Undercourse

Definition

An undercourse is a layer of shingles laid beneath an exposed course of shingles at the lower edge of a wall or roof to provide a waterproof layer behind the joints in the exposed course.

Purpose

The undercourse is critical in roofing and siding to prevent water infiltration. It acts as a secondary barrier against water penetration, protecting the structure from moisture damage, leaks, and potential structural degradation.

Examples of Use

• Roofing: In a roof installation, an undercourse of shingles is laid beneath the primary layer to ensure that water running down the roof cannot seep through the joints and cause leaks.
• Wall Cladding: When applying shingles to a wall, an undercourse can be used to enhance waterproofing, especially at the base where water runoff is most likely to collect.

Related Terms

• Flashing: Material used to prevent the passage of water into a structure from a joint or seam.
• Starter Strip: The initial course of shingles or tiles installed at the edge of a roof.
• Underlayment: A layer placed under the main roofing material for additional protection.

Notes

Proper installation of the undercourse is essential to ensure its effectiveness. It should be laid with care to avoid gaps or overlaps that could compromise its waterproofing capabilities.