A crawlspace should allow entry for inspection
and maintenance, but inhibit entry of outdoor pests. Whether
it's a continuous foundation or a pier-and-beam with an open
crawlspace, practical and effective methods and materials are
available to impede pests.
Continuous Foundations
In continuous (stem wall) foundations, pest entry is restricted
with properly specified ventilation coverings. The 2003 International
Building Code (Section 1203.3.1) prescribes a variety of
materials for covering ventilation holes, provided the openings
in the covering do not exceed 1/4":
Perforated sheet metal plates not less than 0.070" thick
Expanded sheet metal plates not less than 0.047" thick
Cast-iron grills or gratings
Extruded load-bearing vents
Hardware cloth of 0.035" wire or heavier
Corrosion-resistant wire mesh, with the least dimension
of the openings not exceeding 1/8"
Pier-and-Beam Foundations Figure 4 gives an underfloor view of pest
management strategies for a pier-and-beam system. This figure
illustrates two strategies to inhibit pest entry — either
a perimeter or under-floor barrier. At the foundation perimeter,
pressure-treated decorative latticework backed with corrosion-
and pest-resistant screening can be framed between piers. If
a brick curtain wall is installed between piers along the perimeter,
the opening requirements and coverings prescribed for a stem
wall should be used.
For protection under the floor, a breathable pest barrier is
typically attached at the bottom edge of the joists to prevent
pests from nesting in insulation and damaging wiring or other
systems. Common materials used for this application include:
house wrap, hardware cloth, fiberglass insect screen, plastic
webbing or netting, corrosion-resistant wire mesh, and perforated
vinyl or fiber-cement soffit panels.
