Modified Bitumen

What is a Modified Bitumen Roof?

Modified Bitumen is a roof product that is commonly comprised of a fiberglass scrim or inter-ply which is then coated on both sides with an asphalt based emulsion and the top surface is then coated with a mineral surface.  The emulsion is ‘modified’ with either a SBS or APP modifier which is a rubber or plastic based chemical which gives the membrane desirable attributes with respect to flexibility and its ability to withstand higher temperatures.

What are common uses of Modified Bitumen?

While these membrane can be applied to higher sloped roofs, these are typically installed on low sloped roofs. That is a roof with a pitch that is a minimum 1/4 inch per ft.  This type of roof is common for all types of houses and buildings and are often integrated into even tile and shingle roof systems for at least part of the building.  

What types of installations are available for Modified Bitumen?

There are 3 types of installations, a torch applied product, a self-adhered product and a liquid-style adhesive (cold process and hot asphalt) .  In both cases a base sheet is mechanically attached to the roof deck with nails.  With the torch applied product a propane fired torch is then used to ‘melt’ the membrane to the base sheet.  With the self-adhered product there is a factory applied adhesive with a slip sheet attached, which is removed, and the membrane is adhered to the base sheet.

What is a Flat Roof?  The Proper Terminology is Low-Sloped Roof.

A Flat Roof is actually called a low sloped roof.  That is a roof with a pitch that is a minimum 1/4 inch per ft and commonly used on structures with low sloped roof designs or porches and patios.  For roof slopes that are truly flat or don’t meet the minimum 1/4 inch per ft pitch, a tapered system design would be required to create the 1/4 inch per ft minimum to ensure properly water drainage off the roof.          

How long does this type of roof last?

There are many factors that determine a products longevity including how well the roof drains, weather and foot traffic on the roof.  But generally this type of roof will last between 13 and 16 years.

Is there anything that can be done to extend the life of this roof?

Yes, many times a customer will opt to coat the roof with an elastomeric coating.  The coating help to protect the membrane by blocking the damaging UV rays of the sun.  A side benefit is that after coating the roof it becomes highly reflective which helps lower the roof temperatures and ultimately increases the occupants comfort.  The roofs life can be extended for many, many years if it is coated prior to the membrane aging too much.

Is Roll Roofing the same thing as a Modified Bitumen membrane?

No, roll roofing does not have a modifier added to the emulsion and will not last nearly as long.  Additionally, Roll Roofing is installed by surface nailing the seams where the membrane overlaps and sealing the nail holes with roofing mastic.  Any time a roof product is penetrated by exposed nails the likelihood of leaks is present.  For this reason, Roll Roofing is not approved for livable areas or finished porches or patios where the underside has drywall installed.