Perished Felt: Understanding the Dangers and How Spray Foam Contributes to the Problem

Roofing felt plays a crucial role in protecting homes from the elements by providing a secondary barrier against moisture. However, when felt becomes "perished"—brittle, cracked, or damaged—it can no longer fulfil its function, leading to significant problems for homeowners. This issue is further exacerbated by spray foam insulation, which can accelerate the degradation of roofing felt.

In this article, we'll explore why perished felt is problematic and how spray foam insulation contributes to its deterioration.

Roofing felt is a protective layer installed beneath roof tiles or shingles. It is typically made of:

• Bitumen: A water-resistant material that prevents leaks.
• Fiberglass or polyester: Reinforcement to provide durability.

Its main purpose is to act as a secondary barrier, shielding the roof structure from water ingress, especially during heavy rain or when tiles are displaced.

When roofing felt deteriorates, it can no longer perform its essential functions. Perished felt can lead to:

1. Leaks and Water Damage
   Cracks or tears in the felt allow water to seep into the roof structure, leading to dampness, mold, and rot.
2. Weakened Roof Structure
   Prolonged exposure to moisture weakens wooden roof timbers, compromising the overall integrity of the roof.
3. Higher Repair Costs
   Perished felt often requires complete replacement, a costly and disruptive process that may involve stripping back tiles and other roofing materials.

​Spray foam insulation, while effective at improving energy efficiency, can accelerate the perishing of roofing felt in several ways:

1. Moisture Retention
   Spray foam creates an airtight seal, trapping moisture against the felt. Over time, this trapped moisture can cause the felt to deteriorate more quickly than it would under normal ventilation conditions.
2. Reduced Ventilation
   Proper ventilation is critical for preventing condensation and allowing the roof to "breathe." Spray foam insulation often restricts airflow, creating an environment where felt is more prone to decay.
3. Stress on Roofing Materials
   Closed-cell spray foam, in particular, expands and hardens, exerting pressure on the roof structure. This pressure can cause existing felt to crack or split, especially if the felt was already ageinga or poorly installed.
4. Hidden Damage
   Once spray foam is applied, it becomes nearly impossible to inspect the condition of the felt beneath. This can result in undetected issues that worsen over time, leading to costly repairs.

​Homeowners should watch for the following warning signs:

• Leaks or water stains inside the property, especially after heavy rainfall.
• Dampness or mold growth in the loft or attic.
• Sagging or uneven roof sections, which may indicate structural issues.
• Cracked, torn, or brittle felt visible during a roof inspection.

If you notice any of these signs, it's essential to address the issue promptly to prevent further damage.

​Perished felt poses serious risks to the integrity of your roof and the overall safety of your home. While spray foam insulation may seem like an effective energy-saving solution, it can accelerate the deterioration of roofing felt by trapping moisture, restricting airflow, and masking hidden damage.

At Countrywide, we specialize in identifying and addressing issues related to roofing felt and spray foam insulation. If you suspect your roof felt is perished or are considering insulation options, reach out to us for expert advice and solutions tailored to your needs.

Protect your roof, protect your home. Trust the experts to guide you every step of the way.