National Slate Association (NSA)

The National Slate Association (NSA) is a non-profit organisation in the United States that brings together slate quarries, roofing contractors, consultants, architects and suppliers working with natural slate roofing. An association under this name started in 1922. It later became inactive and was reformed in 2002. The association lists a business address in Falconer, New York, and its website is slateassociation.org.

History

In the early 20th century, slate was a major roofing material in the eastern United States, with quarries in Pennsylvania, Vermont, New York, Virginia and Maine. Slate use later declined as cheaper roofing materials spread, and the original association did not continue. A new association under the same name was formed in 2002, at a time of renewed interest in slate for restoration and new construction.

Publications

• Slate Roofs: Design and Installation Manual. The NSA's main publication sets out recommended practice for designing, installing and repairing slate roofs in North America. It covers slate grading, headlap, fastening with copper or stainless steel nails, flashing details and roof deck requirements.
• Slate specification guide for architects and specifiers.
• Technical bulletins and a mobile field guide for contractors.

Why guidance matters

A well-made slate roof can last a very long time, but performance depends on details. Common problems include using the wrong nails, nailing too tightly, insufficient headlap on low pitches, and mismatched replacement slates. Because many slate roofs are on older or listed buildings, repairs often need to match the original slate source, size and colour.

International context

Slate roofing traditions are strong in Wales, Spain, France, Germany and Brazil, each with its own sizes and fixing methods. European slate is covered by the standard EN 12326. The NSA focuses on North American practice, but it shares interests with groups such as the Slate Roofing Contractors Association of North America and European slate federations.