The primary difference between a purlin and a lath lies in their thickness and orientation when installed. Based on information regarding building materials, purlins are 2” thick wooden strips, which are laid on edge, while laths are up to 1” thick and are laid flat. These distinct characteristics determine their respective applications in construction, primarily in roofing and wall systems.
Understanding Purlins and Laths
Both purlins and laths are essential structural components used in building construction, typically serving as support elements for external finishes like roofing tiles or plaster. However, their specific dimensions and how they are installed lead to different roles and load-bearing capabilities.
- Purlins: Generally larger and stronger, purlins provide structural support spanning between larger rafters or trusses. They form a secondary framework onto which roofing materials or their underlayment are attached.
- Laths: Smaller and lighter, laths are historically used as a backing for plaster (lath and plaster walls) or as the immediate battens onto which roofing tiles or slates are fastened.
Key Distinctions Based on Reference
The most fundamental differences, as highlighted by construction definitions, are their size and how they are positioned:
- Thickness: Purlins are specifically noted as being 2 inches thick, providing substantial depth for structural support. Laths, on the other hand, are significantly thinner, measuring up to 1 inch in thickness.
- Orientation: Purlins are installed "on edge," meaning the 2-inch dimension is vertical, maximizing their strength against downward loads. Laths are laid "flat," with their wider dimension parallel to the surface they are attached to (wall or roof slope), creating a continuous surface for the finish material.
These differences are crucial for their load-bearing function and suitability for various tasks within a building project.
| Feature | Purlin | Lath |
|---|---|---|
| Thickness | 2 inches | Up to 1 inch |
| Orientation | Laid on edge (2" dimension vertical) | Laid flat (wider dimension horizontal) |
| Primary Use | Secondary roof supports, wall girts | Backing for plaster, roof tile battens |
Common Applications
The difference in thickness and orientation dictates where each material is typically used:
- Purlins:
- Used in roofing to support the roof deck or cladding between rafters or trusses.
- Also used as horizontal girts in metal-framed walls to support siding.
- Provide structural stability over longer spans.
- Laths:
- Historically used extensively as a base for interior plaster walls and ceilings (lath and plaster systems).
- Used on roofs as battens to provide a fixing point and spacing for tiles or slates.
- Can be used for creating lattice work or non-structural screening.
In essence, purlins are heavier-duty structural members compared to the more slender laths, which serve primarily as fastening points or plaster bases. Understanding these basic differences is key when working with traditional building materials.
