Slate Roof Estimation

Follow these steps to determine how much slate you will need for your project. We are always glad to help with slate roof estimation, call us at 800.619.4333 with any questions. You can also use our “Quick Bid” form to assist with getting a quote.


  1. Obtain the net area of the roof in square feet, adding 6″ to rafter length to allow for waste of normal roof.
  2. Deduct one-half of the area of chimneys and dormers if over 20 sq. ft., and deduct 20 sq. ft. less than actual area if more than 80 sq. ft.
  3. Include areas of dormer roofs, sides of dormers if slated, slate saddles, or any other places where slate is used in addition to the main roof area. Included overhanging parts of dormers, etc.
  4. Add 1 sq. ft. for each linear foot of hips and valleys, for loss in cutting and fitting.
  5. Allow from 2% to 15% additional slate, depending upon the extent to which the roof is intersected by other roofs, dormers, walls, other contingencies, etc.
  6. Divide the above total by 100, which will give the number of “squares” of roofing required. It should be noted that slate is always sold at the quarry on the basis of the quantity required to cover “100 sq. ft.” or a “square” of roof when slate is laid with a 3″ head lap. If the roof is flat or other than 3″ lap is used, the quantity must be corrected to the equivalent amount required as though the 3″ lap was used.

Specifying Slate: AIA Section 07315

For your convenience we provide a standard document in Microsoft Word® format as a basis for specifying slate for your projects. Click here to download.


Slate Sizing Chart

We are ready to assist with selecting and specifying slate, advising on installation, or installation techniques.

Call us at 800 619 4333 or click here to contact us.

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