additional vents unless they sold for significant-
RECOMMENDATION
ly less than their current selling price. (Inci-
More effective use should be made of the roof
dentally, feedback from potential vent users in
blister vent. In the DoD community, and probably
the private sector indicated the same feeling
elsewhere, too few are aware of the vent, and those
about price.) A roof with 100 blisters would re-
that are choose not to use it, primarily due to cost,
quire 0 in vents. Projected to an installation
even though economics suggests that blister vents
level, with numerous roofs involved, the large
are cost-effective. To increase use, an extensive
number of vents required represents a significant
education project informing potential users of the
investment. Thus, the largest barrier to more use
true cost of blisters must be undertaken, or the
of the vent seems not to be with the technology
price of the vent must be reduced, or both. Since
but with its current price.
most people who are aware of the vent agree that it
is technically sound, reducing its selling price sig-
nificantly seems to be the logical first step toward
CONCLUSION
overcoming current resistance to use of the blister
Blisters are a leading cause of problems on bi-
vent. However, selling price alone is not expected
tuminous built-up roof membranes (LaValley
to be enough, so concurrent efforts to advertise
1994). They weaken the roof membrane, acceler-
and demonstrate the vent are also needed.
ate its aging, and increase its vulnerability to
puncture. They shorten roof life.
Blister vents are the only proactive alternative
LITERATURE CITED
to cutting out and patching blisters. Once in-
LaValley, A.L. (1994) NRCA's market survey shows
stalled, the vents stop blister growth by deflating
industry rebound is on the horizon. Professional
the blister and causing its raised portion to col-
Roofing, April.
lapse onto the roof where it is less likely to be
Cullen, W .C. (1993) Project Pinpoint Analysis: Ten-
damaged. Blister vents can postpone the cost of
Year Performance Experience of Commercial Roofing
reroofing when used early. Although the vents
19831992. National Roofing Contractors Asso-
cannot prevent blisters from happening, they can
ciation, 10255 W. Higgins Road, Suite 600, Rose-
lengthen the service life of a roof.
mont, Illinois 60018-5607.
Despite the positive impact that wide use of
Korhonen, C. (1986) Blistering of built-up roof
the vent could have on built-up roof mainte-
membranes: Pressure measurements. USA Cold
nance costs, the vent is underused, primarily be-
Regions Research and Engineering Laboratory,
cause it is viewed as being too expensive, but
Special Report 86-29.
also because of a lack of awareness of the vent in
Korhonen, C. and J. Bayer (1986) ROOF blister:
the roofing community and a reactive attitude
Physical Fitness Building, Fort Lee, Virginia. USA
towards repair.
Cold Regions Research and Engineering Laborato-
ry, Special Report 86-35.
RIEI (1980) Roof Maintenance Manual. Roofing In-
dustry Educational Institute, 6851 S. Holly Circle,
Suite 250, Englewood, Colorado 80112.
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