Slate roofs have been around for hundreds of years. Slate is a natural roofing material historically used in the Northeastern United States. In recent years the use of slate as a roofing material has become more widespread throughout the country. The classic, natural look of a slate roof provides a lovely aesthetic appeal. Properly installed slate roofs are nearly indestructible; it is not uncommon for the slate roofing to outlast underlying roof structures. This high-end roofing material typically installs for around $850 per square, which represents a 10’x10′ section. It should be noted that the installation of a slate roof is considered a specialty and requires specific tools, skills and experience. Exercise care when selecting a roofing contractor to install a slate roof system.
Slate roofing is available in varying shades of grays, reds, and greens. The color of the slate varies depending on the geographic area from which the slate was quarried. Certain types of slate will change appearance as they age, these are known as weathering slates. Other slate roof tiles, called permanent or unfading slate, remain mostly true to their original color. Semi-weathering slate roof tiles will change somewhat over their lifetime and offer a middle ground in terms of weathering. Some slate roofing tiles have a smooth appearance while others have a rougher looking texture. These variations are a matter of personal preference. When selecting slate roofing materials be sure to look at a variety of different slates and choose the one that best matches your home’s facade.
Slate roofs are made of dense, hard, fine-grained rock which is mined or quarried from the ground. The material is then split into thin slabs to be used as roofing shingles. Nail holes are punched into the slate shingles during manufacturing.
Slate roofing is unique in that, should the need for repairs arise the roof can be taken apart, mended, and then reassembled. Be sure to have all repairs done by a slate roof installation expert who will possess the knowledge, skills and tools needed to properly maintain damaged areas while ensuring the continued integrity of your entire slate roof system.
Slate roof shingles are incredibly durable and can easily provide a century of use when installed correctly. Slate roofs are highly leak-proof and have a Class A fire rating.
Installation requirements for slate roofing:
Roof Deck: According to the NRCA slate roof shingles should be applied over closely spaced wood planks or continuous wood decking. It is recommended that plywood decking be at least 5/8 thick nominal exterior-grade. The NRCA recommends using caution when installing a new roof onto a roof deck made of OSB, preservative-treated wood, and wood treated with a fire-retardant coating. A qualified roofing contractor can provide information on appropriate roof decking materials for your roofing needs.
Underlayment: The underlayment provides temporary waterproofing during roof installation and acts as a permanent secondary waterproofing layer to the outermost roofing material. The century-long lifespan of slate roofing tiles require an underlayment with a comparable service life. It is not uncommon for slate roofs to outlive their underlayment felt, although the ability of the slate roof tiles to be removed and reinstalled facilitates necessary underlayment repair and replacement without the expense of a new roof purchase. The NRCA recommendations for underlayment, commonly called “felt paper” specify a minimum of one layer of No. 30 asphalt-saturated felt applied horizontally in shingle fashion on roof decks having a slope of 34 degrees or more. A minimum of two layers of No. 30 asphalt-saturated felt paper is recommended for roof decks with a slope between 18 and 34 degrees. Installation of slate roof systems with a slope of less than 18 degrees is not recommended. For extremely cold climates the installation of an ice-dam membrane may be required. Check with a qualified roofing contractor for information about this additional underlayment.
Fasteners: Roofing nails used to install slate shingle roofs should be sharp-point, 3/8 inch large flat head nails. They should be made of copper-wire slating or stainless steel. Hot dipped galvanized nails may also be used. Aluminum nails and electro-galvanized nails should not be used on slate roof shingles. The nails used to install slate shingles should be long enough to fully penetrate all layers of roofing materials and reach into the underside of the roof deck. A minimum of two nails per slate should be used to install slate shingles, although four nails per slate may be required for areas of high wind or for thicker cut slate shingles.
Flashing: When installing slate roof systems flashings should be installed around the perimeter edge, at any penetrations, in open valleys, and along vertical surfaces. Flashings should be made of non-corrosive materials such as copper or terne-coated stainless steel.
The NRCA recommends the use of slate shingles that comply with American Society for Testing Materials (ASTM) standards- ASTM C406. These standards govern the physical properties and components of slate shingle roofing materials. Carefully read shingle packaging and product literature to determine which slate shingles have met the standards laid out by the ASTM. Bad slates are available and the best way to verify the quality level of potential slate roofing materials is through historical analysis. In addition a simple grading system exists by which the expected lifespan of slate can be determined. Slate that will last more than 75 years is graded S-1, slate meant to last between 45 and 75 years has a grade of S-2, and S-3 slates are not meant to last more than 45 years.
Slate roof shingles come with warranties against manufacturing defects and failure of the slate itself. Your roofing contractor should provide you with detailed warranty information pertaining to the specific slate roofing shingles you select, as well as warranties offered by the contractor to cover roof installation. Hiring a roofing contractor experienced in the specialized installation of slate roofs is highly advised.