01 May 1999
better to separate the cooler or freezer from the roof system by at least a 600 mm (2 ft) air space. The
vapor retarder for the cooler or freezer is then positioned on the exterior of the freezer box facing the
Thermal Insulation and Heat Flow.
(1) Polyisocyanurate Insulation.
Isoboards are heat resistant.
membranes should not be mopped directly to them. A layer of non-foam insulation should overlay the
isoboard foam. Typically wood fiber or perlite board is mopped to the isoboard and the BUR is mopped
(2) Re-cover Boards. Perlite, glass fiber, and wood fiber are used in re-cover situations
where increasing thermal insulation is not a primary objective.
(3) Thermoplastic Foams. Polystyrene foam is damaged by hot asphalt. Some attempts have
been made to adhere EPS with hot bitumen by allowing some cooling prior to embedment of the
polystyrene. This technique is very vulnerable to workmanship error: too cool--no adhesion; too hot--
insulation damage. The aliphatic and aromatic solvents used in cold process BUR adhesives also
Membranes and Surfacings.
(1) Reinforcements. Base sheets, ply felts, and mineral surfaced capsheets are used. Glass
fiber mats dominate the market with small percentages of organic and synthetic fiber materials used.
(Asbestos felts were used in the recent past.)
(a) Base sheets are used in nailable specifications. They generally have heavier asphalt
coating for water and puncture resistance. Special base sheets have granules and channels on the
bottom side to allow lateral movement of vapor.
(b) Ply sheets are thin, porous, conformable materials designed to lie securely into
mopping bitumen. Asphalt treated felts are used with asphalt while tar treated materials are used with
coal tar pitch moppings.
(c) Heavier coated ply sheets are generally used with cold applied bituminous adhesives.
The heavier coating reduces demand for waterproofing bitumen from the adhesive and also permits
light foot traffic during application without excessive bleed through. They may not be as heavy as
(d) Mineral surfaced capsheets provide a lightweight reflective surfacing. They are
especially popular in Arizona, California and Hawaii where aggregate surfaced roofs are less
(2) Bitumen. Asphalt is available in four mopping grades as described in ASTM D312. Type
III is generally selected with glass fiber membranes, with Type IV used in the hot desert. Type I is
sometimes used as a flood coat on roofs with a slope to 2% (1/4 in./ft.) because of superior water
resistance. Coat tar pitch is available in two roofing grades as described in ASTM D450. Type I is
called old style pitch and Type III is called low fuming. Both grades are suitable for slopes below 2%
only. Suppliers are currently recommending Type I pitch only.
(a) A flood coat of bitumen is poured on the roof surface at a rate of approximately 2.9
kg/m (0.60 psf), followed by aggregate meeting ASTM D1863 at a rate of 19-24 kg/m2 (4-5 psf).