vapor retarder for projects in the SOUTHNAVFACENGCOM
area.
Vapor retarder may be specified for heated buildings
where the average January temperature is below 5
degrees C (40 degrees F) and the expected interior
winter humidity exceeds 45 percent. Vapor retarder
will be specified for heated buildings where a high
humidity condition is expected, such as indoor
swimming pool or laundry.
Where a vapor retarder is to be installed, the
that the dew point is on the cold side of the vapor
methods in agreement with ASHRAE Handbook,
Fundamentals.
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Install vapor retarder in direct contact with [roof deck surface]
[ventilating felt] [insulation]. Vapor retarder shall consist of [either]
two plies of No. 15 asphalt-saturated felt, two plies of asphalt-coated
glass felt [, or one layer of asphalt-saturated felt base sheet]. Lay
vapor retarder at right angles to direction of slope. Install first ply of
felt [or base sheet] as specified herein for the specific deck. Apply
second ply of 2-ply vapor retarder system using asphalt at rate of 10 to 18
kgs per 10 square meters 20 to 35 lbs per 100 square feet, applied within
plus or minus 15 degrees C25 degrees F of EVT. Do not heat asphalt above
asphalt's FBT or 275 degrees C 525 degrees F, whichever is less. Use
thermometers to check temperatures during heating and application. Side and
end laps shall be completely sealed. Asphalt shall be visible beyond all
edges of each ply as it is being installed. Plies shall be laid free of
wrinkles, buckles, creases or fishmouths. Workers shall not walk on mopped
surfaces when the asphalt is sticky. Press out air bubbles to obtain
complete adhesion between surfaces. At walls, eaves and rakes, and other
vertical surfaces, the vapor retarder organic felts shall be extended 225
mm, 9 inches, or separate organic felt plies shall be extended 225 mm, 9
inches, with not less than 225 mm 9 inches on the substrate, and the
extended portion turned back and mopped in over the top of the insulation.
At roof penetrations other than walls, eaves and rakes, and vertical
surfaces, the vapor retarder or separate plies shall be extended 225 mm 9
inches to form a lap which shall later be folded back over the edge of the
insulation. Asphalt roof cement shall be used under the vapor retarder for
at least 225 mm 9 inches from walls, eaves, rakes and other penetrations.
[3.2.1
Vapor Retarder on Poured Concrete Decks
Solidly mop primed substrate with asphalt at rate of 10 to 18 kgs per 10
square meters 20 to 35 lbs per 100 square feet before installing vapor
retarder. Lay first ply of 2 ply system with each sheet lapping 480 mm 19
inches over the preceding sheet. Lap ends not less than 100 mm 4 inches.
Stagger laps a minimum of 300 mm 12 inches. [For a vapor retarder
consisting of one layer of asphalt base sheet, provide side and end laps
not less than 100 mm 4 inches. Stagger laps a minimum of 300 mm 12 inches.
Cement base sheets together with a solid mopping of asphalt.]
][3.2.2
Vapor Retarder on Precast Concrete Decks
Solidly mop primed substrate with asphalt at rate of 10 to 18 kgs per
SECTION 07220
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