Butyl and mastic flashing sweeps residential solar mounting market 2024 Trends in Solar

There’s been a shift recently in the residential mounting sector, with manufacturers prioritizing smaller profile mounts that install over shingles rather than the traditional metal flashing sheets installed under roof coverings. These top-mounted attachments tend to reduce the materials carried to a roof and the number of steps in a solar installation. Previously, there were different flashing methods with each model, some built-in and others using self-applied sealants to waterproof roof penetrations.

Within this segment of residential solar mounting, more manufacturers are opting for pre-installed adhesives, many of them applying a peel-and-stick butyl or similar sticky mastic to the mounting surface of their attachments.

Butyl is a synthetic rubber that was invented in 1937 that can seal and adhere surfaces. Since its creation, butyl has been used in a range of industries and applications, from lining pools to reducing vibrations in engines. The material can be chemically altered to work in different environments, including on residential roofs.

In the last few years, several major residential solar mounting manufacturers have adopted a butyl or similar flashing method. SnapNrack recently debuted its AnchorFoot and DeckAnchor mounts with butyl flashing. EcoFasten is using a combination of butyl and foam on its ClickFit and RockIt top mounts to adhere to the contours of residential roof surfaces. Unirac has a line of roof attachments for mounting and running conduit that uses butyl. K2 Systems now uses a proprietary butyl on its solar roof attachments called EverSeal. Then IronRidge uses a mastic adhesive paired with foam on its Halo UltraGrip top mount that functions similarly to a peel-and-stick butyl attachment.

Despite this recent trend toward this adhesive, butyl has been present in residential solar mounting for nearly 30 years. Roof Tech, the American subsidiary of Japanese PV mounting manufacturer Yanegiken, has used a proprietary butyl called AlphaSeal on its solar attachments since it started making them in 1994.

Additionally, Roof Tech was early to produce solar mounts that are rail-less, attach to the roof deck and install over the shingle. Milton Nogueira, senior business development manager at Roof Tech, said this is common practice for solar mounting in Japan, a country that regularly experiences earthquakes, tropical depressions and generally more moisture than the United States.

The company trusts its butyl flashing enough to put a 25-year warranty on the system. Roof Tech’s AlphaSeal butyl has been rated to perform in up to 180-mph winds and temperatures as low as 40°F. Prior to developing its own, even competitor K2 Systems partnered with Roof Tech to use its butyl on K2 mounts.

“Our flexible flashing lasts much longer and is malleable for longer, and the malleability of the product is what really shows us longevity, because anytime it gets warm, it can make sure that all the voids — if there are any — are filled,” said Kenneth Clem, regional sales manager, Roof Tech. “Whenever you go on top of a roof and you see caulking that’s hard [and] has physical cracks in it, that means a caulking has failed. Our product lasts incrementally much longer than what any caulking does. We’ve showed that over our roughly 30 years of experience.”

Solar mounts using butyl or mastic for flashing generally seal penetrations as a bolt or screw is driven through the adhesive plane and into the roof surface. This lets installers skip the step of applying caulking themselves, and they don’t need to pry up shingles and slide metal flashing plates underneath. This limits the room for installation error.

“[Our product] takes the liability off of the [installation] company because it’s pre-installed with our flashing on the product,” Clem said. “That was the number one thing whenever I was a contractor that I loved about it.”

It’s unclear whether butyl is a passing fad or a longstanding flashing option for the larger residential solar mounting market. But it will remain Roof Tech’s adhesive of choice.

This story is part of SPW’s 2024 Trends in Solar. Read all of this year’s trends here.