Metal roof coating, repair & retrofit in Houston

A coating goes over the roof that is already there, so three things decide whether it is worth keeping.

Rust on the surface, not through it. Surface rust is not a reason to replace a metal roof. It gets scraped or wire-brushed and primed. A panel rusted through gets that section cut out and replaced first.

Panels tight to the framing. Loose or buckled panels get refastened or replaced first, because a coating will not hold a loose panel down.

Leaks at the details: fasteners, laps, the ridge, trim, gutters and curbs. That is where metal roofs usually give up first, and what a restoration is built to fix.

Standing seam and R-panel get looked at differently. R-panel is screwed through the face of the panel, so every fastener is a hole with a washer on it. Standing seam is held by hidden clips, so its trouble is usually at the seams, ridge, panel ends and curbs.

We walk every section, check fasteners and laps by hand, and look at the panels and framing from inside the building. We check whether the rust is on the surface or through, and whether the roof has been coated before, and with what.

Manufacturers publish both acrylic and silicone systems over metal; Karnak, for one, lists both. Which one goes on your roof depends on its slope, how it drains, what is already on it, and how much the details move.

Acrylic is bright, white and easy to recoat, and suits a metal roof that sheds water. It will not sit under water that stays after the rain. Silicone holds up under standing water, which helps on a very low-slope roof with a few low spots. The catch lasts the life of the roof: about the only thing that bonds well to silicone is more silicone.

A metal roof gets the manufacturer's published system for metal, named in the proposal.

Metal roof recoating is the lighter job, for a coating that has chalked or worn thin but is still stuck to the roof. It gets cleaned, peeling spots come off, worn details get repaired, and a new coat goes over the top. Acrylic generally takes more acrylic. Silicone takes only silicone, and silicone over old acrylic generally needs the manufacturer's primer and an adhesion test.

Metal roof sealing usually means sealant over the screw heads and laps. On an otherwise sound roof that can be the right repair. Sealant over a loose fastener leaves a loose fastener, though, so the fasteners come first.

Not sure whether your roof was ever coated, or with what? A commercial roof inspection gives you a dated record of what is up there.

A metal roof retrofit builds a new TPO or PVC roof over the existing metal, and the metal never comes off. When the panels and the framing under them are still sound, we generally prefer a metal retrofit to tearing off sound steel for new panels. The building is never opened to the weather.

A coating gives the roof you have a new surface. A retrofit changes what kind of roof the building has. It fits leaks across the whole roof rather than at the details, a building that needs more insulation, or an owner who wants a welded membrane roof.

The build goes in layers. Insulation cut to the panel profile fills the gaps between the ribs so the top comes out flat, with more insulation over it where needed. Cover board is fastened down over that, and the TPO or PVC membrane goes on top with its seams welded with hot air. Membrane manufacturers such as Duro-Last publish metal retrofit systems along these lines.

Curbs, pipes and rooftop units get flashed into the new membrane, and edges and gutters get new metal. The added height can mean raising curbs and units.

A retrofit can go on a metal roof of any slope. On a steep metal roof whose panels are not too far gone, though, we would generally coat it instead. A retrofit adds weight and is fastened through the old panels into the purlins. Any doubt that the framing can hold both goes to a structural engineer before anyone prices the roof.

Membrane manufacturers generally issue system warranties only on roofs installed by contractors they have approved. More on the membrane itself is on our TPO roofing page.

A coating over the wrong roof is an expensive delay. Three things take a metal roof out of the running.

Rust-through across the roof, not in a few places. A few rusted-through sections get replaced and the roof gets coated. Holes all over the roof mean there is not enough sound metal left to coat.

Panels that are loose, buckled or pulling away from the framing across large areas.

Framing that is rusting, sagging or has moved. Rusted purlins go to a structural engineer, not under a coating.

If the roof is past coating, we tell you that, with the photos to show why. What is left is a retrofit if the structure is sound, or replacement if it is not.

On new panels, Wade gives the answer he gives on any roof: “I wouldn’t start with replacement. First we need to find out where the water is getting in, what shape the roof is actually in, and whether the leaks are isolated or the whole system is failing. If the roof can be repaired and bought more time, I’ll tell you that. If replacement is the smart move, I’ll show you why and give you the numbers.”