Tips on Installing Self Adhering Roof Membrane for Flat or Low Slope Roofs
Low slope areas such as car ports, garages, porches and sun rooms - anything below a 2 / 12 pitch requires special attention. Without the drainage of a steep slope, these roofs can take a hard beating from rain, ice and snow. You've probably seen the problem leaks that occur where these low sloped roofs tie in with the main house. To provide you with materials that can meet these challenges GAF has developed a series of self-adhering membranes that go down easy, apply with simple tools, and provide maximum protection. Let's take a look at these revolutionary low slope products and see how they install.
Liberty is a system for low slopes, with a pitch between 1/2 inch to 6 inches per foot. Designed as a complete roofing system, these membranes serve as a waterproofing for the field of the roof and also are applied as flashings at parapets, perimeter terminations, and typical rooftop penetrations. The Liberty product line consists of three membranes.
- The Liberty cap sheen and two base sheets
- Liberty mechanically attached base sheath
- Liberty self adhering base ply sheet
Incorporating all three membranes helps assure a premium membrane assembly. Self adhering base sheets may be applied directly to wood decks. However, from a long-term perspective that option limits re-roofing potential. The best option for long-term performance includes the premium Liberty 3 ply system. Liberty mechanically attached base sheet first. Liberty self adhered base sheet next. And the Liberty cap sheet on top. To ensure proper adhesion of any Liberty self adhered system, it must be installed when the weather is dry and forty-five degrees Fahrenheit or higher.
The substrate for the Liberty system must be clean and dry. All penetration curbs, perimeter cants, nailers etc, must be in place.
We will now look at the installation of a Liberty system installed over an uninsulated wood deck. Liberty mechanically attached base sheet, also called Liberty MA base, is a one metre (or 39 3/8 inch) wide membrane that is surfaced on the top with a plastic film designed to maximize the attachment of other self adhering Liberty membranes. This sheet is designed to be mechanically attached directly to the deck, or installed above board insulation. For installation over board insulation, see the Liberty instructions.
Over nailable decks, the Liberty MA base sheet is nailed with a typical base sheet pattern, using one inch square or round metal capped nails. Start by cutting the Liberty MA base sheet into one-third width strips to ensure that the cap sheets side seams do not line up directly over the base sheet seams. Starting at the low side of the roof, position the one-third with sheet parallel to the edge of the roof. Overhang the roofs edge to accommodate the anticipated perimeter termination detail. Allow the sheet to relax and remove any wrinkles to provide the smoothest surface for other plys.
Whether installing Liberty mechanically attached base sheet, or Liberty self adhered base sheet, your edge metal details are the same. At the edge of the roof, install drip edges. Primed metal drip edge is required at eaves and rakes on Liberty systems. At eaves and rakes, install the bed of topcoat matrix 201 premium SBS flashing cement to set the metal drip edge into. Next, to better seal the flange at the base sheet base ply, nail the drip edge three inches on center in a staggered pattern using roofing nails.
Finally, apply a 1/16 to 1/8 inch troweling of matrix 201 premium SBS flashing cement to the top of the metal, prior to installing the Liberty cap sheet over drip edges. Using a notched trowel helps assure a proper application rate of adhesive. Liberty systems require the use of SBS adhesives and cements. Other non SBS cements may have an adverse reaction, and damage the Liberty membrane.
Where flanged metal termination and penetration flashings are to be installed, they must be primed and should be installed in a 1/8 to 1/16 inch troweling of matrix 201 premium SBS flashing cement over the Liberty base ply sheet. In addition, apply a troweling of matrix 201 premium SBS flashing cement to the top of any metal flanges prior to the application of the Liberty cap sheet.
Now install the remaining base sheets. The first row of fasteners at the edge of the roof will be one to two inches from the leading edge and on nine inch centers. Subsequent courses of mechanically attached base sheet are positioned with the side lap aligned to the ley line on the preceding sheet. Position the sheet and avoid wrinkles. Allow the sheet to relax. Locate fasteners in the lap formed with the next course of base MA.
Next, locate the second row of fasteners 14 inches from the leading edge on 18-inch centers. The third row of fasteners should be 26 inches from the leading edge on 18-inch centers. The centers for the second and third rows should be staggered to minimize the risk of uplift and other movements.
Continue to apply base sheet MA across the roof overlapping the end of the preceding sheet a minimum of 6 inches. Where wind uplift resistance is a concern, you may apply a bead of caulk in this overlap, and then nail the overlap area a minimum of 6 inches on center. End laps and adjacent courses should be offset a minimum of 36 inches to reduce the risk of leaks.
The Liberty self and hearing base ply sheet is also a 1 meter (or 39 and 3/8 inch) wide membrane that has a plastic film top surface designed to receive the Liberty cap sheet. On the bottom, the surface is a splint back release film designed to be removed to uncover a self adhering surface. The Liberty self adhering membranes have extremely aggressive self adhering properties. When installed directly to wood, they will adhere very strongly. While the adhesion to wood is good without primer, the best long-term adhesion is achieved when the wood is lightly primed with one coat of matrix 307 asphalt concrete primer, or a comparable ASTM D41 type primer.
Remember to allow the primer to dry completely prior to the installation of the Liberty self adhering base sheet. Over application of primer, or application of the membrane over wet primer, may cause the roof to blister. Cut a two-thirds width of the Liberty base ply and align it with the edge of the roof, plus whatever is required to turn down on the fascia.
Position the selvage line on the high side of the roof to provide an overlap guideline and to assure that water flows over the side. Next fold the sheet away from the edge of the roof along its length, exposing the bottom of the sheet. Remove the narrow width of release film from the back of the sheet. Working from the center of the length of the Liberty base ply, allow the sheet to roll on to the deck, being careful to avoid wrinkles and trapped air and while maintaining proper alignment with the edge of the roof. The resulting smooth surface assures a sound, receptive substrate for the Liberty cap sheet.
Firmly press the sheet to avoid wrinkles and craft air as the ply adheres to the deck, and press down the fascia. Position the selvage line on the high side of the roof to provide an overlap guideline, and to assure that water flows over the side laps. Now fold the top portion of the sheet back on itself exposing the remaining release film. Remove the release film, and then roll the sheet into place working from the center of the sheet outward, towards the ends of the sheet. Firmly hand press the sheet to avoid wrinkles and trapped air. Where additional lengths of Liberty base ply are added in the same course, overlap the end of the previous sheet a minimum of six inches to provide the best protection against leaks.
On the upper, overlapping sheet cut the selvage edge at a 45 degree angle to provide a tapered transition at the t-joints formed by succeeding courses. This provides a smooth transition and reduces the chance for blisters and loose laps. End laps and adjacent courses should be offset a minimum of 36 inches. Install additional courses of Liberty base ply as follows:
- Align the base ply with the installation line on the sheet in the previous course.
- Fold the sheet in half, away from the selvage edge of the lower sheet along its length exposing approximately half of the bottom of the sheet.
- Remove the exposed release film.
- Working from the center of the length of base ply sheet, allow the sheet to roll onto the primed deck, being careful to avoid wrinkles and trapped air while maintaining proper alignment with the selvage edge of the previous course.
- Firmly hand press the sheet to avoid wrinkles and trapped air. Fold the other half of the sheet back on itself exposing the remaining release film.
- Remove the release film, and roll the sheet in place working from the center of the sheet outward toward the ends of the sheet.
- Complete any side lap installations by hand pressing and rolling the lap.
- Apply uniform pressure to the entire area by using a method suitable to the roof slope. A long-handled push broom or a weighted roller is ideal. This creates a solid bond between plies.
The next step is the installation of the cap sheet. Roll out and cut manageable lengths of Liberty cap sheet. Before installing, let the sheets relax on the roof. This allows the ends of the rolls to lay flat, giving a much better finished roof. At the low point on the roof, align a length that allows a wrinkle-free installation of a full width sheet of Liberty cap sheet. The selvage edge of the sheet should be positioned up the roof. Fold the sheet away from the edge of the roof along its length, exposing approximately half of the bottom of the sheet. Remove the release film from the sheet. Working from the center of the length of cap sheet, allow the sheet to roll onto the base ply sheet. Firmly hand press the sheet to avoid wrinkles and trap air. Now fold the other half of the sheet back on itself, remove the release film and roll the sheet in place, working from the middle to the outside edges.
Applying a bead of matrix 201 premium SBS flashing cement adhesive along the top edge of each cap sheet, and at any selvage edge t-joints in any self adhered system, minimizes the possibility of lap blisters forming, and seals one row from another. Firmly press or roll the sheet to avoid wrinkles and trapped air in the cap sheet.
Due to the thickness of Liberty cap sheet, this weight can pull the membrane down-slope. Overlap the end of the previous sheet by a minimum of six inches. It is a good idea to leave a minimum eight inches of release film on the back of the overlapping cap sheet. This will prevent unwanted bonding to the granule surface of the underlying sheet when installing the adjoining sheet. End laps and adjacent courses must be offset from one another by at least 36 inches.
On the upper sheet cut the selvage edge at a 45 degree angle to provide a smooth, tapered transition at the t-joints formed by succeeding courses. Complete the overlapping end joint by pulling the overlapping edge back, and applying matrix 201 premium SBS flashing cement to the granule surface of the underlying sheet, using a notched trowel. Spread the cement to a thickness of approximately 1/16 to 1/8 of an inch. At the selvage edge remove only enough release film to accommodate the end lap. To ensure a good end lap, roll the lap area after installation. Install additional courses of Liberty cap sheet as follows:
- Position the cap sheet to overlap the previous courses selvage edge width.
- Fold the sheet in half away from the selvage edge of the lower sheet along its length, exposing approximately 20 inches, or 508 millimetres, of the bottom of the sheet.
- Remove the selvage edge release film from the underlying sheet, except for the short piece in any overlap section of end laps.
- To ensure a good end lap, role the lap area after the installation.
- To complete the application of the cap sheet, roll the entire membrane with a weighted roller to assist with adhesion. Any adhesive bleed out can be covered with loose granules present a more professional and pleasing appearance.
Flashing of walls roof terminations and penetrations can also be done with Liberty membranes and pre flashed SBS and weld units. As with all vertical flashings, the flashing is nailed off at the top and counter flashed.
Liberty is just one of the self adhered products offered by GAF. Others include the freedom series of self adhered TPO roofing membranes. Freedom membrane is a tough, commercial grade membrane that is easy to install ,long lasting and energy efficient with a white reflective surface.