Flat Roofing

polyglass torch on bitumen with a non-prorated manufacturer's warranty which covers materials and workmanship. 

plywood base is applied then all air-conditioning units

are raise to apply polyglass triply underneath to seal

We pioneered the use heat-welded APP modified bitumen for flat roofs in Southern California in the 1980s. When installing APP systems, Paragon uses absolutely no mastic (aka Henry's, plastic roof cement, etc.); every penetration through the roof is sealed with multiple layers of the roofing membrane itself. This significantly reduces the opportunities for leaks and the cost of maintenance over the roof's service life.



Flat Roofs: Built-up roofing vs. heat-welded APP modified bitumen


[Note: This section does not cover rubber or plastic roof systems. While they are excellent products, they're also easy to puncture, making them impractical for roofs which experience moderate-to-high levels of foot traffic from multiple vendors such as HOAs, strip malls, industrial or factory buildings, etc. They are also significantly more expensive than either built-up or APP modified systems.]


The maxim "the devil is in the detail" is extremely accurate when it comes to flat roofs. For most customers, there are two practical choices for covering flat roofs: built-up roofing (BUR) systems and modified bitumen.




BURs (aka "hot mop" or "hot tar") have been used for more than a century. They

consist of alternating layers of asphalt-impregnated paper and liquid asphalt applied via mop; this also requires the use of a large asphalt kettle throughout the course of installation.


In addition to the fumes from the kettle present during application, it's critical that a sufficient amount of asphalt is applied between layers of paper and that the asphalt is at least 400° F when the next layer of paper is embedded into it. (Otherwise, it will not properly bond.)


Because the asphalt begins to cool very quickly after it has been mopped into place, a standard rule of thumb is that the person rolling the paper out into the asphalt should be no further than five feet behind the person mopping-down the liquid asphalt.


Other variables such as the ambient temperature at the time work is performed and the quality of the liquid asphalt (in regard to the amount of key polymers and resins which make it both waterproof and flexible) further complicate the installation of a durable, long-lasting BUR system.


Additionally, there is the issue of sealing penetrations through the roof such as sump drains, scuppers, vents, pipes, electrical conduit, HVAC ducts, etc. With a BUR, the only way these can be made watertight is the use of mastic (aka Henry's, plastic roof cement, etc.).


Mastic is not a very durable material. Standard mastics dry-out and start to become brittle within 12-18 months after application; modified mastics will last approximately twice that long.


As it becomes brittle, mastic can no longer accommodate normal building movement such as thermal cycling (i.e., warm days, cool nights) and settling. This means that every roof component sealed with mastic will be an ongoing maintenance item for the roof's service life. As such, inspections and application of additional mastic will be required every 2-3 years.


Modified bitumen


"Modified" roofing is also an asphalt-based product but is superior to a BUR.


It's a single-ply sheet and the asphalt is very carefully formulated in regard to the polymers and resins which make asphalt a good roofing material. The sheet has a polyester scrim embedded in it, which adds significant tensile strength - the ability to stretch without tearing - and puncture resistance.


The term "modified" refers to ensuring a precise blend of key chemicals compared with the varying amounts present in raw asphalt, thus "modifying" it. Both the asphalt blending and manufacturing of the sheet are done to extremely precise tolerances, yielding a very consistent product.


There are two main types of modified roofing. The designations "SBS" and "APP" refer to the specific polymer blends in the asphalt used to manufacture the sheets.)


• SBS modified, which is applied with liquid asphalt. It is subject to many of the same problems as BURs, such as the proper temperature and amount of asphalt as well as the fact all penetrations require the use of mastic to seal them. It is also critical to remove all air bubbles after the sheet has been rolled-out but before the temperature

of the asphalt drops below 400° F.


• APP modified, which is applied via heat-welding and requires a much higher level of workmanship. A properly-installed APP system also provides significant advantages over SBS systems:


1) Absolutely no mastic is required. All penetrations through the roof are sealed with multiple layers of the membrane itself (along with a metal flashing). As a result, all of the penetrations are included in the Manufacturer's warranty; this is not generally the case with SBS systems.


Given that these penetrations are all potential points of failure (i.e., leaks) due to building movement, lack of regular maintenance, seismic events, etc., an APP system is far more robust over the roof's service-life. This is particularly important in regard to sump drains and scuppers, given the volume of water they must accommodate during even a moderate rain.


2) Heat-welding permits extremely precise control of the application temperature; the membrane is heated as it is rolled out so there is almost no heat loss during application. This means both excellent adhesion and the elimination of any air trapped beneath the material.


Additionally, after a course of the membrane has been applied, the seam between it and the previously applied course is gently pulled back, reheated and then carefully troweled-out to ensure proper outflow of asphalt and a durable, watertight bond between adjacent sheets.


Proper heat-welding also provides superior long term adhesion at critical junctures such as Z-bar on stucco walls, along the outside edges of parapets. Where edge metal is required, it is both nailed and "sandwiched" between two layers of modified. This is particularly important along gutters; even if a gutter and/or downspout becomes completely clogged, it is nearly impossible for water to get beneath the edge of the roof.


(You can find links to materials data sheets and technical drawings under the "Manufacturers" heading.)


Heat-welded APP modified systems represent about 80% of our annual sales each year; very few of our competitors can equal our expertise in applying them.