Slate’s reputation for durability is accurate to a point, but even the highest-quality slate fails eventually and must be replaced. A roofing expert can tell you how long each type of slate will last, but if you don’t know what type is featured on your new home or when it was installed, simply calculating its age isn’t an option. Nor can you conclude that a handful of failing tiles is cause for replacing the entire roof. Still, you can determine whether to repair or replace your roof by examining it, if you know what to look for.
Look for moisture damage in the attic and on the rafters. Brittle, soft or otherwise failing slate tiles can absorb moisture and cause rot. If there is evidence of moisture damage in the attic, the slate is probably too old to salvage.
Check for active leaks in the attic and in living areas. Look for water damage in first- or second-floor rooms as well.
Go outside and examine the roof covering the interior areas where you noticed signs of leakage. Use binoculars or stand on a ladder to see the roof clearly. Look for damage to the metal flashings, or the valleys and gutters near the leaks, keeping in mind that the visible leak may not be right under the damage. If these materials are causing the leaks, you can repair them instead of replacing the roof.
Stand across the street from your house and look at the roof through a pair of binoculars. Locate the cracked, slipping or missing tiles. Determine whether they are all in one area or scattered across the entire roof. If the damage is all in one area, the problem might be with the other building materials rather than the slate, and you might be able to salvage many of the tiles. Even if the tiles are not usable, you don’t need to replace the whole roof if only one area is damaged.
Check fallen slates for firmness by tapping on them with your knuckles. If they make a resonant sound, they are in good condition; if they make a dull sound, they are not. If the fallen tiles are in good condition, the fault is probably in the metal fasteners that attach the tiles to the roof, rather than in the slate. If the metal is corroded but the tiles are still sound, you can repair the roof.
Estimate what percentage of tiles are failing in each section of the roof. Replace any section where 20 percent or more of the tiles are damaged. If damaged tiles are found all over the roof, the tiles are probably too old to salvage, and it’s time to replace the roof. If more than 10 percent of the total surface of the roof is damaged, The Slate Roofing Company might be unable to replace the failing tiles without breaking the ones beside them. This can make it more cost-effective to replace all the tiles. Ask The Slate Roofing Company for our opinion.