and
Leak Barrier
UnderRoof™ HT and UnderRoof™ 2 Leak Barrier
Application Instructions for
Use as a Vapor Retarder in Low-Slope Membrane Roof Systems
A number of basic considerations factor into the need for and location of a vapor retarder. Determining the need for and
location of the vapor retarder is the responsibility of the Design Professional. See GAF roof system application manuals for
additional water vapor transfer information and additional vapor retarder application information. Note: Vapor retarders are
not considered part of a GAF roofing system and are not included in any GAF roof guarantee.
Acceptable Substrates:
•M
inimum 48” x 48” x ½” (1.22 m x 1.22 m x
12.7 mm) USG SECUROCK® Roof Board mechanically
fastened to the deck.
• Minimum 48” x 48” x 5/8” (1.22 m X 1.22 m x
15.9 mm) DensDeck® DuraGuard Roof Board
mechanically fastened to the deck.
• Dry, cured, primed structural concrete. Structural
concrete must be primed with ASTM D41 primer.
Acceptable Insulation & Attachment to
UnderRoof™ HT and UnderRoof™ 2 Leak
Barrier:
•E
nergyGuard™ Polyiso Insulation [max. 48” x 48”
(1.22 m x 1.22 m)] adhered with OlyBond® 500 or
OlyBond® 500 Green applied in ¾” – 1” (19.1 – 25.4
mm) wide ribbons spaced 12” (305 mm) o.c. (see below
for minimum thickness and optional coverboards)
Factory Mutual Research
Corporation Approvals
New/Tear Off Combinations &
Wind Ratings Summary:
—Steel Deck with UnderRoof™ 2 and
UnderRoof™ HT: Meets Class 1-90
—Primed Structural Concrete Deck with
UnderRoof™ HT: Meets Class 1-75
­—P
rimed Structural Concrete Deck with
UnderRoof™ 2: Meets Class 1-255 depending on roof
cover and substrate chosen (contact Technical Services or
see roofnav.fmglobal.com for specifics)
• Min. 22 ga. Steel Deck | min. 48” x 48” x ½”
SECUROCK® Gypsum-Fiber or min. 48” x 48” x 5/8”
DensDeck® DuraGuard thermal barrier mech. attached
within a contributory area of 2.67 ft2 per fastener
(6 fasteners per 4’ x 4’ board or 12 fasteners per
4’ x 8’ board) | UnderRoof™ 2 or UnderRoof™ HT vapor
retarder self-adhered and rolled with a weighted roller |
Min 1.5” thick EnergyGuard™ RH, RM, RN Polyiso (max
48” x 48”) adhered with OlyBond® 500 or OlyBond® 500
Green applied in ¾” - 1” wide ribbons spaced 12” o.c.
| OPTIONAL min. 48” x 96” x ¼” gypsum cover board
adhered with OlyBond® 500 or OlyBond® 500 Green
applied in ¾” - 1” wide ribbons spaced 12” o.c. | A roof
cover below approved with the substrate is installed (see
below for approved roof cover and substrate combinations)
• Primed Structural Concrete Deck | UnderRoof™ 2 or
UnderRoof™ HT vapor retarder self-adhered and rolled
with a weighted roller | Min 0.5” thick EnergyGuard™
RH, RN Polyiso (max. 48” x 48”) or min. 1.5” thick
EnergyGuard™ RM Polyiso (max. 48” x 48”) adhered
with OlyBond® 500 or OlyBond® 500 Green applied
in ¾” - 1” wide ribbons spaced 12”. o.c. | OPTIONAL
min. 48” x 96” x ¼” gypsum cover board adhered with
OlyBond® 500 or OlyBond® 500 Green applied in ¾” 1” wide ribbons spaced 12” o.c. | A roof cover below
approved with the substrate is installed (see below for
approved roof cover and substrate combinations)
Roof Covers & Substrates:
• L iberty™ SBS Self-Adhering Base/Ply Sheet, Ruberoid®
SA Base/Ply Sheet, WeatherWatch® XT self-adhered
+ Ruberoid® Torch or SBS-Heat Weld Cap over
DensDeck® DuraGuard, SECUROCK® Gypsum-Fiber, or
EnergyGuard™ RH, RM, RN Polyiso
• Ruberoid® SA Cap FR + Ruberoid® SA Base/Ply Sheet
self-adhered and rolled with a weighted roller over
Dens Deck® DuraGuard, SECUROCK® Gypsum-Fiber, or
EnergyGuard™ RH, RM, RN Polyiso
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•E
verGuard® TPO (smooth) fully adhered with
EverGuard® WB 181, EverGuard® TPO #1121, or
EverGuard® Low VOC TPO Bonding Adhesive over
DensDeck® Prime, SECUROCK® Gypsum-Fiber, or
EnergyGuard™ RH, RM, RN Polyiso
• EverGuard® TPO FB Ultra fully adhered with
EverGuard® WB 181 Bonding Adhesive over DensDeck®
Prime, SECUROCK® Gypsum-Fiber, or EnergyGuard™
RH, RM, RN Polyiso
• EverGuard® TPO FB Ultra adhered with LRF Adhesive
O applied in ¾” - 1” wide ribbons spaced 12”. o.c.
over DensDeck® Prime, SECUROCK® Gypsum-Fiber, or
EnergyGuard™ RH, RM, RN Polyiso
• EverGuard® Freedom™ TPO HW or EverGuard®
Freedom™ TPO with RapidSeam™ Technology
self-adhered over DensDeck® DuraGuard, SECUROCK®
Gypsum-Fiber, or EnergyGuard™ RM, RN Polyiso
What to do before you begin…
1. C
heck the temperature… install only when the
outside temperature is 45ºF (7ºC) and rising. In cool
weather membrane rolls and adhesives must be stored
overnight at a minimum temperature of 55°F (12.8°C)
prior to their application. Remove all rolls from the
heated storage only as they are being installed. Install
membrane rolls immediately after removal from storage
to avoid membrane cooling. Leak barrier rolls must be
at least 45°F (7.2°C) at time of application.
2. Examine the deck or substrate… make sure the surface
is clean, dry, and free of sharp edges. Any ice, dew,
water, debris, dirt, oil, grease, or other contaminates
will interfere with adhesion and may lead to a leak.
3. Examine the substrate for defects… repair where
necessary.
4. Leave the release liner in place… until you are ready
to adhere the vapor retarder to the deck or substrate.
5. Do not use UnderRoof™ HT or UnderRoof™ 2 Leak
Barrier self-adhering vapor retarders as a temporary
roof… in commercial/low-slope applications.
6. Safety note… any time installation takes you near the
edge of the roof, use special safety precautions. Refer
to your company safety manual for guidelines.
Field Sheet Installation… First Course
1. S
tart at the low point or drains… so the flow of water
is over or parallel to the laps, but never against the
laps. To aid in handling and sheet alignment and to
minimize wrinkling, the membrane may be cut into a
workable length [approximately 10’ - 20’ (3 - 6 m)].
Install the sheets perpendicular to the slope. Fold the
membrane over lengthwise and remove the release liner
from half the sheet and roll in the sheet.
2. Proceed to the other half… of the first sheet. Fold over
the other half of the sheet lengthwise. Use care to keep
the sheet straight.
3. Peel the release film… from this half of the sheet. It
peels easiest when pulled at a 45º angle along the
length of the sheet. Avoid touching the adhesive as you
remove the film, as it is very aggressive.
4. Roll in this half of the membrane… keeping the sheet
rounded as it adheres to the substrate. Once the entire
sheet is installed, roll the sheet with a weighted roller to
assure proper adhesion.
5. Work carefully… if the membrane runs off of the
proper alignment by more than ¼” (6 mm), cut and
restart the membrane installation.
Field Sheet Installation… End Laps
­—For UnderRoof™ HT Leak Barrier end laps:
1. Align the new sheet… so that it overlaps the previous
sheet 6” (152 mm).
2. After removing the release film… firmly roll the end
lap with a silicone-coated hand roller to ensure sealing.
—For UnderRoof™ 2 Leak Barrier end laps:
1. Align the new sheet… so that it overlaps the previous
sheet 6” (152 mm).
2. A
t the overlap… fold the sheet back to a point 12”
(304 mm) from the end of the roll.
3. S
core the release liner… leaving the 12” (304 mm)
section in place. Be sure to score the release liner of the
selvedge edge at the same point.
4. Install the balance… of the membrane as you normally
would.
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5. R
eturn to the end lap area… and fold back that
portion of the membrane where the release liner is still
in place.
6. A
pply TOPCOAT® Matrix™ MajorBond™ Flashing
Cement or TOPCOAT® Matrix™ Premium 201 SBS
Flashing Cement… in the 6” (152 mm) area of the
bottom sheet forming the end lap. Trowel to an
even thickness approximately 1/16” (2 mm) to
1
/8” (3 mm) thick.
7. T o complete the end lap… remove the release film from
the back of the top sheet, the 12” (304 mm) piece left
in place in previous step. Set the top sheet into adhesive
and firmly roll the sheet with a silicone-coated roller to
ensure sealing.
Field Sheet Installation… Subsequent Courses
1. P
osition subsequent courses… using the selvedge edge
line to align the membrane.
—UnderRoof™ HT Leak Barrier requires a minimum
3” (72 mm) side lap.
—UnderRoof™ 2 Leak Barrier requires a minimum
4” (102 mm) side lap.
2. B
e sure… to firmly roll the lap area with a siliconecoated hand roller at the end to ensure sealing.
Seal all roof edges and penetrations
•A
ll roof edges and penetrations must be sealed to
retard moisture vapor migration at these locations.
If UnderRoof™ HT or UnderRoof™ 2 Leak Barrier is to
be adhered to concrete or metal surfaces, the surfaces
must be primed with ASTM D41 primer and allowed to
dry. Firmly roll the sheet with a silicone-coated roller to
ensure adhesion.
Precautionary Note: The application of this product
or the roof system may require the use of adhesives or
cements that contain solvents. Apply these adhesives/
cements ONLY as instructed. Application of excess
solvent-based adhesives or cements may affect the
performance of this product, resulting in the asphalt
flowing, dripping, and staining.
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