The not-so-new self-adhered roof membrane

In the rush to provide environmentally friendly, nontoxic, odorless, colorless, tasteless, benign, harmless, cheap, super-reflective energy-efficient roof membrane materials, self-adhered bituminous and nonbituminous roof membranes are being reintroduced to the roofing marketplace. The concept is not new; the first self-adhered roof membrane systems date back almost 30 years. There have been some relatively modest improvements and modifications to old formulations, but the basic self-adhered roof membrane properties remain essentially the same—they stick to their substrates without extraneous adhesives.

The material

Original self-adhered roof membrane systems were produced from asphalts altered with polymer modifiers. Plastic films were applied to top surfaces of the membranes and parting sheets to the bottoms. As a material roll was set in place, the release/parting paper on the bottom side of the sheet was removed to expose the sticky bottom side of the membrane. To ensure continuous contact of the sticky bottom side with the substrate, lawn rollers were used to press the membrane into place. Various surfacings were used to protect the ultraviolet- (UV-) sensitive waterproofing material from exposure.

The "new" self-adhered roof membrane systems come in two varieties—bituminous and polymeric. Various surfacing materials or UV stabilizers are factory-included and replace the original plastic films and field-applied surfacings. But parting sheets remain on the bottom sides of the sheets to be removed in the field. As a material roll is set in place, the release/parting paper on the bottom side of the sheet is removed to expose the sticky bottom side of the membrane. To ensure continuous contact of the sticky bottom side with the substrate, rollers are recommended to press the membrane into place. Various surfacings/stabilizers are being used to protect the UV-sensitive waterproofing material from exposure. Notice any similarities?

Self-adhered roof membranes are, by their very nature, more expensive to produce than "normal" roofing materials—whether they are bituminous- or polymer-based membranes. Asphalt modifiers and parting sheets add to the cost of self-adhered sheets, and the pressure-sensitive self-adhered backers on nonbituminous roof membranes may cost more than the sheet itself without consideration of the inclusion of the parting sheet. The additional cost to produce self-adhered sheets is ostensibly offset by the no-longer-necessary adhesives used to bond traditional membranes to substrates.

There always is hype about resultant "labor savings" to be realized with self-adhered roof membrane systems, but the savings are terribly elusive in anything but exceptional installations. Installation of self-adhered roof membrane systems often requires diligence well above and beyond the level of care necessary for installation of more traditional, redundant and more forgiving roof membrane systems.

Self-adhered bituminous membranes have gained ever-increasing acceptance as underlayment materials for steep-slope roof systems. The underlayment sheets are not intended to provide "waterproofing" under steep-slope watershedding roof systems, but they are essentially self-healing around fastener penetrations and provide sufficient waterproofing properties to minimize ice damage and water damage at unheated overhangs and valley areas. Consequently, underlayment wrinkles caused by moisture absorption into the felt that telegraph through shingle units are minimized. Self-adhered underlayment membranes also provide more waterproofing protection for water-sensitive substrates because laps are sealed and self-adhered underlayment sheets are not susceptible to wind displacement before shingle installation.

Installation

The self-adhering properties of all self-adhered roof membranes directly are affected by ambient temperature at the time of application, moisture accumulation on substrates, surface conditions of substrates and whether the membrane comes under full sun load shortly after installation.

Installation of any presently available self-adhered roof or flashing membranes in cold temperatures may result in unsatisfactory performance of the finished roof membrane system with separation of laps/seams likely in the roof membrane and/or separation of flashing membranes from the roof membrane sheet. Either condition will allow water to pass into the lap/seam area. With water comes contaminants—dirt, feathers, gravel, sand, weeds, seeds, etc., which will accumulate on sticky surfaces of the self-adhered membranes and make repairs to open lap/seam areas a challenge. It may be necessary to apply an external heat source to critical lap areas at the time of installation to ensure positive bonding of self-adhered materials.

Self-adhered seam tapes, batten bar tapes and perimeter reinforcing strips commonly incorporated into thermoset (EPDM) roof membrane systems have been successful thanks to a variety of cleaners and primers applied to membrane surfaces before bonding the self-adhered materials. The use of similar cleaners and primers may be necessary with some self-adhered roof membrane systems to ensure positive bonding of joints and junctures. If solvent-based cleaners and primers become necessary to ensure satisfactory performance of self-adhered roof membrane systems, some attractive qualities of self-adhered roof membrane systems disappear. Additional material and labor costs, as well as volatile organic compound (VOC) regulations, may negatively affect the acceptance of self-adhered roof membrane systems.

In addition, self-adhered roof membranes may be essentially unusable in cold temperatures. The sheets will become stiff and unyielding in temperatures below 50 F (10 C), and the self-adhered backer will have insufficient immediate adhesion properties to resist the curl of the self-adhered sheets under thermal contraction. It would not be practical (or economical) to apply supplemental heat to the complete self-adhered membrane to ensure adhesion to the substrate. Rolling the sheet may help but would provide no assurance of reasonable adhesion.

Substrates

Self-adhered roof membranes will not bond (or remain bonded) to just any substrate. Substrates for self-adhered roof membrane applications are not created equally. Fiberglass facers should be the rule for polyisocyanurate foam roof insulation substrates to minimize the moisture-absorption properties of paper-faced polyisocyanurate foam roof insulation. A sealed surface, such as Dens Deck Prime, should be the rule for moisture-resistant gypsum substrates or Denver-based Johns Manville's DuroBoard perlite-based roof insulation.

Typical wood fiber roof insulation with an asphalt-saturated surface (assuming the material is dry) should suffice for a cover board in roof areas with heavy foot traffic. Installation over damp wood panels (oriented strand board or plywood) probably will result in disbonding of the self-adhered membrane after a short time (assuming it sticks initially).

Substrates for proper installation must be free of dust and debris and any moisture that might inhibit bonding of the self-adhered membrane to substrate surfaces.

Needless to say, self-adhered roof membrane systems will not remain bonded to wetted roof insulation or wet roof insulation facers.

It will be just as critical to replace wet or moisture-damaged roof insulation under self-adhered roof membrane systems as it would be under any other roof membrane system.

Other issues

Some interesting combinations of traditional and self-adhered materials have become available. New EPDM roof systems that incorporate inherent self-adhered tapes for bonding a membrane to a substrate are being offered by at least one manufacturer. The same caveats that apply to composite roof systems apply to self-adhered synthetic sheet roof systems; selection of substrates will be limited, and the same ambient-weather conditions that affect other self-adhered roof membranes will affect composite systems.

The size of self-adhered polymeric roof membrane rolls may be limited by weight because the self-adhered backer and parting sheet weigh at least as much as the polymeric sheet itself. Rolls heavier than 200 pounds (90.7 kg) would be unwieldy in the field; difficult to place and align; and difficult to correct should alignment become errant, such as over tapered roof insulation systems. TPO roof membranes are stiff and boardy—enough so "memory" of the TPO sheet may overcome the adhesive bond, resulting in voids beneath the roof membrane, especially at transition areas or changes in plane. Smaller rolls definitely will have an advantage in the application process.

Accessories with self-adhering base materials are available from various suppliers. Vent pipe closures, pitch pans and drain inserts are among the accessory items available with a self-adhered material pre-applied to the flanges.

A degree of caution is in order when using these accessories with any roof membrane type. Roof membrane surfaces must be thoroughly cleaned of contaminants, including mineral-granule surfacing materials, before installating accessory units. Remember, if no stripping membrane is installed over the metal flanges, an absolutely positive seal is required at the penetration flashing to prevent costly callbacks and unhappy customers. And some self-adhered components may remain "stuck" longer than others.

Potential problems

Application recommendations may vary from supplier to supplier, but all self-adhered roof membranes have some common potential problem areas. The necessity for special attention at T-laps and offsetting end laps are common to bituminous and polymeric self-adhered roof membranes.

Positively sealing T-laps will be much easier on polymeric self-adhered roof membranes than on bituminous self-adhered roof membranes. Patches of nonreinforced polymeric membrane material can be heat-welded or adhered over T-laps to seal them against water entry from the roof membrane's surface.

Sealing T-laps on a mineral-surfaced polymer-modified asphalt roof membrane may be much more challenging and painful. The use of surface patches on T-laps on mineral-surfaced cap sheets will be unsightly at best and just plain ugly at not-so-best. Mineral granules must be embedded in the area of the patch to ensure a bitumen-to-bitumen bond. Cutting off the corners of the bottom sheet in the lap of a polymer-modified asphalt roof membrane system on a 45-degree angle will help, but some serious physical embedment of the top layer of the cap sheet will be in order along with some heat. Additional bituminous sealants may be necessary in the overlap area to positively seal the juncture area.

All self-adhered roof membranes will want to bridge over the change in plane created by a T-lap whether a membrane is bituminous or polymeric; there is no escaping the abrupt change in plane at the overlapped area.

Offsetting end laps in self-adhered roof membrane sheets will be more critical than offsetting sheet ends in hot- or adhesive-applied roof membrane systems simply because there is no fill material on the sticky side of a self-adhered sheet. End laps that are coincident with adjacent sheets or in proximity to end laps in adjacent sheets may be difficult to seal simply because of the material's mass and proximity of the plane changes. Application by butting the ends of rolls and applying a cover sheet over the juncture will result in numerous T-laps along the longitudinal sides of the strapped sheet, which must be addressed individually.

Maintaining roll alignment during installation will be critical to expedite installation of self-adhered sheets. Installation by the "scroll" method commonly used in the application of torch-applied polymer-modified asphalt sheets may help ensure initial alignment. In most circumstances, one doesn't get a second chance to adjust a roll's alignment when installing a self-adhered sheet. It may be necessary to cut the sheet at changes in plane or transition areas to maintain a satisfactory side lap and/or cover the selvage edge of mineral-surfaced cap sheets. Self-adhered sheets will not conform to tapered insulation drain sumps, and the use of targets at recessed drains will be necessary.

Constructing flashings with a self-adhered membrane will be a challenge with heavy or boardy self-adhered sheets. Good surface preparation will be essential, and areas of the lap between sheets should be cleaned thoroughly (and perhaps primed) before attempting to mate self-adhered sheets at overlaps. It is not likely self-adhered polymer-modified bituminous membranes installed as flashings will bond effectively to mineral-granule-surfaced roof membranes. Embedding of surfacing granules will be necessary to allow an adhesive-to-bitumen bond at the lapped area. Mechanical attachment of self-adhered membrane flashings will be every bit as critical as with conventional membrane flashing construction. Corners may be a challenge to construct depending on the material being installed, and most will require "stripping" to ensure a positive seal at joined areas.

"Creep" is associated with plastic-type materials that move under the influence of gravity to low areas. Self-adhered asphalt-based roof membranes (depending on the composition of the self-adhered material on polymeric roof membranes) may be subject to creep. The most positive way to minimize the effects of creep is to ensure self-adhered roof membranes installed on steep slopes get a little help from mechanical attachment to the substrate. Strapping, or running roof membrane rolls parallel to the roof slope, will minimize the potential for creep with minimal mechanical attachment at the top end of the roll.

Some advice

There will be a lot of waste with self-adhered roof membrane systems. Parting sheets will rapidly accumulate, and a method of containing and disposing of parting sheets should be considered.

Surface preparation and substrate selection will be critical to the performance of self-adhered roof membrane systems. Attempting to assemble self-adhered roof membrane systems with unsuitable substrates will cause early system failure. The use of cleaners and primers, as well as supplemental sealants, may be necessary to successfully complete a self-adhered roof membrane system. Manufacturer's recommendations for installation should be followed, but remember, many suppliers have less experience than some contractors in the installation of their new systems and materials.

Self-adhered roof membrane systems offer some nice advantages in some situations, but caution must be exercised. Initial installations and details will require considerable attention to ensure satisfactory installations.

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