# Modified Bitumen (SBS or APP)

A modified bitumen membrane takes the qualities of a built-up system and combines them with the qualities of a single-ply roof — asphalt modified with polymers that change how it behaves in heat and cold.

**Provider:** Lloyd Roofing Company, Inc., Greenwood SC. Commercial and industrial only. 1-800-421-3830.

- **Modifiers:** SBS · APP
- **Application:** Torch · hot-mop · cold adhesive
- **Surfacing:** Granules · foil · coating

## What modified bitumen actually is

A modified bitumen membrane is composed primarily of polymer-modified bitumen reinforced with one or more plies of fabric — polyester, fiberglass, or a combination. Factory surfacing, where applied, includes mineral granules, slag, aluminum or copper.The waterproofing medium is traditional asphalt, modified with atactic polypropylene (APP), styrene-butadiene-styrene (SBS), synthetic rubber or other agents that enhance the asphalt's properties. APP and SBS are the most common modifiers.

## SBS versus APP

### SBS — Styrene-Butadiene-Styrene
SBS forms a polymer network within the bitumen, giving it rubber-like characteristics and improved resistance to aging and weathering. SBS sheets are set in hot mopping asphalt, torch-applied, or adhered with cold-process adhesives. Without factory granule or foil surfacing, they need a field-applied UV protective coating.
### APP — Atactic Polypropylene
A thermoplastic polymer that forms a uniform matrix within the asphalt. It increases UV resistance, improves flexibility at low temperatures, and improves flow resistance at high temperatures. APP sheets are generally applied with a propane torch: the heat softens the underside into a molten adhesive that flows onto the substrate and cools into a waterproof bond.

## The base sheet still matters

Modified bitumen systems are technically classed as single-ply, but Lloyd Roofing still installs a base sheet or underlayment beneath them — a 2-ply fiberglass platform minimum, or a 3-ply base, using standard glass-fiber felt, coated glass-fiber felt or coated organic felt.That base protects the system from water penetration and protects the insulation from the heat of the torch. For that reason we treat MBS as a built-up roof.

## Frequently asked questions

**Should I choose SBS or APP?**

SBS behaves like rubber and handles thermal movement and cold better. APP is a thermoplastic that resists UV and high-temperature flow better. Building movement, deck type and the climate of the site drive the choice.

**Is torch-applied roofing safe on an occupied building?**

Torch application requires strict fire-watch procedures and is not appropriate on every substrate. Where it isn't, SBS can be hot-mopped or set in cold-process adhesive instead — same membrane, no open flame.

**How is modified bitumen different from BUR?**

BUR builds waterproofing from multiple field-assembled plies of felt and bitumen. Modified bitumen delivers the waterproofing in a factory-made sheet with the polymer already blended in. Lloyd Roofing installs a base sheet under both.


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**Lloyd Roofing Company, Inc.** · 2415 Montague Avenue Ext., Greenwood, SC 29649 · 1-800-421-3830 · Mon–Thu 7:00am – 5:00pm · Fri 7:00am – 12:00pm
Commercial and industrial roofing only. Serving South Carolina, North Carolina and Georgia since 1965.
SC contractor license CLG10175 · USDOT 483661