Modified Bitumen in San Jose | Keith Roofing Company

Modified Bitumen San Jose

Modified Bitumen
Done Right Since 1952

Modified bitumen — 'mod-bit' to the trade — is an asphalt-based roll roofing modified with polymers for flexibility, durability, and weather resistance. Installed torch-on (heat-welded) or self-adhered, it's a workhorse commercial flat-roof system that's been standard for 40+ years. Keith Roofing has been installing mod-bit since it became widely available and we're certified installers for GAF, CertainTeed, Firestone, and Johns Manville mod-bit systems.

Mod-bit comes in two primary formulations. SBS (styrene-butadiene-styrene) is rubber-modified asphalt — flexible in cold temperatures, excellent recovery from deformation, typically self-adhered or hot-mopped. APP (atactic polypropylene) is plastic-modified asphalt — higher heat resistance, typically torch-applied. Both have 20-30+ year service lives with proper installation, both handle Bay Area climate well, and each has applications where it's the better choice.

Our mod-bit work includes: new mod-bit installation on new commercial construction; full replacement of aging BUR or other systems with mod-bit; mod-bit on low-slope residential applications (particularly Eichler homes and modern flat-roof residential); mod-bit repair and restoration work; and coordination with property managers and building owners on commercial portfolios.

Modified Bitumen project by Keith Roofing Company in San Jose

Complete Guide

Understanding Modified Bitumen Systems

SBS vs. APP: Choosing the Right Formulation

SBS mod-bit (styrene-butadiene-styrene) is the choice for most Bay Area commercial and residential flat-roof applications. SBS remains flexible across temperature ranges — doesn't stiffen in cold weather or soften excessively in summer heat. Typical application methods: self-adhered (peel-and-stick) or hot-mopped (traditional hot asphalt between plies). Self-adhered SBS is particularly popular for Eichler and residential low-slope applications where torch work isn't practical.

APP mod-bit (atactic polypropylene) is typically torch-applied — open-flame heating of the underside of the membrane as it's rolled into place. APP is more heat-resistant than SBS and preferred for some high-heat applications. Torch application requires specific safety protocols, trained operators, and insurance coverage for open-flame work.

Installation Methods

Torch-applied installation: traditional method for APP mod-bit. Propane torch heats the underside of the membrane as it's rolled into place, melting the modified bitumen into adhesive bond with the substrate. Requires trained operators, fire safety protocols, and site hot-work permits in many jurisdictions. Delivers strong bond but safety concerns mean many projects prefer alternatives.

Hot-mopped installation: traditional method using hot asphalt between plies (similar to BUR installation). Requires specialized equipment (kettles, asphalt transport) and trained crews. Delivers strong bond but declining in use due to equipment complexity.

Self-adhered installation: peel-and-stick membrane with factory-applied adhesive on underside. Significantly safer and simpler than torch or hot-mop methods. Typical choice for residential applications and increasingly common for commercial. SBS modifier works particularly well with self-adhered technology.

Cold-applied installation: liquid-applied cold adhesive between plies. Safer than torch or hot-mop but requires specific adhesive products and careful temperature-controlled application.

Common Applications

Mod-bit works well for: mid-size commercial buildings where a proven traditional system is preferred over newer single-ply; Eichler and mid-century modern residential flat/low-slope roofs (self-adhered SBS is particularly common); low-slope residential additions and modern flat-roof architecture; replacement of failing BUR systems where a similar traditional system is preferred; and high-heat applications favoring APP mod-bit.

When to Consider

Signs You Need
Modified Bitumen

Existing BUR System at End-of-Life

Aging BUR systems are commonly replaced with mod-bit for commercial applications. Similar installation approach, proven performance, and familiar maintenance.

Eichler Flat-Roof Re-Roof

Self-adhered SBS mod-bit is particularly well-suited to Eichler low-slope roof geometry. Avoids torch safety concerns on residential property.

Mid-Century Modern Residential Flat Roof

Mid-century architectural homes with low-slope or flat roof sections benefit from mod-bit durability and compatibility with the architectural style.

Modern Residential Flat-Roof Addition

New flat-roof residential architecture (modern and contemporary homes) works well with mod-bit — typically self-adhered for safety.

Commercial Project Preferring Traditional Systems

Some property owners prefer traditional systems over newer single-ply for perceived long-term reliability.

High-Wear or High-Heat Applications

Restaurant rooftops, industrial applications, or other high-wear environments can benefit from mod-bit's durability. APP formulation preferred for high-heat applications.

Mod-Bit Systems

Modified Bitumen
Options

GAF Mod-Bit Systems

Complete mod-bit product line including SBS and APP formulations, various base and cap sheets, self-adhered options.

CertainTeed Mod-Bit

Alternative mod-bit manufacturer with strong commercial and residential product lines.

Firestone Mod-Bit

Holcim-owned mod-bit systems with good Bay Area distribution.

Johns Manville Mod-Bit

Mod-bit products with solid Bay Area service network and competitive pricing.

Base Sheets

Modified asphalt base sheet material, mechanically-fastened or adhered foundation for mod-bit system.

Cap Sheets with Granule Surfacing

Mineral-surfaced cap sheets provide UV protection and aesthetic finish. Various colors available.

Our Process

How We Handle
Your Modified Bitumen

Existing Roof Assessment

For replacement projects, evaluation of existing roof condition, substrate integrity, drainage, and whether overlay or tear-off is appropriate.

System Specification

SBS vs. APP selection, application method (torch, hot-mop, self-adhered, or cold-applied), base sheet specification, and cap sheet selection.

Permit & Scheduling

Building permit, Title 24 compliance documentation. For torch-applied work, hot-work permit and safety protocols.

Installation

Tear-off or overlay preparation. Insulation installation where required. Base sheet, ply sheet installation via specified method. Cap sheet installation with granular surfacing.

Final Inspection & Warranty

Seam integrity verification. Flashing detail review. Manufacturer warranty registration and documentation package.

Why Keith Roofing

Why Homeowners Choose Us
for Modified Bitumen

All Mod-Bit Installation Methods

Torch-applied, hot-mopped, self-adhered, and cold-applied — we do all installation methods and recommend based on project specifics, not what's easiest for us.

Safety Culture for Torch Work

Torch applications require rigorous safety protocols. We maintain training, equipment, and insurance coverage for torch work and have excellent safety track record.

Eichler & Mid-Century Specialty

Significant portion of our residential mod-bit work is Eichler and mid-century modern homes — we know the architectural details and proper installation approach.

40+ Years of Mod-Bit Experience

Installed mod-bit since the material was introduced commercially. Pattern recognition on what works long-term vs. what fails prematurely.

Featured Project

1961 Eichler Home — Self-Adhered SBS Mod-Bit

Ponderosa, Sunnyvale

A 1961 Eichler in Sunnyvale's Ponderosa neighborhood had original 1990s mod-bit reaching end-of-life with multiple seam failures and ponding water in several areas. We specified Johns Manville self-adhered SBS mod-bit system with tapered polyiso insulation to address ponding issues. Installation used self-adhered method (no torch work — safer for residential property). Carefully detailed flashings at clerestory windows and atrium — common Eichler failure points. Project completed over 5 days with minimal homeowner disruption. 20-year manufacturer warranty registered. Expected service life: 25+ years with proper maintenance.

Common Questions

Modified Bitumen
Answered

SBS is rubber-modified — flexible across temperatures, preferred for Bay Area climate. APP is plastic-modified — more heat-resistant, typically torch-applied. Both have 20-30+ year service life.

With proper training, equipment, and safety protocols, yes. We maintain safety record through operator training, fire-watch protocols, and appropriate insurance. Self-adhered alternatives exist when torch work isn't desired.

20-30 years with proper installation and maintenance. Premium systems with enhanced warranties can extend this range.

Yes. Self-adhered SBS mod-bit is particularly well-suited to residential flat and low-slope applications. Common on Eichler and mid-century modern homes.

$7-$12 per square foot installed for most commercial applications. Residential applications (Eichler, modern flat roofs) run $10-$15 per square foot installed depending on complexity.

Yes. Mod-bit is well-suited to localized repair — seam restoration, patch repairs, flashing renewal all work well. Significant repair scope may favor coating or replacement.

Self-adhered eliminates open-flame safety concerns, simplifies installation, and works well for residential applications and buildings where torch-work permits are restrictive. Performance is comparable for most applications.

Residential Roofing

Commercial Roofing

South Bay

West Valley & Peninsula

San Jose

Modified Bitumen
Done Right Since 1952

Understanding Modified Bitumen Systems