Flashing

Flashing creates waterproof barriers through thin, impervious materials that prevent water from entering buildings at joints and intersections. This critical weatherproofing system protects structures from water damage and reduces indoor mold problems

Historical Development

Before manufactured sheets existed, builders used creative methods like angled shingles and mortar flaunching to minimize water penetration. By 1832, detailed instructions for lead flashing installation appeared in builders’ guides, establishing techniques still used today

Material Options

Metal Components

Modern flashing uses various metals including:

• Copper: Offers malleability, strength, and superior longevity
• Aluminum: Light and versatile but vulnerable to salt spray
• Stainless Steel: Excellent for coastal areas
• Zinc Alloy: A newer, environmentally conscious alternative

Flexible Solutions

Contemporary materials include rubberized asphalt, butyl rubber, and acrylic compounds. These materials offer different temperature tolerances and UV resistance levels, though their adhesives aren’t meant for long-term water resistance

Installation Types

Roof Applications

Roof flashing protects discontinuities and protrusions, with valley flashing managing water at roof plane intersections. Chimney flashing combines base and counter-flashing to create reliable water barriers

Wall Protection

Wall flashing embeds within structures to redirect penetrating water outward. Sill flashing under windows and doors prevents water infiltration at these vulnerable points

Environmental Considerations

While lead flashing remains available in the US and UK, newer materials like “soft zinc” offer recyclable alternatives without toxic runoff concerns. The industry continues to balance durability with environmental impact

Critical Design Factors

Proper engineering proves essential as incorrect installation can direct water into buildings rather than away from them. Expansion joints must accommodate thermal movement in metal flashings to prevent deformation. In coastal areas, material selection must account for accelerated corrosion from salt spray.