How to File an Insurance Claim for a Hail Damaged Slate Roof

In Educational Articles by Black Diamond Slate


After a hail storm, your slate roof may be damaged. Here is how to assess your roof and file an insurance claim. Hail damage can show itself in a number of ways, you will not always see “bullet holes.” Many times it’s edge breaks and cracks. The key is to find fresh breaks identified by the lack of aging and dirt on the slate underneath. Breaks from hail impacts can be in the body of the slate or along the edge, but may not be as visible if it does not totally dislodge the broken slate. Slate that has only been on the roof a decade or two is harder than older slate which can soften over time. New slate is not likely to show bullet hole type damage. In this case, the impact creates linear fractures in the slate as opposed to holes. These fractures can only be identified through close inspection and will not be visible from the ground.

A slate roof can have thousands of these fractured slates and be a total loss even though the roof appears normal from the ground. In many cases this damage is overlooked. However, during the first large wind event or heavy freeze combined with some moisture, the roof will shed the broken slate in large numbers. It is important to understand that these fractures will hold moisture and expand in freezing temperatures. Slate is the longest lasting roofing product because it is highly resistant to moisture absorption. However, once moisture is allowed to penetrate the surface though a crack and freeze, slate is extremely susceptible to breakage because it has zero elasticity. As the moisture freezes and expands, it simply continues to break the slate.

There are only two ways to repair a broken slate. The first is using a fastener called a slate hook which is the most common method but is visible from the ground. The second is called using a “bib” where the slate is drilled and nailed down and then a copper sheet is placed over the nail holes. This method is less visible from the ground but takes more time and effort. In the case of slate hooks, it is considered acceptable to use two or three in a square, but anything above that number or close to a valley or drip edge should be avoided. Slate hooks will catch and cause debris to collect on the roof and are difficult to remove once it is caught in the hook.

A roof that looks normal from the ground immediately following a large hail storm can look totally different after one winter cycle or a wind event dislodges the broken slate and causes shedding.

Replacement vs. Repairs
By slate industry standards, anything over 8% to 10% damaged is not considered repairable. The most common size slate on residential construction is 16” or 18” long slate, but it can go down to 12” length in some areas. So for instance, on a 50 square roof with 16×10 slate, there are approximately 13,320 slates. If more that 10% or 1300 slates are broken, it is not feasible to attempt repair unless the damage is concentrated in a certain area. In some storms, only one side of the house might sustain damage. So it may be appropriate to replace one side of the house and repair the other. In this case it is important to select the right slate to match the existing size and color.

Issues for Claims – Every job has to be negotiated

  • Standard Form in Xactimate- Labor rate per SQ does not properly recognize differences in installation
  • Standard Pattern vs Graduated or Staggered
  • Ridge and Valley Details-Open vs Closed Weaved
  • Multicolor Blend vs. Single Color
  • Job Difficulty-Roof access extremely important with slate, # Valleys
  • Color-Purple, Red can be twice the cost of other colors. Know the color before you quote the job.

Identify the slate size (lengths and widths), exposure and style of installation. The standard installation is less expensive to repair or replace than the staggered installation and the heavy thickness. For color selection, send photos to Black Diamond Slate for ID and proper match.

Slate Colors – What’s the difference?
Every customer has different expectations. When they spend the money for slate we want to make sure it is right the first time. Mistakes are expensive. Knowing the colors and where they are is a huge asset in giving the customer what they want. There are an unending number of colors and qualities of slate, mainly dependent on the region of formation. Color and weathering characteristics are a function of microscopic layers of minerals found between the layers of sediment.

Slate in the 21st Century

  • Vermont slate constitutes about 67% of slate installed in US today.
  • The depletion of Unfading Black stone of available from Pennsylvania and Maine (such as Bangor, Peach Bottom and Monson slate) has created a need for non-fading and non- weathering black from other countries to replace and repair dark gray and black slate prominent in the Northeastern US.
  • Spain, the largest producer of roofing slate (80% of all roofing slate produced world wide), and offers very high quality (S-1 grade) non- weathering, non-fading gray and black.
  • China and Brazil have huge reserves of all the main colors but quality varies a great deal. While China and Brazilian slate are acceptable and even desirable in certain climates like southern California and Texas, it is not suitable for colder climates in the northeast.

Quality of Imports vs. Domestics

  • As with domestic slate production, both good and bad slate can be sourced abroad. Vermont produces S-1 and S-2 grade slate and PA Black is mainly S-2 while the old Peach Bottom was probably one of the best S-1 UFD Blacks ever. The same is true for all of the foreign producers.
  • Both S-1 and S-2 Grade slate is allowed for roofing. ASTM Tests for slate have been under fire for years and remains in controversy. However testing is important as a bench march for imports. Water Absorption, Weather (Acid Resistance), Modulus of Rupture

Understanding the Difference Between Good Slate and Bad

  • Iron and unstable Pyrite is the main defect found in imported and domestic slate.
  • Only accept S-1 Grade slate and ask for the test data.