What’s a Lath in Construction in USA

Understanding Lath in American Construction

In the construction industry of the United States, a lath refers to a thin, narrow material—traditionally wood, but now also metal, gypsum, or plastic—used as a foundation layer to support coatings such as plaster, stucco, or cement render. This system provides a textured surface for the wet material to adhere to and has been a critical element in American building practices for over a century.

Lath is most commonly used in both interior wall systems and exterior cladding, forming the substrate that ensures proper adhesion and structural integrity of the finish material. Whether in historic wood-framed houses or modern steel-frame commercial structures, lathing remains a crucial construction method in the U.S.

Types of Lath Materials Used in the USA

1. Metal Lath

Metal lath is the most common type used today, favored for its durability, fire resistance, and excellent bonding properties. It includes:

• Expanded Metal Lath: A steel sheet that’s slit and stretched into a mesh. It provides a strong mechanical bond for stucco and plaster.
• Ribbed Lath: Reinforced with ribs for structural rigidity, ideal for ceilings or curved surfaces.
• Self-Furring Lath: Engineered with indentations to create a consistent space from the substrate, allowing proper plaster embedment.
• Paper-Backed Lath: Combines metal mesh with a moisture-resistant barrier, often used in exterior wall assemblies.

2. Gypsum Lath

Gypsum lath, also called rock lath, is a panel product made of a gypsum core with treated surfaces that help plaster bond effectively. It’s commonly used in fire-rated walls and is a standard component in commercial drywall systems.

3. Wood Lath

Wood lath is a traditional method, consisting of narrow, horizontal strips of wood nailed to wall studs. Though largely obsolete in new construction, it remains relevant in restoration and historic preservation projects across the U.S.

4. Plastic Lath

Plastic or polymer lath is a lightweight and corrosion-resistant alternative to metal, ideal for coastal or high-humidity environments. It is compatible with synthetic stucco systems and used in EIFS (Exterior Insulation and Finish Systems).

Functions and Purpose of Lath in Construction

Structural Support for Finishes

Lath provides the physical base that supports layers of plaster or stucco, enabling them to be applied evenly, adhere securely, and cure properly.

Keying Surface

The mesh or texture of the lath creates mechanical keys where wet materials seep into the gaps, harden, and form a permanent bond.

Fire Resistance

Certain types of lath, particularly metal and gypsum-based, contribute to fire-rated assemblies, helping meet building code requirements for fire containment.

Moisture Management

Paper-backed or moisture barrier–integrated laths prevent water infiltration, a crucial feature for exterior wall applications.

Where Lath is Used in U.S. Construction

Exterior Stucco Systems

Lath is an essential component of three-coat stucco systems. In regions such as California, Florida, Arizona, and Nevada, where stucco exteriors are popular, lath provides the base for applying the scratch, brown, and finish coats.

Interior Plaster Walls and Ceilings

In luxury homes, custom builds, and historic buildings, interior plasterwork is still used. Lath ensures these finishes are both aesthetically seamless and structurally durable.

Commercial Fire-Rated Walls

In hotels, schools, and apartment complexes, gypsum lath is used behind plaster or drywall to provide fire-rated partitions and meet life safety codes.

Curved or Ornamental Surfaces

For vaulted ceilings, arches, and decorative cornices, flexible lath (like ribbed metal) enables artisans to shape plaster in complex geometries.

Installation Process of Lath

Surface Preparation

The wall or ceiling framing must be clean, level, and securely fastened. In exterior applications, a weather-resistant barrier (WRB) is installed beneath the lath.

Lath Attachment

• Metal lath is fastened with galvanized nails, screws, or staples.
• Proper spacing is critical: Fasteners must penetrate at least 3/4 inch into wood studs or 3/8 inch into steel framing.
• Overlap requirements: Ends must overlap 1/2 inch, and sides must overlap at least 1 inch to ensure continuity and reduce cracking.

Accessories and Reinforcement

• Control joints are integrated every 100–144 square feet.
• Corner beads and weep screeds are installed at openings and base levels to manage water flow and stress transitions.

Inspection and Code Compliance

Before applying plaster or stucco, lath installations are typically inspected for:

• Fastening integrity
• Proper overlap and placement
• Inclusion of necessary joints and barriers
• Conformance to ASTM C1063 and local building codes

Codes and Standards for Lath in the U.S.

• ASTM C847: Governs specifications for metal lath.
• ASTM C1063: Covers installation of lathing and furring.
• International Building Code (IBC) and International Residential Code (IRC) include detailed regulations for fire-resistance, moisture barriers, and material quality.
• Regional adaptations apply in seismic zones such as California or hurricane-prone areas like Florida, demanding higher installation standards.

Advantages of Using Lath in Modern Construction

Durability and Performance

Properly installed lath ensures long-lasting finishes, capable of withstanding moisture, impact, and thermal expansion.

Enhanced Fire Protection

Gypsum and metal lath assemblies are fundamental to meeting hourly fire rating requirements, making them indispensable in commercial and multifamily builds.

Improved Finish Quality

Lath allows plaster or stucco to be applied in a way that minimizes cracks, improves appearance, and offers a consistent texture across surfaces.

Adaptability

With different lath types available, systems can be tailored for interior walls, exterior cladding, curved structures, or acoustic performance.

Modern Innovations in Lathing Systems

In response to industry demands for faster installations, environmental sustainability, and improved energy efficiency, lathing has seen key innovations:

• Prefabricated panels with integrated lath and WRB
• High-strength composite laths offering corrosion resistance and lower weight
• Smart systems capable of monitoring moisture and wall performance
• Fire-treated lath assemblies for use in high-rise construction

These advancements streamline the construction process while complying with increasingly complex codes.

Regional Considerations in Lath Application

West Coast (California, Oregon, Washington)

• Emphasis on earthquake resistance
• Predominant use of three-coat stucco systems
• High compliance with wildfire codes, requiring non-combustible lath

Southwest (Arizona, New Mexico, Nevada)

• Heavy use of stucco over metal lath due to desert climate
• Need for UV- and heat-resistant barriers

Southeast (Florida, Gulf States)

• Focus on hurricane resilience
• Use of plastic lath and enhanced moisture control systems

Northeast and Midwest

• More common to find gypsum lath in multi-family housing
• Cold weather installations require freeze-thaw durability

Conclusion

In the context of U.S. construction, the question “what’s a lath?” is best answered by understanding its critical role as the foundational layer in plaster, stucco, and render systems. Whether installed in wood-framed homes, steel commercial buildings, or historic landmarks, lath supports structure, aesthetics, and code compliance. With a diverse range of materials—metal, gypsum, wood, and plastic—builders across America rely on lath to meet performance, durability, and regulatory expectations in projects large and small.

End of article.