Understanding Fire Retardant Treatment for Cedar Shakes
Cedar shakes have long been a popular roofing material, prized for their natural beauty, durability, and insulating properties. However, their organic composition makes them vulnerable to fire, which is a serious concern in wildfire-prone regions. Fire treating cedar shakes is an essential process that significantly improves their fire resistance, bringing them up to code in many jurisdictions. Unlike standard asphalt shingle options, cedar shakes require specialized treatment methods to meet building safety standards. This guide explores the approved techniques, chemical treatments, and application methods that property owners and builders need to understand.
Why Fire Treatment Matters for Wood Roofing
Wood roofing materials, including cedar shakes and shingles, carry a natural fire risk that building codes have addressed through specific standards. The Uniform Building Code (UBC) standard 32-7 sets the benchmark for fire-retardant-treated wood shakes and shingles. Roofs constructed with untreated cedar shakes can contribute to the rapid spread of fire, especially in dry climates where embers can ignite the wood surface. Fire treatment mitigates this risk by impregnating the wood fibers with chemicals that inhibit combustion. In regions with extended dry seasons, such as the western United States and Australia, building codes increasingly mandate fire rated roofing assemblies.
- Fire treated cedar shakes can achieve a Class A or Class B fire rating, depending on the treatment method and product specifications.
- Many local building codes in fire-prone areas now require fire-retardant-treated wood roofing materials.
- Insurance companies may offer reduced premiums for homes with fire-rated roofing systems that meet local code requirements.
- Properly treated cedar shake roofs contribute to the overall fire safety of the building structure and surrounding property.
The Science Behind Fire Retardant Chemicals
Fire retardant chemicals work through several mechanisms that disrupt the combustion process. When exposed to high heat, these chemicals undergo chemical reactions that reduce the flammability of the wood substrate. Common fire retardant compounds include ammonium phosphates, borates, and other mineral-based salts that create a protective barrier against ignition. The effectiveness of these chemicals depends on their ability to penetrate the wood structure and remain stable throughout the service life of the roofing material.
Diammonium Phosphate as a DIY Treatment Option
For those exploring do-it-yourself approaches, diammonium phosphate (DAP) has shown promising results in laboratory testing. The Texas Forest Products Laboratory has demonstrated that liberal applications of this chemical fertilizer dissolved in water can achieve the UBC minimum fire resistance rating. However, this approach has significant limitations that must be understood before implementation. The surface coating provided by DAP applications does not offer the same level of protection as industrial pressure treatment methods.
- Diammonium phosphate creates only a surface-level coating rather than a deep chemical bond within the wood fibers.
- The treatment is not permanent and requires reapplication, particularly after heavy rainfall or snow melt events.
- Monthly applications are recommended during fire season in high-risk areas to maintain adequate protection levels.
- The solution must be mixed to the correct concentration for optimal effectiveness and even coverage.
- Application requires careful attention to weather conditions, as rain immediately after treatment can wash away the chemicals.
Approved Fire Treating Methods and Standards
Not all fire treatment methods are created equal. Building codes recognize specific processes that have been rigorously tested and proven to provide reliable fire protection. Understanding these approved methods helps builders and homeowners make informed decisions about their roofing investments. When comparing different low slope roofing materials, fire treated cedar shakes offer a compelling balance of aesthetics and safety that few other roofing options can match.
The Full-Cell Vacuum-Pressure Process
The only permanent fire treating method recognized and approved by building codes is the full-cell vacuum-pressure process. This industrial treatment method is the gold standard for fire retardant wood products and is the same technology used in applications ranging from restoring cedar paneling to structural timber treatment for commercial buildings.
- Vacuum Phase: Cedar shakes and shingles are placed inside a sealed chamber where air is evacuated, creating a vacuum that pulls air out of the wood cells to prepare them for chemical absorption.
- Pressure Phase: Fire retardant chemicals are injected into the chamber under high pressure, typically ranging from 100 to 200 psi, forcing the treatment solution deep into the wood fibers.
- Recovery Phase: Excess chemical solution is removed from the chamber, and the treated shakes are dried to their final moisture content before packaging and shipment.
- Quality Testing: Each batch of treated shakes undergoes testing to verify that chemical retention levels meet the required specifications for code compliance.
Authorized Treatment Facilities and Quality Assurance
The Cedar Shake and Shingle Bureau has authorized several treating companies to perform the full-cell vacuum-pressure process using approved chemical formulations. These facilities follow strict quality control protocols to ensure consistent treatment results across all production batches. Homeowners and builders should verify that the cedar shakes they purchase come from an approved treatment facility to guarantee code compliance.
| Treatment Aspect | Full-Cell Vacuum-Pressure | DIY Surface Application |
|---|---|---|
| Chemical Penetration | Deep, throughout wood fibers | Surface level only |
| Permanence | Permanent treatment for roof life | Temporary, requires reapplication |
| Code Compliance | Meets UBC standard 32-7 | Marginal compliance only |
| Cost per Square | Higher initial investment | Lower upfront cost |
| Weather Resistance | Excellent, unaffected by rain | Poor, washes off over time |
| Fire Rating Achieved | Class A or B under standard testing | Class C or unrated |
| Warranty Coverage | Manufacturer warranty available | No warranty coverage |
Installation Considerations for Fire Treated Shakes
Installing fire treated cedar shakes requires careful attention to both the manufacturer specifications and local building code requirements. The treatment process can affect the physical properties of the wood, which in turn influences handling, cutting, and fastening methods. Builders who have experience with weaving sidewall shingles will find that roof shake installation follows similar principles but with additional considerations for fire rated assemblies and proper ventilation pathways.
Proper Handling and Storage
Fire treated cedar shakes should be stored in a dry, ventilated area before installation. The treatment chemicals can attract moisture if the bundles are exposed to rain or ground moisture, potentially causing dimensional changes and warping. Installers should handle the shakes with care to avoid damaging the treatment layer, particularly near exposed edges and ends where protection is most critical.
Fastening Requirements and Spacing
The fastening schedule for fire treated shakes follows similar patterns to untreated shakes, but with some important distinctions. Stainless steel or hot-dipped galvanized fasteners are recommended to prevent corrosion that could be accelerated by the treatment chemicals. The nail placement must ensure that each shake is securely attached while maintaining the integrity of the fire resistant barrier.
- Use approved corrosion resistant nails for all fastening points throughout the roof area.
- Maintain proper exposure based on the shake grade and roof slope for optimal weather shedding.
- Allow adequate spacing between shakes for thermal expansion and proper drainage during rain events.
- Follow the manufacturer guidelines for fastener placement and penetration depth into the roof deck.
Underlayment Considerations
The underlayment system beneath fire treated cedar shakes plays a critical role in the overall fire performance of the roof assembly. Many fire rated roof systems require specific underlayment products that have been tested and approved for use with fire treated wood shakes. Common options include self-adhered modified bitumen membranes and specially formulated roofing felts designed for fire rated assemblies.
Maintenance and Long-Term Performance
Fire treated cedar shakes require ongoing maintenance to preserve their fire resistant properties and structural integrity. Unlike some other roofing materials, the treatment does not eliminate the need for regular roof maintenance but does provide an additional layer of protection that can extend the service life of the roof significantly.
Inspection Schedule and Key Indicators
Regular inspections should be conducted at least twice per year and after any major weather event such as hailstorms or high winds. Homeowners and building inspectors should look for signs of treatment degradation, physical damage, or biological growth that could compromise the fire rating of the roof assembly.
- Check for cracked, split, or warped shakes that may expose untreated wood underneath the surface layer.
- Look for moss, algae, or fungal growth that can retain moisture and reduce fire resistance over time.
- Verify that replacement shakes used during repairs are also properly fire treated to the same specifications.
- Inspect flashing, valleys, and roof penetrations where fire protection continuity could be compromised.
- Monitor for any signs of chemical leaching or surface discoloration that might indicate treatment degradation.
When Reapplication or Replacement Is Needed
For factory treated shakes that have been installed correctly, the fire retardant treatment remains effective for the life of the roof under normal conditions. However, roofs that have experienced physical damage, improper installation, or exposure to harsh chemicals may require partial or complete replacement to maintain their fire rating. Professional roof inspectors can assess the condition of treated shakes and recommend appropriate remediation measures when necessary.
Fire treating cedar shakes is an investment in safety and code compliance that pays dividends in peace of mind. Whether choosing the industrial vacuum-pressure process or properly maintaining a treated roof over its service life, understanding the options and requirements helps ensure that your cedar shake roof provides both natural beauty and reliable fire protection for decades to come.