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What You Need to Know About Inspecting Slate Roofs

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You can tell the slate tiles on this roof are in rough shape, but all slate damage isn’t this easy to see.

As a home inspector, you likely inspect lots of roofs covered in asphalt shingles. But what about slate roofs? You may not come across many, but if you do, this type of roof covering must be treated differently during inspection.

Although slate roofs can be beautiful, they are significantly more expensive than asphalt shingles, so you don’t see nearly as many homes with slate roofing tiles. The fact that slate tiles can last for 200 years doesn’t sway many homeowners.

But they don’t last forever, and checking on their condition is an important part of a home inspection.

Don’t Walk on a Slate Roof

It isn’t necessary to walk on a roof to inspect it properly. In the case of a slate roof, it’s dangerous for two reasons: one, you could fall off and get injured or worse, and two, slate tiles break easily underfoot.

However, examining the tiles from the ground isn’t sufficient either. You can’t see what shape they’re in from there. Inspecting the tiles from a ladder leaned against the eaves should be adequate.

From this vantage point, you can identify tiles that are suffering from delamination, or separation of the layers. You can diagnose this problem by sight, but you must physically examine a few of the slates to see if the problem is only on the surface or if it has penetrated throughout the tile. Surface delamination is not an immediate cause for concern.

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This repairman is accessing the roof with staging, so he doesn’t damage the tiles by walking on them.

Check for Damaged Tiles

Look for any broken or crumbling tiles when inspecting a slate roof. Tiles can crack if they are struck by an object like a falling branch, and missing or cracked tiles can be replaced.

Inspectapedia says that if more than 25 percent of the tiles are damaged, it’s not worth it to try to repair the roof, and replacement should be considered instead.

Another problem that plagues slate roofs is failing flashing. Most flashing is made of metal, and it won’t last as long as the slate. It can last longer if painted regularly, but walking on the roof to paint the flashing can cause the tiles to break.

If the flashing on a slate roof is damaged, but the tiles are still good, slate roof professionals can replace the flashing safely and restore the roof’s integrity.

Keep an Eye Out for Substandard Repairs

Some sources say it’s important to identify the type of slate on the roof you’re inspecting. For help with this task, go to Slate Roof Central.

Regardless of the type of slate used, the method for fastening slate shingles to a roof is the same — with nails. Straphangers should not be used to fasten replacement tiles. It isn’t necessary, and it’s ugly.

If, while inspecting a slate roof, you see it has been repaired with tar, make a note of it because this is not a good method of repairing leaks on a slate roof. It doesn’t last, and it ruins the tiles.

To learn more about inspecting roofs, check out our home inspection course. We include two sections on roofing that cover terms, materials, shingle types, defects, and the inspection process. Get a demo of the course to check out for free.

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