Heritage Restoration, Inc.

Solar panels on slate roofs

We are visiting Newport for the Jazz Festival and were thrilled to read your column..

We live in wash DC, and our home has a Vermont slate roof. Is this a suitable roof for a solar installation in your opinion?

Betty, Washington D.C.

Hope you loved the Jazz fest and Newport!  Fort Adams is an amazing venue and even a cooler place to explore and tour.
Slate and solar are fine together, yet the challenge is finding a solar installer that either knows slate, or has a slate roofing contractor that can properly install it. Typically the solar panels are on a rack and rail system, consisting of metal tubes that support the solar panels.  When the rack and rail system is installed on an asphalt roof, most installers use a roofing cement to seal the screw penetrations.  I have seen a few flashing details, although they seem to rely more on the roofing cement than the flashing.

Slate is one of the most cost effective roofs period. Slate is extremely reliable and durable when done right, where a properly cared for slate roof can last over 100 years.  Yet an unknowing or unskilled contractor that messes with slate can quickly ruin a great investment.  I have seen roofing cement repairs on slate that prevent the slate from properly moving, bleed, cause the slate to break or melt away from moisture being trapped, and just does not work.  Roofing cement is a 5 year product; pretty much useless on a slate roof.  And then a contractor can do even more damage by walking all over the slate, causing the slate to break, leak and cost you even more money for repairs.  Properly fixing a slate roof is really straight forward if you know what you are doing.

So that being said, there are proper ways to install solar on a slate roof.  But finding a solar installer to do it right may take some time.  I would strongly suggest getting a solar installer that has proven success in installing solar on slate, or they work with a slate roofer to properly prep for the rack and rail.  You will pay a bit more for the install, but it will still be worth it with the PACE financing options and other Washington DC specific and federal solar incentives.  I would highly suggest a copper flashing system, where the copper laps the slate in a similar manner to the existing slate.  Also that the location of the rack and rail pressure points are not at all in any way touching or sitting on the slate.  The important thing to remember is that the solar panels have a life of about 25 years, and the slate over 100.  So be mindful that that solar panels are only temporary relative to the life span of the roof.

Thank you for visiting Rhode Island and going solar!

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