Frequently
Asked Questions

The More You Know About
Roofing Options, the Better
We Can Serve You

Over the years, these are some of the topics our customers have asked about regarding common roofing issues, the techniques we use, and the various materials involved in delivering a hand crafted roofing solution. If you have questions that aren't answered here, call or email us.


1. What are the most common causes of roof leaks?

The most common causes of roof leaks are blisters, pressure ridges, bare felts and ponding of water.


2. What is B.U.R., and how does it work?

Built-Up Roofing (commonly known as “asphalt and gravel” or composition roofing) is the most reliable approach for commercial / industrial flat roof applications. It was invented in England, where it rains a LOT, in the 1840s and while the materials and technology have evolved, the basic premise remains the same.

There are 3 basic components in a B.U.R. system -- waterproofing, reinforcing and surfacing – which are either secured using hot asphalt or torch-applied:

- Waterproofing keeps you dry.

- Reinforcing ensures maximum structural integrity.

- Surfacing (most often done with a top coat of asphalt covered with UV-reflecting aggregate or mineral) keeps the underlying structure protected from water, light and wind. Surfacing is also known as ballasting.


3. What materials are used in B.U.R.?

4-ply B.U.R. Systems are typically comprised of 15lb perforated felts and sometimes fiberglass reinforced felts, laminated together with hot asphalt and finished with 3/8's pea gravel ballast.

Depending on your existing building structure, specific climate related-needs and the extent of your repair requirements, there are a wide range of B.U.R. systems and products Crown Industrial may employ in various combinations to ensure a secure, dry roof over your head. The most common options used in B.U.R. systems are:

Modified Bitumen Membrane (MB)
Polymer-modified bitumen or modified bitumen (MB) sheet membranes were developed in Europe in the early 1960s and have been in use in North America since the mid 1970s. Polymer-modified roof membranes are composed of reinforcing fabrics that serve as carriers for the hot polymer-modified bitumen as it is manufactured into a roll material. MB roof system membranes are composed of multiple layers, much like B.U.R. membranes. MB roof systems typically are installed as a two-ply system and almost always are fully adhered. There are two types of MB roofing membranes:

- SBS (Styrene-butadiene-styrene aka “elastic asphalt”)
SBS polymer-modified bitumen membranes commonly are installed in hot moppings of asphalt (similar to B.U.R. systems) or cold adhesive. Some SBS modified membranes have an adhesive backing and are self-adhering.

- APP (Atactic polypropylene aka “plastic asphalt”)
APP polymer-modified bitumen membranes typically are heat-welded or torch-applied. Generally, APP modifiers impart a "plasticized" quality to asphalt, and SBS modifiers impart a "rubberized" quality to asphalt. MB membranes and EPDM, a thermoset membrane, often are confused by consumers because roofing contractors aren't always clear in explaining the differences. MB and EPDM membranes are sometimes called "rubber roofs." Surfacings for MB membranes include aggregate or gravel, mineral surfacing, metal foil-laminate surfacing and smooth liquid-applied surfacing.


4. What are Single-Ply Systems?

A. Thermoset Membranes

Thermoset membranes are made of materials that chemically crosslink. Once the seams have cured your roof is essentially comprised of one giant sheet of roofing over your head and possessions. Thermoset membrane options include:

- EPDM (Ethylene propylene diene terpolymer)

- CSPE (Chlorosulfonated polyethylene)

- ECH (Epichlorohydrin)

- CR (Neoprene)

- PIB (Polyisobutylene)

B. Thermoplastic Membranes

These membranes are very similar to thermosets but there is no chemical cross-linking or vulcanization. Seams in the materials are welded together with solvents or heat. The welds - when done properly - are as strong as the material itself. The most common types of hermoplastic membranes are:

- PVC (Polyvinyl chloride)

- PVC alloys & compounds

- CPE (Chlorinated polyethylene)

- TPO (Thermoplastic olefin)