A contractor's insight

Editor's note: Following are the author's opinions. Views expressed are not necessarily those of NRCA.

This month, I originally had intended to provide some guidelines explaining the process by which FM Global engineers decide whether submitted roof systems are "Approved" or "Accepted." However, it appears FM doesn't want to provide that type of information to those of us who submit new/replacement/re-cover projects for review. The FM engineer who originally had volunteered to help with this article suddenly had his responsibilities changed and his "time" was so limited that participation in this type of article became impossible. It might lead one to believe FM's "Approvals" and "Acceptance" of roof systems are more subjective than FM would like us to know.

So lacking a clear (or any) direction, we as an industry are left to muddle through our dealings with FM as best we can.

RoofNav, etc.

RoofNav was supposed to be in Beta testing by this time, but so far, there is no indication RoofNav is anywhere close to being completed despite major emphasis on development of the program by FM. It is encouraging FM hired an outside consultant from the roofing industry to help put the final touches on RoofNav; perhaps that will put a more practical spin on the end product.

You should know FM Property Loss Prevention Data Sheets 1-28, "Design Wind Loads"; 1-29, "Above-Deck Roof Components"; and 1-31, "Metal Roof Systems," have been revised and Data Sheet 1-7 has been "deemed obsolete" and no longer should be considered applicable. Because Data Sheet 1-7 addressed "Wind Forces on Buildings and Other Structures," one can't help but wonder whether the weather gods have changed their methods of influence on wind forces in our lives.

According to FM correspondence dated October 2002, the only "revisions" to Data Sheets 1-28 and 1-29 were "Revised Title." For the paltry sum of $75, you can update your FM titles to these data sheets. Data Sheet 1-31 needed a lot of help, so a $75 fee might be worth it to determine just how much help FM provided in the revised data sheet (though you shouldn't get your hopes too high). But for a limited time, you can have all three revised data sheets for only $75—an obvious bargain too good to pass up. If you call in the next 10 minutes, FM might throw in a revised order form!

Substrates

Stick around this industry long enough, and old friends revisit. Remember GRM? The Grace Roof Membrane (GRM), for newcomers in our midst, was a take-off on a Bituthene waterproofing membrane "specially formulated" to provide a roof membrane. The Bituthene waterproofing system was a proven performer that generally performed its intended function reasonably well. GRM didn't fare as well and eventually was phased out (nobody ever withdraws a roofing product from the market).

The self-adhered bituminous roof membrane concept is back with multiple entries from multiple sources. Self-adhered sheets are made "sticky" by the introduction of special process oils to SBS-modified asphalt. The sticky surfaces typically are covered with a release paper that is removed as the self-adhered membrane is applied. In the past, it generally was recommended a self-adhered membrane be rolled with heavy rollers immediately following placement to ensure positive contact with the substrate over which it was installed. Installation guidelines for new self-adhered products have yet to be well-defined.

The attraction to self-adhered roof membranes is obvious: They suffer no volatile organic compound-related problems; no special equipment is required for installation; no odors during installation are experienced (primers don't "smell"); no skilled labor is required for installation; and they can be installed in one ply. (It seems we haven't yet learned the value of base sheets and backer sheets for system redundance.)

Nobody wants to talk about the truckloads of release paper to dispose of following installation of self-adhered roof membranes. Or the safety issues concerning the roof mechanic who has to pull the release paper off the roll while walking backward off the roof edge. Or the problem of compensating for a "curl" in a sheet induced during manufacture and the side lap eventually running to below minimum width. Or the fact that once a self-adhered membrane solidly is in place, there is no room for adjustment. Or the problems associated with end laps and "T" laps in the membrane. Or the fact that special surface preparation of substrates usually is necessary and all available substrates are not suitable for direct installation of self-adhered membranes.

There have been minimal advances in technology in the "oiled" SBS business, so the installation problems common to the first self-adhered roof membranes remain the principal challenges for applicators. The configuration of self-adhered sheets may have changed, and some (such as mineral granule- or metal foil-faced sheets) will be substantially more difficult to handle than the smooth Tedlar® or polyethylene film surface of the old GRM!

For instance, Dens Deck® Prime may provide a good substrate for self-adhered roof membranes because the top surface of the gypsum board is sealed with a proprietary coating and the glass fibers in the facer essentially are encapsulated in the coating. Even multiple coats of asphalt primer couldn't make the surface of regular Dens Deck suitable for installation of a self-adhered roof membrane because natural voids in the fiberglass mat facer would not allow uniform bonding of the self-adhered roof membrane to the primed, regular Dens Deck surface.

Perlite and some types of wood/cane fiber roof insulation will be challenging for contractors to provide suitable substrates for self-adhered bituminous roof membranes.

Polyisocyanurate foam roof insulation boards may be suitable substrates for self-adhered roof membranes depending on the boards' facer compositions. Some special preparation may be necessary with some polyisocyanurate foam roof insulation to be suitable substrates for self-adhered roof membranes. The key to this application will be the use of small (48- by 48-inch [1219- by 1219-mm]) boards and positive mechanical attachment of polyisocyanurate foam insulation substrate. Any upward "curling" of inadequately secured edges of the polyisocyanurate foam roof insulation will result in delamination of the self-adhered roof membrane making it susceptible to "peel" under high wind forces.

Base sheets

Now, let's talk about suitable base sheets. Virtually all fiberglass-reinforced base sheets are manufactured with sand parting agents. Sand becomes a parting agent when it is applied to a sheet during manufacture, and sand isn't smart enough to know that its role changes when the base sheet roll is set in place as an intended substrate for self-adhered roof membranes. Even polymer-modified asphalt base sheets will come with some type of parting agent on their surfaces, which means some special attention must be paid to virtually all base sheets to make them suitable substrates for self-adhered roof membranes.

Mechanically fastened base sheets will be included as substrates for self-adhered roof membranes by any prudent manufacturer for applications over wood, cementitious wood fiber and/or lightweight insulating concrete roof decks. Therefore, a suitable preparation of included base sheets must be prescribed by roof membrane purveyors.

Laps

The Achilles heel of self-adhered roof membranes has been and will continue to be the formation of laps—both side and end. Neither Tedlar nor the surface polyethlene sheet on GRM provided good bonding surfaces—they were too "slick." It doesn't appear likely anyone will reintroduce polyethylene or Tedlar surfaces for the new lines of self-adhered roof membranes, but mineral granule and metal foil surfaces will present even greater challenges for applicators and/or manufacturers. Mineral granules and metal foil must be removed from end-lap or flashing-lap areas to allow a bitumen-to-bitumen bond. Even if manufacturers are able to provide rolls with selvage ends, there still will be times when rolls are cut and a selvage end goes in one direction or another.

EPDM suppliers have developed (after one or two dismal generations) self-adhered seam tapes that have performed admirably for many years. But priming of the mated surfaces is a critical step in the success of seam tapes. It may well be that the current line of self-adhered bituminous roof membranes will require some special treatment at side laps and end laps to ensure satisfactory long-term lap performance.

End-lap formation will be the major challenge during application of a self-adhered roof membrane system because the adjacent rolls overlap each other and form a mass, or pile, of polymer-modified asphalt membrane. The thicker the membrane, the greater the challenge in sealing the end-lap junctures because the thicker sheets will "bridge" and not conform readily at the end-lap junctures. Additional system sealants may be required at "T" laps. Staggering end laps will be essential in the application process.

Other issues

And how might the current self-adhered bituminous roof membrane systems fare under wind uplift? That will depend on the integrity of the substrate over which a roof membrane is installed, appropriate preparation of the substrate and how well the self-adhered membrane can bond to the substrate surface. In prior attempts to promote self-adhered bituminous roof membranes, heavy rollers were used to ensure as much adhesion as possible was acquired in the application process. It will be interesting to see how metal foil-faced, self-adhered bituminous roof membranes tolerate what may be necessary embedment techniques.

Flashing of self-adhered bituminous roof membrane systems also will present a challenge because a flashing membrane must be positively tied onto a roof membrane's surface. How well a tie-in performs depends on the surfacing and juncture treatment at the roof membrane surface.

A polymer-modified asphalt backer sheet could be installed and the self-adhered roof membrane could run continuously up vertical surfaces as a starter sheet at roof perimeters. But we still must address flashing membranes at roof penetrations, and varying flashing heights may make elimination of separate flashing sheets impossible. And what about treatment of interior and exterior flashing corners?

Outwardly, the self-adhered bituminous roof membrane system appears to be a simple concept. But selection of system components, selection and preparation of substrates, special provisions for formation of side laps and end laps, membrane flashing installation and juncture treatment make this outwardly simple system much more complex. Self-adhered bituminous sheets will not stick to just anything—even themselves in select instances.

It looks as if the learning curve for the manufacture and installation of self-adhered bituminous roof membrane systems is just beginning—again.

We continue to see blister-related problems when hot-applied roof membrane systems are installed over Dens Deck substrates. Remember, Dens Deck initially may contain acceptable quantities of moisture, but when stored under humid environmental conditions, Dens Deck may absorb enough ambient moisture to cause blistering of solidly adhered base sheets or ply sheets. Dens Deck is moisture-resistant, not moisture-proof. Perforated venting base sheets should be considered as the initial ply for hot-applied membrane roof systems installed over Dens Deck or other gypsum-type thermal barriers.

Dick Baxter is president of CRS Inc., Monroe, N.C.