What Is a Lath in USA

Introduction to Lath in American Construction

In the United States construction industry, the term lath refers to a structural framework or support surface used beneath finishing materials such as plaster, stucco, or other coatings. A lath provides a textured surface onto which the finishing material can adhere properly, enhancing the durability, stability, and aesthetic quality of the wall or ceiling. For decades, lathing has played an integral role in residential, commercial, and industrial construction.

Historical Background of Lath in the USA

Historically, wood lath was the first material commonly used in U.S. building practices. These were narrow, horizontal strips of wood nailed to wall studs and spaced slightly apart to allow plaster to seep into the gaps, hardening into a rigid, durable wall finish. This method dominated from the late 18th century through the early 20th century.

As construction methods advanced, gypsum lath, and then metal lath, gradually replaced wood due to their fire resistance, ease of installation, and structural integrity. Today, the U.S. construction industry uses a variety of modern lathing materials, depending on the application and environmental conditions.

Types of Lath Used in U.S. Construction

Metal Lath

Metal lath is now the most prevalent lath type in the United States. It is made from galvanized or stainless steel, formed into a mesh pattern. Common variants include:

• Expanded Metal Lath: Cut and stretched to form a mesh, ideal for three-coat stucco or plaster applications.
• Self-Furring Lath: Features built-in dimples or embossing that hold it slightly away from the substrate, improving plaster penetration.
• Rib Lath: Reinforced with V-shaped ribs for use in ceilings or large spans.
• Paper-Backed Lath: Combines metal mesh with a weather-resistant barrier, frequently used in exterior wall assemblies.

Gypsum Lath

Also known as rock lath, this is a gypsum board that’s specially treated to bond with plaster. Commonly used in fire-rated construction, gypsum lath offers a more modern and convenient alternative to traditional lath-and-plaster systems.

Wood Lath

Still visible in historic homes across the U.S., wood lath comprises thin wood slats typically measuring 1/4 inch thick and 1 inch wide. They are spaced with small gaps to allow wet plaster to grip the wood structure. Though rarely used in modern projects, wood lath remains vital for restoration and preservation efforts.

Plastic or Composite Lath

Plastic lath is lightweight, non-corrosive, and suitable for high-moisture environments such as coastal areas. It is increasingly common in EIFS (Exterior Insulation and Finish Systems) and modern synthetic stucco applications.

Core Functions of Lath in Construction

Bonding Substrate

The primary role of lath is to provide a mechanical base that allows plaster or stucco to attach firmly. The open structure of the mesh or slats permits the material to key into the lath, forming a strong, cohesive finish.

Moisture Barrier Support

In exterior systems, lath often works in conjunction with moisture barriers or drainage planes. When paired with building paper or a WRB (Weather Resistant Barrier), lath helps prevent water intrusion and promotes proper drainage.

Crack Resistance

Properly installed lath reduces the risk of cracking and delamination, ensuring a uniform surface that maintains its integrity over time, even under thermal expansion and building movement.

Fire Resistance

When part of a fire-rated assembly, certain lath systems—particularly gypsum or metal lath—contribute significantly to a wall’s fire protection rating, a critical factor in meeting building codes.

Applications of Lath in the U.S. Construction Sector

Residential Construction

Lath is extensively used in single-family homes, particularly for stucco siding in Southwestern states such as California, Arizona, and Nevada. Interior applications include decorative plaster ceilings and curved wall designs.

Commercial Buildings

Office buildings, schools, and apartment complexes use lath in fire-rated partitions, sound-dampening walls, and aesthetic finishes. Gypsum lath remains popular due to its cost-effectiveness and code compliance.

Restoration Projects

In heritage buildings, especially from the 19th and early 20th centuries, preserving or replicating wood lath systems is essential to maintaining historical authenticity while updating structural integrity.

EIFS and Modern Cladding

In energy-efficient wall systems, lath plays a supporting role beneath foam insulation and synthetic stucco, providing the necessary anchoring for these advanced materials.

Installation Best Practices in the U.S.

Substrate Preparation

Before installation, the wall or ceiling framing must be plumb and securely fastened. For exterior applications, a WRB or drainage plane is installed over the sheathing.

Fastening Requirements

Lath must be fastened with galvanized nails, screws, or staples, ensuring full penetration into the studs or joists. Fasteners are typically placed 6 inches on center along framing members.

Lapping and Spacing

Proper lapping of adjacent sheets—typically 1/2 inch end lap and 1 inch side lap—prevents cracking and ensures system continuity. Control joints are added every 100–144 square feet to accommodate movement and stress relief.

Accessories

Essential components include:

• Corner beads for straight, reinforced corners
• Weep screeds for moisture drainage
• Expansion joints in long wall runs or transitions

Building Codes and Standards

• ASTM C847: Standard specification for metal lath.
• ASTM C1063: Standard for installation of lathing and furring.
• ASTM C37 and ASTM C1396: Standards for gypsum lath.
• International Building Code (IBC) and IRC (International Residential Code): Outline fire ratings, moisture control, and installation practices.

These codes ensure that lath assemblies meet structural, moisture, and fire safety requirements across all U.S. jurisdictions.

Modern Innovations and Trends

Integrated Lath and Barrier Systems

Manufacturers now offer pre-combined lath and WRB rolls, reducing labor time and enhancing water protection.

Corrosion-Resistant Composites

Fiberglass-reinforced lath and polymer mesh alternatives are growing in popularity for salt-air coastal environments and LEED-certified projects.

Digitally Designed Assemblies

Some large-scale commercial projects utilize BIM (Building Information Modeling) to plan lath layouts, optimize material usage, and coordinate with other trades.

Regional Use and Preferences

• Southwest USA: Prefers stucco over metal lath for durability in arid climates.
• Northeast & Midwest: More use of gypsum lath in commercial and multifamily projects.
• Southeast: Employs plastic lath and advanced WRBs for hurricane-resistance.
• Pacific Northwest: Prioritizes moisture drainage systems and fire-rated assemblies in lath installations.

Conclusion

A lath, in the context of U.S. construction, is more than a structural layer—it is a critical building component that affects everything from aesthetics to code compliance. Its ability to support plaster, stucco, or other finishes while managing moisture, ensuring fire safety, and maintaining durability makes it indispensable in both traditional and modern architectural systems. From wood slats in historical homes to fiber-reinforced mesh in contemporary high-rises, the evolution of lath reflects the demands of ever-advancing construction standards in the United States.

End of article.