SYSTEMS/METAL BUILDINGS
Thermal Insulation
Metal building systems are often insulated between the inner and outer skins with fibrous or
sprayed foam insulation. Fibrous insulation can suffer from poor thermal performance due to
compression of the insulation by the girts and purlins. These structural elements and other metal
connectors act as thermal bridges with any type of insulation. Two examples of such design
defects and improved alternatives are shown below. These cases are presented for roof purlins,
but also apply to wall girts. Figure 4.6.1 shows a detail in which the insulation is interrupted by the
roof purlins (Steven Winter Associates). In the alternative detail, a spacer of rigid insulation is
placed over the insulation to maintain continuity of the insulation system. In this alternate design,
the insulation should be in close contact with the spacer so there are no air spaces in the overall
insulation system.
ACCEPTABLE
/Steel clip
Insulating
spacer
Figure 4.6.1 Insulation Between Roof Purlins (Steven Winter Associates)
Figure 4.6.2 shows a case in which there is a continuous layer of fibrous insulation, but the roof
purlins compress the insulation, degrading its effectiveness. The alternate detail employs rigid
insulation at the purlin to improve the performance.
ACCEPTABLE
UNACCEPTABLE
Figure 4.6.2 Insulation over Roof Purlins (Steven Winter Associates)
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