Glossary – Dow Protected Membrane Roof EN User Manual

Page 5

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Glossary

Humidity:

the amount of

moisture contained in the
atmosphere. Generally expressed
as percent relative humidity
(% RH). It is the ratio of the
amount of water vapour actually
present in the air, compared to
the maximum amount that the
air could contain at the same
temperature.

Inverted Roof Membrane
Assembly (IRMA):

same as

protected membrane roof (PMR)
assembly, where a closed-cell
insulation (e.g., STYROFOAM

™

Brand XPS Foam Insulation) and
ballast are placed over the roof
membrane.

Live Load:

temporary load

that the roof structure must be
designed to support, as required
by governing building codes.
Can include people, installation
equipment, vehicles, wind,
snow, ice or rain, etc.

Loose-laid Membrane:

mem-

brane that is not attached to the
substrate except at the perimeter
of the roof and at penetrations.
Typically, a loose-laid membrane
is held in place with ballast.

Mechanically Fastened
Membrane:

membrane that is

attached at defined intervals to
the substrate, using various fas-
teners and/or other mechanical
devices.

Membrane:

a flexible or

semi-flexible material that water-
proofs (excludes water) a roof.

Parapet Wall:

that part of a

perimeter wall immediately
adjacent to the roof, which
extends above the roof.

PMR:

protected membrane roof.

Positive Drainage:

the drainage

profile of a deck, considering
the roof slope and loading
deflections to ensure the roof
deck drains within 48 hours of
rainfall during ambient drying
conditions.

Ridge:

highest point on the roof

where two roof areas intersect.

Roof Assembly:

an assembly

of interacting roof components
(includes the roof deck, vapour
retarder [if present], insulation
and roof covering).

Roof Slope:

the angle a roof

surface makes with the horizon-
tal. Typically expressed as a ratio
of rise to run, such as 4:12, or as
a percent.

Square:

100 ft

(9.29 m

) of roof

area.

Substrate:

the surface on which

the roofing or waterproofing
membrane is applied (e.g., the
structural deck or insulation).

Vapour Retarder:

a material

that restricts the movement of
water vapour.

Wind Uplift:

the force caused by

the deflection of wind at roof
edges, roof peaks or obstructions,
causing a drop in air pressure
immediately above the roof
surface (e.g., suction). Uplift may
also occur from air movement
from underneath the roof deck,
causing the membrane to balloon
and pull away from the deck.