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.
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″
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.