Gaps, Flashings, Joints, and Sealants.

CEMP-ET

TI 809-53

01 May 1999

(b) Flood coat and gravel. Quantities, materials, and techniques are identical to BUR.

Flood coats and gravel are usually used only in ponded water situations or where a more robust

surface is needed for hail protection.

(c) Field applied color coatings. Asphalt aluminum coatings (ASTM D2824) and white

latex coatings (ASTM D6083) are used for heat reduction and UV protection. These will require

periodic recoating.

l. Penetrations and Flashings. MB systems are well suited as flashings. They are compatible

with and used on both BUR and MB roof systems.

m. Historical Roof Restoration. The many surfacing options of MB allow the finished appearance

to match the designer's choice. Copper foil surfacing gives an appearance of copper roofing and has

been used in domed structures as a low cost simulation of sheet copper.

n. Aesthetics. Mineral surfaced sheets, when installed neatly, can have a reasonably pleasing

appearance. Loose granules may be sprinkled into exposed bitumen at end and sidelaps to improve

aesthetics. The exposed bitumen on foil surfaced sheets may be touched-up with special paint

provided by the MB sheet producer. Gravel surfaced roofs appear identical to BUR. Coated systems

will be pleasing for a while, but recoating will be needed to maintain the appearance.

o. Gaps, Flashings, Joints, and Sealants.

(1) Gaps. Gaps in insulation in excess of 6 mm (1/4 in.) should be filled with thermal

insulation by inserting pieces of insulation or replacing broken boards. Gaps in nailable decks are

bridged with sheets of galvanized steel.

(2) Flashings.

(a) Vertical flashings for most MB systems require cant strips to reduce the angle at the

base of the wall or curb. NRCA details, on occasion modified to specific job conditions, should be

followed.

(b) Base flashings should extend not less than 200 mm (8 in.) above the membrane.

(c) Metals should not be used as base flashing but are suitable as counterflashing

materials.

(d) Metal gravel stops embedded in the roof membrane should be avoided wherever

possible, as they require frequent maintenance. When used they must be attached securely

(3) Sealants. Sealants are used primarily for metal work. Asphalt mastics (ASTM D2822 or

D4479) are used on bituminous flashing details. Occasionally melted MB coating is scraped from the

back side of scrap MB sheeting and used as a hot melt sealant.

p. Drainage, Valley and Intersection Details.

(1) Drainage. Roof drains should be sized to meet national plumbing codes. Secondary

(overflow) drains or scuppers should be designed in accordance with ANSI/ASCE 7-95. Over-the-

eaves drainage is acceptable in areas where ice dams are not expected. Interior drains avoid drain

and leader freeze-up. Primary roof drains should be recessed below the roof line by using deck sumps

(uninsulated decks) or by creating a sump out of roof insulation in order to properly collect water.

(2) Valley and Intersection Details. Valleys and intersections are fabricated out of membrane

materials. Crickets and saddles help divert water to the drains. Refer to NRCA details for their design.

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