Slate Roofing

Natural slate roofing enriches the overall appeal of a building while affording more lasting and reliable protection than any substitute. Architects specify our own Vermont roofing slates for their unfading and weathering colors, durability, ‘on-the-grain’ fabrication and high quality standards. And because we produce slate roofing tiles in custom sizes, shapes and thickness, architects also appreciate the flexibility our materials afford them in their designs. Our domestic slates have been widely used for roofing since the early 1800s. A slate roof is an excellent choice for both new construction and historic restoration.

Slate Roofing Projects

Specifications

Products

Many styles of roof are available including uniform lengths and widths, uniform lengths and random widths, graduated lengths and/or thickness, textured roofs, patterned roofs and staggered butts.

We offer copper slater’s nails, stainless steel slate hooks, slate rippers, slate hammers and slate cutters.

Weathering Characteristics

Some materials are “unfading”, meaning they will hold their basic color even after many years of exterior use. Others are “weathering” or “semi-weathering”, meaning they will change color (usually to shades of brown) when used outside. A stone’s weathering characteristic is primarily an aesthetic consideration. “Weathering” in and of itself does not adversely affect the performance or durability of a stone. See stones below for weathering characteristics.

Performance

Our slates have tested ASTM Grade S-1 (highest), are durable (lasting over 75 years), exceptionally strong and hard, have low absorption rates, are dense, acid- and heat-resistant, extremely resistant to freeze-thaw cycles and fireproof.

finishes

Natural Cleft with trimmed edges.

sizes

Standard lengths from 12 to 20 inches. Standard widths from 6 to 14 inches. Custom sizes depend on stone selected, thickness, and other factors. Custom shapes also available.

thickness

Standard thickness is 3/16-1/4 inch. Other common thicknesses include1/4” minimum, 3/8”, 1/2”, 3/4”, and 1”. Custom thicknesses are available.

exposure

A function of shingle length and headlap. Exposure = (length of shingle minus headlap) divided by 2.

nail holes

We generally put the nail holes in the slates at the quarry.

cost estimates

We are pleased to provide quotations based upon quantity surveys, sketches or architectural drawings.

headlap

A function of the pitch of the roof. Standard headlap is 3 inches.

drafting

We are accustomed to working from architectural drawings. Our in-house drafting department is pleased to produce estimates, detailed roof drawings and sketches.

technical support

We are pleased to assist with samples, slate matching services, site inspections, mock-ups, installer recommendations, test data, specifications, technical information and design suggestions.

installation

Generally installed with copper slater’s nails or stainless steel hooks. Contact us for specific sketch details, specifications, recommendations, etc.

maintenance

Minimal. Broken shingles can be easily replaced with the use of a slate ripper.

references

We strongly suggest the seminal work on the subject entitled Slate Roofs, originally published by the National Slate Association in 1926 (not much has changed). A must-have book loaded with photos, sketches, installation details, information on specific slates, etc. Contact us to purchase this book.

Additional Specs

Slate Roofing Specifications

Importance of Grain Direction

It is well-documented that for maximum strength certain strong-grained roofing slates must be produced “on the grain”. This means the long dimension of a piece of roofing slate must run parallel to the grain. “Cross-grained” or “diagonally-grained” roofing slate is significantly weaker than properly fabricated shingles. Slate is like wood in this respect. Imagine the weakness of a cross-grained wooden rafter.

All of our quarrying and fabrication techniques have been designed to produce slate that is “on the grain”. Although this centuries-old method causes us to have higher labor costs and waste factors than companies that produce roofing slate with no regard to grain direction, it results in a better product and significantly less breakage on the jobsite.

As shown below, our slate splits in two directions: 1) along its cleave into layers, and, 2) along its grain. The grain cannot be seen (as opposed to the cleft pattern) and runs in a single direction perpendicular to the cleave. Once a shingle has been produced, it is only possible to determine the grain direction by breaking the piece.

When the blocks of slate are brought to the splitting shed, they’re first crosscut against the grain with a diamond wetsaw. The crosscut blocks are then sculpted, or split along the grain, with hammer and chisel. These blocks are split into smaller blocks which are then halved again and again to produce rough shingles. The rough shingles are then mechanically trimmed and punched or drilled to produce the finished product.

Selection Considerations

There are two issues to consider when specifying roofing slate:

1.) the geology and characteristics of the deposit from which the material will be quarried, and
2.) the quarrying and fabrication processes of the company that will actually produce the material.
All slates do not share the same properties. Deposits vary tremendously in terms of quality, water absorption rates, strength, color variation, weathering characteristics, acid resistance, cleft texture, durability, etc. Our slates will last over 125 years on a roof; others may last only 20 years.
We are committed to producing the highest quality roofing slate. By quarrying and fabricating our own products, we control production at every stage. For strength, we produce our own Vermont roofing slate “on the grain”, meaning the grain direction runs parallel to the longest dimension of the shingle. Our splitting (unless otherwise specified), trimming and punching is consistent and accurate. We are attentive to quality and sort out inferior pieces at several stages of production. And we will certify a particular slate’s weathering characteristics and that it was produced “on the grain”.
We encourage you to get to know the performance characteristics of a certain deposit through test data, track records and references. And visit the quarry. Meet the people who will be responsible for the production of your order. Inspect the quarry and roofing slate production process.