The two ply roofing system is a durable low-slope roofing solution commonly used in commercial and some residential buildings. This article explains the different types, materials, installation steps, costs, life expectancy, performance characteristics, and maintenance best practices to help readers evaluate suitability and long-term value. Key advantages include enhanced waterproofing, redundancy, and improved longevity compared with single-layer systems.
Aspect | Quick Summary |
---|---|
Common Types | Built-Up Roofing (BUR) and Modified Bitumen (SBS, APP) |
Typical Lifespan | 15–35 Years Depending On Materials And Maintenance |
Average Cost | $3.50–$8.50 Per Sq Ft Installed (Varies Widely) |
Best For | Low-Slope Commercial Roofs, Some Residential Flat Roofs |
What Is A Two Ply Roofing System?
A two ply roofing system uses two principal membrane layers to create a continuous waterproof barrier over a roof deck. The layers are typically either asphalt-based or polymer-modified, stacked to provide redundancy and improved resistance to water infiltration. Two ply systems aim to combine adhesion, puncture resistance, and UV protection through layered construction.
Common Types Of Two Ply Roofing
Built-Up Roofing (BUR) – Two Ply Variations
Built-up roofing traditionally involves alternating layers of bitumen (hot-applied asphalt or cold adhesives) and reinforcing felts. A two ply BUR uses two layers of felt or ply sheets, which are often finished with gravel or a surfacing coating for UV and physical protection. BUR is proven for heavy foot traffic and provides reliable redundancy through multiple embedded felts.
Modified Bitumen Membranes
Modified bitumen membranes come in two main modifiers: Styrene-Butadiene-Styrene (SBS) for elasticity and Atactic Polypropylene (APP) for plastic-like durability. A two ply modified bitumen roof typically consists of a base ply and a cap ply installed by torching, cold adhesive, or self-adhered methods. SBS offers better low-temperature flexibility; APP can deliver stronger UV and oxidation resistance when surfaced properly.
TPO Or EPDM Hybrid Approaches
While true two-ply TPO or EPDM is less common, some systems combine a base polymer sheet with a second protective membrane or coverboard. These hybrids leverage the benefits of thermoplastic or rubber membranes plus an additional layer to improve durability and redundancy. Hybrid two-ply approaches are used when designers want polymer performance with added protection.
Materials Used In Two Ply Systems
The primary materials include asphalt or modified bitumen sheets, reinforcement felts, adhesives (cold-applied or hot asphalt), and surfacing options such as gravel, coatings, or reflective membranes. Quality of the bitumen modifier, membrane thickness, and surfacing plays a central role in system performance and lifespan.
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- Base Ply: Reinforced felt or polymer-modified sheet that provides structural waterproofing.
- Cap Ply: Surface ply optimized for UV, traffic, and weather resistance.
- Adhesives/Asphalt: Bonding agents critical for layer adhesion and seam integrity.
- Surfacing: Gravel, reflective coating, or granulated cap sheet to protect from UV and mechanical wear.
Installation Process And Best Practices
Proper installation is essential to realize the performance of a two ply roofing system. Key stages include substrate preparation, vapor control, insulation, base ply installation, cap ply application, and surfacing or flashing details. Seam quality, flashings at penetrations, and moisture control during installation are decisive for long-term success.
- Inspect And Prepare Deck: Ensure a stable, dry substrate; remove contaminants and repair deck irregularities.
- Install Vapor Retarder And Insulation: Use appropriate vapor control to prevent trapped moisture; secure insulation to avoid deflection.
- Apply Base Ply: Use hot asphalt, cold adhesive, or torch methods per manufacturer guidelines to ensure full adhesion and seam overlap.
- Install Cap Ply: Ensure proper heat or adhesion technique; seams must be sealed and rolled to eliminate voids.
- Finish Flashings And Surfacing: Detail all drains, curbs, and penetrations; protect membrane with gravel or reflective coating where specified.
Benefits And Performance Characteristics
Two ply roofing systems deliver redundancy, improved puncture resistance, and often better long-term waterproofing than single-ply alternatives. They are widely used where low-slope geometry increases ponding risk. Two ply systems can reduce the likelihood of immediate major failures because a breach in one ply may not compromise the secondary barrier.
- Redundancy: Secondary layer helps prevent leaks after single-ply damage.
- Puncture And Traffic Resistance: Thicker composite reduces risk from foot traffic and equipment.
- Customizable Surfacing: Options include ballast, coatings, or granules for UV protection.
- Repairability: Damaged areas can often be patched or relayed without full replacement.
Costs And Expected Lifespan
Installed costs for two ply roofing vary by membrane type, substrate, insulation needs, and geographic labor rates. Typical national ranges are $3.50–$8.50 per square foot, with higher-end systems or complex details costing more. Lifespan typically falls between 15 and 35 years depending on material quality, installation, exposure, and maintenance.
Factors Affecting Cost And Life: membrane type (SBS vs APP vs BUR), thickness of plies, type of surfacing, roof slope, rooftop equipment, and local permitting or fire code requirements. Preventive maintenance can extend service life significantly.
Maintenance, Inspection, And Common Repairs
Regular inspection and timely repairs are crucial to maximize life expectancy. Recommended inspections occur twice yearly and after major weather events. Typical maintenance actions include clearing drains, repairing blisters, sealing seams, and recoating surfacing where applicable. Early detection of ponding, seam separation, or flashing failures prevents small defects from becoming costly leaks.
- Routine Checks: Look for ponding water, membrane splits, seam fail, and flashing integrity.
- Minor Repairs: Patch small holes or seam gaps with compatible membrane and adhesive.
- Major Rehabilitation: Consider overlaying with new ply or full replacement if multiple failures or extensive deterioration exist.
Energy Performance And Building Code Considerations
Two ply roofs can support reflective coatings and cool roof strategies to reduce heat gain and HVAC loads. Adding light-colored surfacing or reflective coatings improves energy efficiency and can qualify for local incentives. Compliance with local building codes, fire ratings, and energy code (IECC) requirements should guide material choice and installation details.
Insulation thickness and thermal bridging affect R-value. When pursuing energy upgrades, designers should evaluate load capacity for added insulation and potential need for tapered systems to improve drainage.
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Environmental And Sustainability Factors
Many two ply systems use asphalt-derived materials that can be recycled or reclaimed in some programs, though recycling availability varies regionally. Choosing high-reflectance surfacing or incorporating vegetative roof toppings can improve sustainability metrics. Specifying recycled content insulation, cool coatings, and planned maintenance reduces life-cycle environmental impacts.
How To Choose A Contractor And What To Ask
Selecting an experienced roofing contractor is fundamental to a successful two ply system. Verify manufacturer certifications, local references, warranty offerings, and detailed scope of work. Key questions include warranty terms, installation method (torch, hot asphalt, cold adhesive), substrate preparation, and how they handle unforeseen conditions.
- Request Proof Of Insurance And Licensing.
- Ask For Manufacturer-Endorsed Warranties And Project-Specific Details.
- Get A Written Scope That Defines Material Brands, Ply Counts, And Surfacing.
Common Pitfalls And How To Avoid Them
Frequent problems include improper deck preparation, insufficient vapor control, poor seam welding, and inadequate flashing. Avoid these by following manufacturer specifications, using certified installers, and documenting inspections during and after installation. Because moisture trapped under plies accelerates failure, vapor management and dry substrate are critical.
Cost Comparison: Two Ply Vs Single Ply
Feature | Two Ply | Single Ply |
---|---|---|
Redundancy | High | Lower |
Initial Cost | Moderate–High | Lower–Moderate |
Repair Complexity | Moderate | Simple Patching |
Lifespan Potential | Longer With Proper Care | Variable |
Frequently Asked Questions
Is Two Ply Roofing Suitable For Residential Homes?
Two ply systems are best suited to low-slope residential roofs such as flat additions or modern architectural designs. Traditional steep-slope homes generally use shingles or metal roofing instead. When a residential roof has minimal slope or frequent ponding, two ply offers superior waterproofing.
Can Two Ply Roofs Be Repaired Instead Of Replaced?
Yes, many two ply issues are repairable, including localized seam failures or punctures. However, extensive degradation or multiple failed layers may necessitate replacement or overlay. Periodic maintenance reduces the chance of large-scale replacement.
Are Two Ply Systems Fire-Rated?
Fire ratings depend on materials and installation methods. APP torch-applied systems and hot asphalt installations may have specific fire considerations. Always consult local code and the membrane manufacturer’s fire classification. Proper installation and adherence to fire codes are essential to achieve required ratings.
Resources And Further Reading
Consult membrane manufacturers, NRCA (National Roofing Contractors Association), local building codes, and energy code resources for technical guides and specification templates. Manufacturer technical data sheets and NRCA installation manuals provide authoritative guidance for design and maintenance.
If a project is imminent, gathering competitive bids, reviewing warranty specifics, and scheduling a pre-installation inspection will reduce surprises and ensure the two ply roofing system performs as intended.
How to Get the Best Roofing Quotes
- Prioritize Workmanship
A roof is one of your home’s most important investments. Always choose a contractor based on experience and reputation — not just price. Poor installation can lead to expensive problems down the road. - Compare Multiple Estimates
Don’t settle for the first quote you receive. It’s always a smart move to compare at least three bids from local roofing professionals. You can 877-801-4315 to get local quotes from roofing contractors in your area, available across the United States. - Use Negotiation Tactics
After selecting a trusted roofer, be sure to use our proven tips — How to Negotiate with Roofing Contractors — to secure the best possible final price without cutting corners.