Torch-on Roofing Felt Guide: Benefits, Installation, and Maintenance

Torch-on roofing felt is a popular choice for low-slope and flat roofs across the United States due to its durability and waterproofing performance. This guide explains what torch-on roofing felt is, compares product types, outlines installation steps, highlights safety best practices, and offers maintenance tips to help property owners and contractors make informed decisions. Key Takeaways: long-lasting waterproofing, requires professional installation, and regular inspections extend service life.

Aspect	What To Know
Material	Bitumen-based sheets with a torch-applied adhesive
Best Use	Low-slope and flat roofs, balconies, roof decks
Lifespan	15–50 years depending on membrane type and maintenance
Installation	Heat-applied by certified professionals; safety precautions required

What Is Torch-On Roofing Felt?

Torch-on roofing felt, also called torch-applied membrane or modified bitumen roofing, consists of fiberglass or polyester reinforcement saturated with bitumen and surfaced with mineral granules or smooth finishes. During installation, the underside of the sheet is heated with a propane torch to melt the bitumen and bond the membrane to the substrate. This method creates a continuous, monolithic waterproof layer that resists ponding water and wind uplift.

Types Of Torch-On Roofing Felt

Several formulations exist, and choosing the right one affects performance, longevity, and cost. The common types include APP (Atactic Polypropylene) and SBS (Styrene-Butadiene-Styrene) modified bitumen. APP behaves like plastic, offering UV resistance and dimensional stability, while SBS provides rubber-like flexibility and cold-weather performance. Choosing APP or SBS depends on climate, roof movement, and project budget.

APP Modified Bitumen

APP membranes are often finished with mineral granules or aluminum to increase UV resistance. They are suitable for hot, sunny climates because they resist heat-related deformation. APP is preferred for roofs with minimal thermal cycling and where reflectivity is desired.

SBS Modified Bitumen

SBS membranes are more elastic and perform better in freezing temperatures and on roofs that experience movement from thermal expansion. They adhere well at lower temperatures and are commonly used in temperate to cold regions. SBS offers superior flexibility and crack resistance compared with APP.

Benefits Of Torch-On Roofing Felt

Torch-on roofing felt provides several advantages over built-up roofing and some single-ply systems. Key benefits include superior waterproofing, strong seam bonding, good puncture resistance, and long term durability when properly installed. For flat and low-slope roofs, torch-applied membranes deliver reliable protection against leaks and standing water.

• Durability: Thick membrane layers and reinforcement provide resistance to foot traffic and mechanical damage.
• Seam Strength: Heat-welded seams create continuous waterproofing with fewer vulnerable joints.
• UV Options: Granules or reflective coatings can improve UV resistance and energy performance.
• Repairability: Localized repairs are straightforward with patching techniques and compatible materials.

Where Torch-On Roofing Felt Is Best Used

Torch-on membranes are ideal for commercial buildings, multi-family residences, garages, and some residential flat roofs. They work well for balconies, parapet walls, and roof terraces where water management is critical. Designers often specify torch-on felt for roofs with low slope (typically less than 3:12) where reliable ponding water resistance is required.

Installation Process Overview

Professional installation is essential due to the use of open flame and the need for proper substrate preparation. The process typically includes substrate cleaning, primer application, layout of membranes, torch bonding, seam welding, and flashing details. Certified roofing contractors follow manufacturer instructions and local codes to ensure a safe, watertight installation.

1. Inspection And Preparation: Remove debris, repair substrate defects, and ensure a dry, clean surface.
2. Primer Application: Apply primer where specified to improve adhesion.
3. Membrane Positioning: Roll out sheets and align overlaps per manufacturer recommendations.
4. Torch Bonding: Use a propane torch to heat the underside until the bitumen melts and bonds to the substrate.
5. Seam Welding: Overlap edges and use torch heat to create sealed, fused seams.
6. Flashing And Details: Properly torch and seal around penetrations, drains, and parapets for continuous waterproofing.

Safety And Code Considerations

Torch applications carry fire risks, so jurisdictions may require permits, fire watch procedures, fire-resistant barriers, and trained installers. Building codes and insurance carriers can impose restrictions or require alternative methods such as cold adhesives or self-adhesive membranes. Contractors must follow OSHA guidelines, local fire codes, and manufacturer safety instructions to minimize hazards.

Common Safety Measures

• Obtain permits and notify local authorities when required.
• Use fire blankets, extinguishers, and a designated fire watch during and after torching.
• Protect combustible materials and maintain clearance from vents, insulation, and wooden structures.
• Employ trained personnel with appropriate PPE and torch equipment safety features.

Maintenance Best Practices

Routine inspections and proactive maintenance extend the life of torch-on roofing felt. Regular checks after storms and semi-annual inspections will help detect seam failures, punctures, or areas of delamination. Early detection and timely repairs prevent minor issues from becoming expensive leaks and structural damage.

• Visual Inspections: Look for blisters, splits, granule loss, or loose flashing.
• Drainage Maintenance: Keep drains and scuppers clear to avoid ponding water.
• Repair Small Damages: Patch punctures and reseal seams with compatible bitumen patch or manufacturer-recommended products.
• Professional Surveys: Schedule periodic professional assessments, including infrared or moisture scanning if warranted.

Costs And Lifespan Expectations

Initial installation costs for torch-on roofing felt are typically higher than simple single-ply systems due to labor intensity and installer expertise. However, lifecycle costs can be competitive given the membrane’s longevity and low maintenance when properly installed. Typical service life ranges from 15 to 50 years depending on membrane type, climate, installation quality, and maintenance.

Factor	Impact On Lifespan
Membrane Type	SBS generally lasts longer in cold climates; APP performs well in hot, sunny areas
Installation Quality	Poor installation reduces lifespan significantly; professional installation is critical
Maintenance	Regular inspections and repairs extend expected life
UV Exposure	High UV accelerates aging unless protective coatings or granules are used

Common Problems And How To Address Them

Torch-on roofing felt can experience specific issues such as blisters, seam failures, and thermal cracking. Understanding causes helps guide repairs and preventive measures. Addressing root causes—poor drainage, inadequate flashings, or thermal movement—prevents recurring problems.

• Blisters: Caused by trapped moisture or air. Repair by puncturing and relaying a bonded patch or replacing the section.
• Seam Failures: Often due to improper torching or dirt at junctions. Re-weld seams or replace overlapping sections with correct technique.
• Punctures And Tears: Patch with compatible bitumen and reinforcement; inspect for underlying substrate damage.

Alternatives To Torch-On Roofing Felt

There are alternatives that avoid open flame, including self-adhesive modified bitumen, cold-applied liquid membranes, and single-ply systems like TPO and PVC. Each option has trade-offs in cost, durability, and performance. Self-adhesive membranes reduce fire risk, while single-ply systems can offer ease of installation and factory warranties.

Choosing A Contractor And Product

Select contractors with experience specifically in torch-applied membranes and verify certifications, references, and insurance coverage. Request product data sheets, warranties, and examples of similar completed projects. Choosing the right membrane manufacturer and a certified installer increases the likelihood of a durable, problem-free roof.

• Verify installer certification and local licensing.
• Ask for written warranties covering materials and workmanship.
• Request references and photos of past projects in similar climates.
• Confirm that fire safety protocols and permits were followed on prior jobs.

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Resources And Further Reading

Trusted sources include manufacturer technical datasheets, roofing trade organizations such as NRCA, and local building code resources. Consulting product-specific installation guides and safety bulletins provides the most accurate application details. Professionals should always follow manufacturer guidelines and local regulations when specifying and installing torch-on roofing felt.

For questions about compatibility, warranty, or project-specific concerns, contacting manufacturers and certified contractors ensures compliance and performance.