Outstanding Beauty Of A Slate Roof

A Slate Roof For Outstanding Longevity & Natural Beauty

Why use slate?

Slate roofing can be applied to any permanent structure. The intrinsic beauty of slate will enhance any building from schools to homes, as well as commercial and government structures.  Slate’s extended life expectancy and durability creates a low cost of ownership.

Slate also provides these benefits:

Natural material

• Fireproof

• Waterproof

• Permanent

• Insulating factor saves energy

• Resists climactic change

• Impervious to fungi and mold

Slate contributes to design elegance through:


• Thickness

• Surface texture

• Overall roof texture

Guaranteed to last one hundred years!

Slate Grades

Slate is “graded” according to the uniformity in thickness that each piece exhibits.  Since slate is a natural product, the more demanding the physical specification, the more the demanding production requirements.  Therefore, a slate’s grade has great bearing on the availability and overall cost of the material.

Important facts about slate…

Slate is a tried and true material for building a beautiful and very long lasting roof for any structure.  The 100 year life expectancy is no projection—it is the result of “field application”. There are thousands of slate roofs still in service today installed in the 1800’s!  With such a long history, many terms describing the material have been coined and over the years, and some have evolved into misinterpretation.  For example, a common misconception associated with the nomenclature of describing slate occurs when the terms weathering and fading are erroneously interchanged.  Here’s the clarification:

Nomenclature of Blue Black & Black Slates


The term fading refers to certain slates, that after prolonged exposure to the elements, exhibit a chalk-ashen residue on the exposed surface of the slate.  The chalk-ashen residue is the result of a chemical reaction and the associated release of calcium from the body of the slate.  This release weakens the structure integrity of slate and is detrimental to the slate’s life expectancy.  The term is most often used in conjunction with the Blue Black or Black slates of Pennsylvania and Virginia.

Non-fading or Unfading

The term refers to certain slates that after a prolonged exposure to the elements do not produce the chalk-ashen residue.  Non-fading or Unfading slates usually have greatly extended life expectancies over those slates prone to calcium release.

Classification of Colored Slate

Colored slate does not fade, but it will experience varying degrees of color change.  This weathering of slate is due to the oxidation over time of minerals embedded in the slate.  Depending on mineral content, the weathering process slowly changes the slate color.  The color change is often a movement toward buff, brown, gray or tan.  This surface oxidation is not detrimental to the slate’s structural integrity and does not shorten the life of a roof.

Colored slates are classified in three types.  This classification is based upon the degree of color change  over time:


The term refers to slates that will exhibit the largest number of individual pieces that will transform from the original color to an earth tone.


The term refers to slates that exhibit the least amount of color change.


The term refers to roofing slates that are manufactured from slate that has varying mineral content.

Some of these slates will undergo a color change while others remain their original shade.  The percentage of semi-weathering slates that will experience color change is variable depending upon the location in the quarry from which the slate was extracted.

If you would like more information, contact a Minnesota roofing contractor that is experienced in slate roof installation.


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