Since the fall of 2004, much of my work has been related to wind
investigations and the writing of wind design guides for the
Federal Emergency Management Agency (FEMA). In addition to
hurricane investigations, I've also investigated several roofs that
have been damaged by other types of storms. The hurricane and
non-hurricane investigations have led me to pay particular
attention to attachment of insulation, base flashings and rooftop
Adhering insulation to cast-in-place concrete is a challenge for
designers and contractors. Because of decks' undulating nature,
insulation boards can bridge across deck depressions. Although some
lack of attachment is expected and not detrimental to wind-uplift
resistance, if the unattached area is large, resistance may be
impaired (see Photo 1). The
following recommendations also apply when a vapor retarder is
between a deck and insulation.
Planar flatness is key to achieving adequate attachment over
cast-in-place concrete decks. I believe most cast-in-place roof
decks are not as flat as desired for fully adhered applications.
For new construction, FEMA 577 recommends a planar flatness of a
maximum 1/4-inch gap under a 10-foot straight edge be specified
when insulation boards are to...
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