Mounting Systems and Roof Integrity: Structure In, Water Out

Rails can be shimmed within the maker’s allowances and let you land on framing that does not line up with the ideal layout. Every splice and bolt is a long-term reliability question; aluminium grows on hot days and shrinks on cold ones, and splices must follow the maker’s rules. Rails are also part of the bonding path.

Rail-less bonding comes from many small interfaces (washers, bonding clamps, listed jumpers), so “metal touches metal” is not enough. Ballasted arrays sit on pads with blocks sized for wind by roof zone; the roof membrane is a fragile, expensive, continuous sheet that a dragged tray or a loose shaving can slice.

PV dead load is usually light; the bigger drivers are wind uplift, sliding and snow, repeated for decades. A flush array changes wind flow and can concentrate uplift; modules change how snow drifts and sheds. A roof that held snow for years may still need evaluation because the geometry has changed.

A lag off the rafter centre can split it; an overdriven lag strips and looks seated with no strength left; rotten wood will not hold a fastener; a truss is a designed system that is never cut in the field without an engineered repair. Correct pilot holes, embedment and torque are what make the engineering assumptions true.

The attic is one of the best truth sources: framing size, spacing (confirmed, not assumed), notches, alterations, staining, mould and repairs. Engineering letters and racking packages assume certain roof conditions; your job in the field is to recognise when conditions are within those expectations and when they are not.

Ask the questions before committing: framing type and spacing, condition of decking and framing, water damage, wind and snow requirements, whether the attachment schedule matches the roof zones, and anomalies like vaulted ceilings or additions. If you cannot answer them, you do not know whether the roof can carry the system.

Lift shingles gently, separating the adhesive strip without tearing the mat; in the cold, shingles turn brittle, so slow down. Order matters: flashing set first and then fought through by the lag deforms or tears it; a lag cranked down too hard dishes the flashing and makes a spot where water pools.

Follow the flashing’s listing on nails: random nails are random leak points. If a pilot reveals no rafter, stop, patch that test hole the proper way, and relocate; smearing sealant on top of a puncture can still fail when water runs under the shingle.

Tiles shed water by overlap, and the underlayment beneath is often the real waterproof layer; use the attachment made for that tile profile. Standing seam clamps avoid penetrations, but overtightening deforms the seam. On through-fastened metal, bonded-washer fasteners go where the panel maker says.

On membrane roofs, protect the sheet, keep drains and scuppers flowing, and never cluster ballast; point loads crush insulation and cause ponding. Keep cables supported off the roofing and out of drainage paths, and leave room for future service so the next technician is not forced onto fragile areas.