What Makes a Metal Installation Last
Nearly every metal roof problem we are called to in Sacramento is an installation problem, not a product problem. Four details account for most of them.
High-temperature underlayment
A metal roof deck gets hot. Standard asphalt felt degrades under it, and degraded underlayment is the only thing between your sheathing and the next leak at a flashing.
A high-temperature synthetic or self-adhered underlayment rated for metal is not an upgrade. It is the specification.
Allow the panels to move
A long steel panel at 105°F is measurably longer than at 40°F, and Sacramento delivers that swing routinely. Standing seam clips are designed to let the panel slide; eave, ridge and penetration details must not pin it.
Pin a panel at both ends and it oil-cans, distorts at the seams, and works its fasteners. This is the most common metal defect we see locally and it is entirely avoidable.
Keep the metals compatible
- Copper in contact with aluminium or bare steel corrodes the other metal — fasteners and flashings must be compatible
- Copper runoff onto a galvanised or aluminium surface below causes the same problem at a distance
- Fasteners should match the panel system, not simply be whatever is on the truck
- Pressure-treated lumber in contact with metal requires appropriate separation and compatible fasteners
Ventilate the attic
Metal radiates heat away at night and can run cooler than the surrounding air, so condensation on the underside of the deck is a real possibility in an under-ventilated attic. Intake at the eaves as well as exhaust at the ridge is the answer.
A ridge vent with blocked soffit intake does almost nothing, and that is an extremely common condition on Sacramento homes.
Ask how many they did last year
Metal is roughly 4.6% of Sacramento County re-roof permits, which means most local roofers install very few. Ask any bidder how many standing seam or stone-coated roofs they completed in the past year and ask to see two of them.
Competence with composition does not transfer. This is sheet metal work.
Common questions
What underlayment goes under a metal roof?
A high-temperature rated synthetic or self-adhered membrane. Standard asphalt felt degrades under the heat a metal deck reaches, and once it has, the flashings are the only thing left.
Why is my metal roof wavy?
Usually oil-canning from thermal movement that was not allowed for, or from a deck that was not flat to begin with. Matte finishes and heavier gauges hide it; proper clip detailing prevents it.