Slate is one of the most durable roofing materials, although the need for roof repairs does still arise. The aesthetic appeal of a slate roof is another plus, especially on homes featuring French, Italian or English Tudor architectural influences.
Longevity of Slate
Some Maryland residents embrace the use natural slate for historic reasons, while others appreciate the fact that a properly installed slate roof can easily last many decades. Even softer slate can last 60 years or more, while various New York and Vermont slates can last 125 years. Slates from parts of Virginia may have a life span exceeding 175 years.
American Tradition of Slate Roofs
Natural slate roofing has been in use in America since the 17th century. Archeologists discovered evidence of slate roofing at the historic Jamestown settlement that dates to the period 1625-50. By the late 17th century, New York and Boston ordinances recommended slate roofs.
Historically, there were three kinds of slate roofs: standard, graduated and textural. Textural slate is more common on Tudor buildings where more heavily textured slate of varying thicknesses and colors adds to the architectural impact. Graduated slate roofs are less common on homes. Larger structures benefit from the use of larger, thicker slate at the bottom of the roof, and small, thinner slate near the top.
Slate Weathering and Deterioration
Over time, freeze-thaw and wet-dry cycles slowly impact slate tiles. Impurities in the natural slate tiles are usually the issue. Chemical reactions between calcium and water form gypsum. The molecules occupy more space than the original calcium molecules, and this pushed layers apart, causing delamination. Leaching on the underside of a tile often causes more rapid deterioration there, where it is often less visible to the untrained eye. Moisture retention on the underside of tiles may cause rotting of the wood sheathing underneath.
Scaling and chipping occurs along the cleavage planes of slate tiles. Sometimes, tiles become spongy as inner layersdelaminate. A sound test is sometimes used to establish the condition of slate tiles. Newer, intact tiles will emit a clear, solid sound when lightly struck, while weathered tiles may only generate a dull, ill-defined thus when struck.
The more the slate deteriorates, the more moisture it absorbs. Such tiles are more vulnerable to freeze-thaw, hot-cold and wet-dry cycles. In general, dense slates are less subject to calcium-centered deterioration than more porous slates.
Roof pitch will also impact the effective life of a slate roof. More steeply pitched roofs shed water more efficiently, reducing the impact of moisture. Portions of a slate roof prone to ice damming will often deteriorate faster. Areas of concentrated water flow will also subject slate tiles to more stress.
Slate Roof Repair
The most obvious cause of cracked tiles is a falling tree limb. However, ice dams can also crack tiles. Occasionally, a worker walking across the roof can crack tiles. Whatever the reason, prompt replacement of damaged slate avoids more serious leaks and damage.
The extreme durability of slate means that flashing, valleys and gutters will often develop problems faster than the slate itself. Flashing may fail due to pinholes, misalignment, looseness and open seams. This means that leaks are often resolved with little or no slate tile replacement.
Copper and stainless steel nails will typically last the life of the roof. However, regular steel or even galvanized nails may rust out over time, leading to missing tiles. When asphalt and cedar shake shingles are nailed down, they are securely fastened. With slate tiles, nails are not driven tight. Rather, the slate tile should hang loose on the nail shank. In fact, a nail driven too far may cause the tile to crack. On the other hand, a protruding nail may puncture the tile directly above it.
Only a properly equipped, experienced slater has the knowledge and expertise to install or repair a slate roof so that it is both watertight and attractive.
If your slate roof is in need of inspection and/or repair, the professionals at BRAX Roofing stand ready to assist. Please contact us today to arrange for a complimentary, no-obligation estimate.