HomeMy WebLinkAboutPolymeric Based Building Products in Wildfire Resiliency Code 07.29.2026
July 15, 2026
RE: Polymeric Exterior Products Association (PEPA) and the Fenestration
and Glazing Industry Alliance (FGIA), July 10, 2026 letter: Opposition to the Ban on Polymeric
Building Products
Dear Pitkin County Commissioners,
Pitkin County appreciates PEPA and FGIA's support for advancing wildfire resilience and
recognizes that many polymeric building products have successfully demonstrated compliance
with nationally recognized testing standards under specific laboratory conditions. However, the
County respectfully disagrees that its local amendments are inconsistent with the intent of the
Colorado Wildfire Resiliency Code (CWRC) or that they unnecessarily prohibit otherwise
code-compliant building products.
The CWRC establishes a minimum statewide standard intended to provide a baseline level of
wildfire protection across a broad range of communities and wildfire hazards. Importantly, the
code expressly preserves the authority of local jurisdictions to adopt more restrictive provisions
where warranted by local conditions. Pitkin County's amendments reflect its unique combination
of steep topography, dense wildland fuels, frequent wind-driven fire conditions, and limited
evacuation routes. Collectively, these factors support a more conservative approach to structural
hardening than the statewide minimum requirements.
While PEPA and FGIA correctly note that certain polymeric products may be incorporated into
wall assemblies that achieve ASTM E119 fire-resistance ratings, those test results should not be
interpreted as representative of wildfire performance. ASTM E119 evaluates the fire resistance
of a complete wall assembly under controlled furnace conditions and is intended to measure the
duration that an assembly maintains its structural integrity when exposed to a standardized
interior fire. It does not evaluate the performance of exposed exterior materials subjected to
radiant heat, direct flame impingement, wind-driven embers, or prolonged wildfire exposure.
Consequently, a one-hour fire-resistance rating should not be construed as evidence that all
individual components remain intact or provide equivalent performance during a wildland fire.
530 E. Main Street, Suite 205, Aspen, CO 81611
During the County's code amendment process, staff reviewed available research on the
performance of exterior building materials under wildfire conditions. That research found that
vinyl and other polymer-based products used for siding, windows, doors, and fencing adjacent to
structures generally do not maintain their protective function when exposed to the extreme
radiant heat and direct flame conditions characteristic of wildfires. Research conducted by the
National Institute of Standards and Technology (NIST) has demonstrated that vinyl can melt,
shrink, and pull away from the wall assembly, exposing combustible substrates and increasing
the potential for ember intrusion and flame penetration. NIST has also documented that the
thermal decomposition and combustion of PVC-based products can release hazardous
combustion products, including hydrogen chloride and carbon monoxide. While these materials
may perform acceptably under conventional building fire scenarios, their behavior during
prolonged exterior wildfire exposure differs significantly from the conditions represented by
standardized laboratory testing.
The County's restrictions on polymeric window frames are similarly based on long-term wildfire
resilience rather than state minimum code compliance. Post-fire investigations and wildfire
research have consistently identified windows as one of the most vulnerable components of the
building envelope. Although glazing failure often initiates assembly failure, elevated
temperatures can also soften or deform polymeric frames, potentially compromising weather
seals, reducing frame rigidity, and increasing the likelihood of ember intrusion following glazing
breakage. Additionally, warping and deformation can contribute to glazing failure.
Noncombustible framing materials provide an additional layer of passive protection by
maintaining greater structural stability under prolonged heat exposure and reducing reliance on
the performance of individual components during extreme fire events.
Similarly, the County's prohibition on polymeric fencing immediately adjacent to structures is
intended to reduce opportunities for fire spread. Numerous wildfire mitigation organizations,
including CAL FIRE and the University of California Fire Network, recommend replacing
combustible fencing with noncombustible materials in the area immediately surrounding
structures because attached fencing can serve as a pathway for flame spread to the primary
building. Polymer fencing may also soften, deform, or fail under wildfire exposure, diminishing
its effectiveness as a protective barrier and potentially creating additional hazards during
emergency response operations.
It is also important to distinguish between state minimum code compliance and risk reduction.
The CWRC permits many products that satisfy prescribed testing criteria; however, compliance
with a minimum standard does not preclude a jurisdiction from adopting more protective
measures where justified by local conditions. Pitkin County has intentionally reduced the use of
combustible exterior materials wherever practical to improve overall community resilience and
reduce the likelihood of structure ignition during extreme wildfire events. Similar local
amendments have been adopted by jurisdictions throughout Colorado and the western United
States where wildfire hazards exceed those contemplated by minimum statewide standards.
530 E. Main Street, Suite 205, Aspen, CO 81611
Finally, the County's amendments should be viewed as one component of a comprehensive
wildfire mitigation strategy rather than as isolated material restrictions. The limitations on
combustible exterior products complement requirements for ignition-resistant construction,
ember-resistant detailing, defensible space, and noncombustible zones immediately adjacent to
structures. Collectively, these measures create multiple layers of protection, reduce dependence
on any single building component, and improve the overall resilience of structures exposed to
severe wildfire conditions.
For these reasons, Pitkin County believes its local amendments are supported by available
scientific research, justified by the County's unique wildfire risk profile, consistent with the
authority granted to local governments under Colorado law, and represent a reasonable exercise
of the County's responsibility to protect life, property, critical infrastructure, and the long-term
resilience of its communities.
Below is a list of scientific citations that support our research:
NIST Technical Note 2304 – documents vinyl siding melting, shrinking, and loss of fire-barrier
function.
NIST firebrand exposure studies (Manzello et al.) – demonstrates ember-driven ignition and
failure of vinyl siding assemblies.
CAL FIRE Home Hardening Guide – recommends noncombustible fencing adjacent to
structures to reduce fire spread.
University of California ANR Fire Network – identifies vinyl fencing as susceptible to melting
and recommends noncombustible materials near homes.
University of California ANR Fire Network - identifies vinyl windows deformed as a result of a
radiant exposure from neighboring home that had ignited and was ultimately destroyed.
Insurance Institute for Business & Home Safety (IBHS) Wildfire Prepared Home guidance –
emphasizes noncombustible materials and the importance of the first five feet around structures.
Fire Safety Research Institute, UL Research Institutes - investigates window frame failure modes
during exterior fire exposure. Vinyl assemblies had both the largest number of sash failures and
contributed the most to out-of-plane stress on glass panes
University of Maryland / NIST Window Fire Testing - concludes that vinyl-frame windows did
not perform well under the exposure of imposed heat fluxes. Vinyl frames and sashes lost
strength, distorted and sagged, permitting openings to develop.
NIST Technical Note 2153- documents that vinyl window frames can soften and deform when
exposed to elevated radiant heat, potentially releasing the glazing and creating an opening
through which embers or flames may enter the structure. While glazing failure is often the
530 E. Main Street, Suite 205, Aspen, CO 81611
initiating event, maintaining the integrity of the window frame under prolonged thermal
exposure is an important component of wildfire-resistant construction.
Sincerely,
Jeffrey Erickson,
Chief Building Official
Jeffrey H. Woodruff
Pitkin County Board of County Commissioners, Board Chair
530 E. Main Street, Suite 205, Aspen, CO 81611