Mounting Small Panels on Shingle vs Metal Roofs

By Solar Panel Kits · September 12, 2026

Mounting a small solar panel on a roof involves two distinct challenges: attaching the bracket securely to the roof structure, and weatherproofing the attachment point so it never leaks. The approach depends entirely on your roofing material. Asphalt shingles require penetrating fasteners with proper flashing. Standing seam metal roofs allow non-penetrating clamps that grip the seam. Both methods are well-proven when done correctly.

Shingle Roof Mounting

The standard method for mounting on asphalt shingles uses a lag bolt driven into a rafter, sealed with a purpose-built flashing plate that slides under the shingle course above the bolt. The process starts from inside the attic: locate a rafter in the target area and mark its position. Transfer the mark to the roof surface by measuring from a reference point or drilling a small pilot hole from inside.

On the roof, lift the shingle course above the target location and slide the flashing plate underneath so that it covers the bolt hole. The flashing plate has a raised boot around the bolt penetration that sheds water. Apply a bead of roofing sealant under the flashing plate before sliding it into place, and another bead around the bolt penetration after driving the lag bolt. The shingle course above lies flat over the top edge of the flashing, creating a shingled-over waterproof seal.

Use stainless steel or hot-dip galvanized lag bolts, minimum 5/16 inch diameter and long enough to penetrate at least 2 inches into the rafter after passing through the roofing, sheathing, and bracket. Pre-drill the rafter with a bit slightly smaller than the lag bolt shank to prevent splitting. Torque the bolt snug but do not over-tighten, which can crack the flashing plate or strip the rafter.

For small panels (under 100 watts), two mounting points are usually sufficient. Place them at least 16 inches apart for stability and align them with two different rafters. Larger panels need four mounting points, one at each corner of the panel frame.

Standing Seam Metal Roof Mounting

Standing seam metal roofs have raised seams running vertically from ridge to eave. Non-penetrating clamps grip these seams and provide a secure mounting point without any holes in the roof surface. This is the simplest and most waterproof mounting method available.

The clamp consists of two jaws that sandwich the standing seam, tightened by a set screw or bolt. A stud or threaded rod extends upward from the clamp to accept the panel mounting bracket. Slide the clamp onto the seam, position it, and tighten the set screw to the manufacturer's torque specification. Over-tightening can deform the seam or damage the paint finish, creating a corrosion point.

Clamp width must match the seam profile. Standing seams come in different widths and shapes (snap-lock, mechanical lock, nail-strip), and not all clamps fit all seam types. Measure your seam width and height before ordering clamps. Most clamp manufacturers offer sizing guides or measurement tools.

Tile, Slate, and Wood Shake Roofs

These roofing materials are fragile and require specialized mounting approaches. Tile hooks slip under individual tiles and hook onto the batten underneath. Slate roofs need custom brackets that replace individual slates. Wood shake roofs use lag bolts similar to asphalt shingle installations but with different flashing profiles. For all three, the risk of breaking roofing material during installation is high, so experience or professional installation is recommended. Small panels under 50 watts can sometimes be mounted on wall brackets or pole mounts adjacent to the building to avoid roof penetration entirely.

Waterproofing Details

Every roof penetration is a potential leak point. The waterproofing hierarchy for lag bolt mounts on shingle roofs is: flashing plate under the upper shingle course, sealant under and over the flashing, and sealant around the bolt penetration. Use roofing-specific sealant (polyurethane or butyl-based), not silicone caulk, which does not adhere well to asphalt shingles and becomes brittle over time. Inspect sealant annually and re-apply as needed. Even a well-sealed penetration can leak eventually if the sealant degrades, so annual inspection is the insurance policy.

Standing seam clamps are inherently waterproof since they do not penetrate the roof surface. The only leak risk is if the clamp is over-tightened and deforms the seam enough to break the surface coating, creating a corrosion point that eventually perforates. Torque specifications exist for a reason.

Wind Load and Structural Considerations

A panel mounted on a roof catches wind, and the force is transferred through the mounting hardware into the roof structure. Small panels under 100 watts present modest wind loads: roughly 30–50 pounds of force at 60 mph. This is well within the capacity of two properly driven lag bolts or four standing seam clamps. For larger panels or high-wind areas, consult the mounting hardware's wind load rating and ensure it exceeds local wind speed requirements. Most building codes require mounting systems to withstand at least the local design wind speed, which ranges from 85 mph in calm inland areas to 150+ mph in coastal hurricane zones.

Routing Cables

After mounting the panel, route the cable from the panel's junction box down to the battery or charge controller location. On roofs, run the cable along the panel frame, down a mounting rail or conduit, and through a weatherproofed roof or wall penetration. Use a cable entry gland or a drip loop at the penetration point to prevent water from following the cable inside. Secure the cable with UV-resistant clips or ties at regular intervals so it does not flap in the wind. Avoid running cables across foot-traffic areas of the roof where they can be stepped on and damaged.

Thermal Expansion and Seasonal Movement

Roofing materials expand and contract with temperature changes, and mounting brackets must accommodate this movement without loosening or creating stress cracks around the fastener holes. Shingle roofs expand modestly, and the lag bolt plus flashing system absorbs this movement well. Standing seam metal roofs expand significantly along their length as temperatures swing from winter lows to summer highs. Clamps must grip the seam firmly enough to resist wind uplift but with enough compliance to allow the seam to slide through the clamp slightly as the roof panel expands and contracts. Over-tightening clamps on a metal roof can buckle the panel or cause the clamp to cut through the seam coating, initiating corrosion.