Fahrenheit (F) (66 degrees C) can be reached. Temperature ranges
of more than 100 degrees F (38 degrees C) can be experienced in a
Moisture. Provisions for expansion and contraction of
roof insulation due to changes in moisture content should be made
in the same manner as for temperature changes. Depending upon
the type of insulation material utilized, the change in dimension
due to moisture can exceed that due to temperature.
Dimensional Compatibility. Adequate provisions for
changes in dimension should consider both the range of
temperatures to be encountered and the likely range in moisture
content. In addition, the dimensional stability of the
insulation relative to the other materials in the roof assembly,
such as the roof membrane and roof deck, should be considered.
Where the change in dimension due to temperature varies
considerably between the insulation and some other component of
the roof assembly, provision should be made to accommodate this
differential change in dimension.
Compatibility. It is important to establish the
compatibility between the insulation and other components of the
roof assembly. When using unfaced plastic foam insulation under
built-up roofing, specify an additional top layer of wood fiber,
fiber glass, or perlite insulation to guard against membrane
Thickness. With the high thermal resistance and low U-
values commonly used for roof insulation, the thickness of
insulation can be a substantial consideration in roof design.
Drawing details should allow adequate space for the insulation's
Layering. When board type insulation is used, it is
often necessary and preferred to have multiple layers. The
insulation boards should be as large as can be practically
handled and the joints should be staggered and offset between
layers. Proper type and length fasteners should be used and
consideration given to possible lateral movement of the roof
insulation. Layering will reduce fastener heat transfer when the
bottom layer is mechanically fastened.
Design Criteria. The energy evaluation of a building
will determine the required thermal resistance or R-value for the
roof by the application of design criteria and analysis of life