You've stumbled upon a common debate in the solar installation world! L-feet with mastic directly screwed into shingles are definitely used, but whether they're becoming common and whether they're a good solution is a point of contention. Here's a breakdown

What you're seeing:
L-feet with Mastic

These are aluminum L-shaped brackets that attach the solar racking to the roof. The mastic (a sticky, sealant material) is pre-applied to the bottom. The installation involves finding the rafter underneath the shingles and screwing the L-foot directly into the rafter, relying on the mastic to create a watertight seal.

Arguments FOR this method



Speed and Cost

This is the primary driver. These installations are significantly faster and cheaper than traditional flashing methods. Time is money for solar installers.

Reduced Shingle Disturbance

Advocates claim less disturbance to surrounding shingles compared to methods that require lifting or cutting shingles.

Arguments AGAINST this method (and why many installers avoid it)



Long-Term Watertightness

This is the BIGGEST concern. Mastic can dry out, crack, and degrade over time, especially with UV exposure and temperature fluctuations. Shingles expand and contract with temperature changes. The L-foot is rigidly attached to the rafter. This differential movement can stress the mastic seal, leading to leaks. The screw holes themselves are potential entry points for water. While the screw itself might have a rubber washer, that's another potential point of failure. Wind-driven rain is extremely good at finding weaknesses in a roof.

Roof Warranty Issues

Many roofing manufacturers explicitly void warranties if you penetrate the shingles without using approved flashing methods. The solar contractor might offer their own warranty, but that's only as good as the solar company's solvency. If they go out of business in 5 years and your roof leaks, you're out of luck.

Lack of Best Practices/Code Compliance

While some jurisdictions might allow this method (or simply not have specific regulations against it), it generally goes against best practices for roof penetration sealing.

Aesthetics

Some argue that exposed L-feet are less aesthetically pleasing.

What most reputable solar installers use for shingle roofs

The gold standard is

flashing-based mounting systems. These come in a few common variations: Standard Flashing with L-Foot

This involves using a metal flashing plate (often aluminum or galvanized steel) that slips under the surrounding shingles. An L-foot is then attached to the flashing. The flashing diverts water away from the penetration point.

Installation Process

1. Locate the rafter.
2. Gently lift the shingles above where the L-foot will be.3. Slide the flashing plate under the shingles (overlapping the course below).
4. Attach the flashing to the rafter with screws.5. Attach the L-foot to the flashing.
6. Seal around the flashing with appropriate sealant.7. Carefully lay the shingles back down, ensuring they are properly sealed.

"Comp" or "Composition" Mounts

These are pre-fabricated mounts that combine flashing and the L-foot into a single unit. They're often designed to be easier and faster to install than traditional flashing, while still providing superior waterproofing compared to direct-to-shingle methods. Examples include Quick Mount PV and IronRidge FlashFoot. Installation process will vary by the specific mount, but generally involves similar steps of locating the rafter, integrating the flashing under the shingles, attaching the mount, and sealing appropriately.

Tile Replacement Mounts

For tile roofs, these replace existing tiles with a tile-shaped flashing and mounting point. This is the only way to really achieve a waterproof seal on tile roofs.

What I think (and what I recommend)

I would strongly advise against the direct-to-shingle method with mastic. While it might save money upfront, the risk of leaks and potential roof damage down the road is simply not worth it. A leaking roof can cause far more damage than the cost savings of a cheaper solar installation.

Recommendations


Always prioritize flashing-based mounting systems. They are the proven method for creating a long-lasting, watertight seal.2. Research and choose a reputable solar installer. A good installer will prioritize quality and long-term reliability over cutting corners. Ask about their mounting methods and warranty.3. Check with your roofing manufacturer. Confirm that the chosen mounting method won't void your roof warranty.4. Verify local codes and regulations. Ensure the installation complies with all applicable building codes.In summary, while the direct-to-shingle with mastic method might seem tempting due to its speed and cost, it's a gamble that often doesn't pay off in the long run. Protect your roof and your investment by insisting on a properly flashed mounting system. Flag for review