Modified bitumen membranes are typically used for roof waterproofing in a two-ply

application. The plies of rolled sheets can be bonded by using hot asphalt or fused by

torching the mating surfaces together with a hot flame. Cold applications can be done by

use of Cold Adhesive or by Self Adhesive(Peel Stick) application.


The most prevalent system design using modified bitumen utilizes the membrane in a

fully exposed condition. The membrane is used on occasion in the inverted design or

protected system as well. Modified bitumen is formulated using either Atactic

Polypropylene(APP) or Styrene Butadiene Styrene(SBS) modifiers in combination

with asphalt. The SBS membranes have better low-temperature flexibility and are most common in Canada Modified bitumen membranes are manufactured in rolled reinforced sheets

approximately I meter in width and thickness of 2.2, 2.5, 3, and 4 millimeters

The reinforcement for modified bitumen sheets is either fiberglass or non-woven 

polyester. Manufacturers' designations 90, 100, 180, 250, refer to the reinforcement

weight in grams per square meter.


The mopping surface of modified bitumen sheets is sanded while the surface

of the torch grade sheets is a thermo-fusible plastic film. The application is usually done in

two layers, a base sheet, which has no granule protection on the topside, and a cap

sheet, which does have granule protection on the top



Advantages and Disadvantages



PRIMARY ADVANTAGES of modified bitumen membranes are

1. Excellent flexibility

2. High strength

3. High puncture resistance

4. Year-round application (cold process applications are restricted to +5 degree C)

5. Variety of colors

6. Lightweight

7. Excellent weathering



PRIMARY DISADVANTAGES of modified bitumen membranes are

1. Fire hazards (Torch grade)

2. Poor solvent resistance

Ethylene-Propylene-Diene-Monomer (EPDM)