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Inspecting Metal Roof Coverings

When I first started performing home inspections, most metal roof coverings I encountered were on barns. That is not the case today. Metal roof coverings are becoming very popular. We will be seeing more and more of these roof coverings for many reasons. There are many different types and styles of metal roof coverings available. A rib style or standing seam was most popular, however there are many different styles and types available. Many metal shingles look like dimensional or asphalt tab shingles. Some look like cedar, slate, or even clay tile.

So why are they gaining popularity?

Most metal roof coverings can be installed over an existing roof covering, however some manufacturers recommend purlins are installed first, so there is normally no need for a tear off. Therefore, there may not be that much of a price difference (current prices range between $700 and $1200 per square installed) . Most metal roof coverings come with a true 30 to 50 year or even a  lifetime transferable warranty. It won’t crack, burn, curl or rot. So why bother inspecting it! Only kidding, there are many things that a home inspector should know and examine when conducting a home inspection.

First the inspector should look at the finish. There should not be any rust or damage. If there are dents or damage, especially near a seam, check closely for a leak. It is not recommended that a home inspector walk a roof that has a metal covering, however some metal roof manufacturers state that their roof coverings, if installed properly are walkable. I would ensure it is safe before walking one. Closely examine any area that has been cut or trimmed, like edges or around penetrations. It is recommended that snips are used when it is cut. This will ensure the coating is rolled under. Using a more aggressive blade or saw may take the coating off and rust may form.  Flash points are another area where we may see a problem. Most of the metal roof manufacturers supply factory fabricated flashing components. You can usually tell because the color will match the roof and they fit secure. If the flashing is a different color than the roof covering, or it appears that the installer ‘fabricated’ it himself, pay close attention, not only to the flashing, but all the areas. If the wrong flashing material is used galvanic corrosion may occur. Seeing tar would be a clear indication of a problem.

One of the biggest problems encountered with metal roof coverings is condensation.

As home inspectors, we know the importance of ventilation on a conventional roof covering, it is just as, if not more important under a metal roof covering. Another way to control condensation is to add foil faced blanket polyethylene insulation. This type of insulation seals up small gaps and blocks up to 97% of radiant heat. This will ensure the heat is reflected back and help control condensation. If you see water drops or stains on the ceiling, it may be a condensation problem.

Some types of spray foam insulation may react with the metal and cause it to degrade. Some manufacturers recommend fiberglass insulation when metal roof coverings are installed. The underside of the metal covering may be difficult to inspect from the attic space, because it is installed over plywood. It is recommended that metal roofing is installed over decking, however there must be a vapor barrier over the plywood, but again we will probably not be able to see it.

What about grounding?

It is recommended that a metal roof (and siding for that matter) be grounded if the house is within 200 feet of a main electric transmission right of way, the house  has more than 2000 square feet of metal surface and is closer than 150 feet from a main electric transmission wire, or the building is storing flammable materials and within 250 feet of a main transmission wire.

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