MIL-HDBK-1001/5A
Fahrenheit (F) (66 degrees C) can be reached. Temperature ranges of more than 100 degrees F (38 degrees C) can be experienced in a single day.
3.2.3.2 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.
3.2.3.3 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.
3.2.4 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 blistering.
3.2.5 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 thickness.
3.2.5.1 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.
3.2.6 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
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