Release Rate (kW/m²)	Treatment Longevity
Untreated cedar shake	Class C or unrated	5-8	120-180	N/A
Vacuum-pressure treated	Class A or B	20-30+	40-60	Lifetime
DAP surface treated (fresh)	Class B	12-18	60-90	30-90 days
DAP surface treated (weathered 6 months)	Class C	6-10	100-140	Expired

Building Code Requirements

Building codes in wildfire-prone areas typically require that roof coverings have a minimum Class B fire rating, and in the highest risk areas, Class A is required. Untreated cedar shakes generally carry a Class C rating at best, which may not satisfy current code requirements in many western states.

The Uniform Building Code (UBC) Standard 32-7 specifically addresses fire-retardant-treated wood shakes and shingles. This standard defines the testing protocols and performance criteria that treated cedar must meet to achieve code compliance. Only the full-cell vacuum-pressure process has been recognized as producing permanent, code-compliant results under this standard.

Code officials in fire-prone jurisdictions will typically require documentation of the treatment process and certification that the installed shakes meet the applicable fire rating requirements. Retaining treatment certificates and manufacturer documentation is essential for passing final inspections and for insurance purposes.

Cost Considerations

The cost difference between treated and untreated cedar shakes is significant but must be weighed against the value of code compliance, insurance savings, and fire safety. Vacuum-pressure-treated shakes typically cost 25 to 40 percent more than untreated shakes. However, this premium is generally less than the cost of installing untreated shakes and then retrofitting a fire-rated roof covering if code requirements change or insurance carriers demand upgraded coverage.

Insurance premiums in fire-prone areas increasingly reflect the fire rating of the roof covering. Property owners with fire-retardant-treated cedar roofs may qualify for reduced premiums compared to those with untreated wood roofs. Some insurers refuse to write policies for properties with untreated wood roofs in high-risk fire zones.

Installation Considerations

Fire-retardant-treated cedar shakes install similarly to untreated shakes, with a few important considerations. Treated shakes may be slightly more brittle than untreated material, requiring care during handling and nailing. Stainless steel or hot-dipped galvanized fasteners are recommended to prevent corrosion from potential chemical reactions with the fire retardant.

The underlying roof deck and underlayment must also meet fire-resistance requirements for the complete roof assembly to achieve its rated classification. Fire-retardant-treated shakes installed over an inadequate substrate may not perform as intended in a fire event. Consult the manufacturer’s installation instructions and local code requirements for complete assembly specifications.

Conclusion

Fire-retardant treatment makes cedar shakes and shingles a viable roofing option even in areas with stringent fire codes. The full-cell vacuum-pressure process provides permanent, code-compliant fire protection that preserves the natural beauty of cedar while meeting modern safety standards. While DIY surface treatments can provide temporary fire resistance, they require ongoing maintenance and do not offer the same level of code compliance or peace of mind as professionally treated products.