Should I coat or replace a commercial roof?
Coat it if the existing roof can be repaired to watertight, the deck is solid and the insulation underneath is mostly dry. Replace it if moisture has spread through the insulation, the deck is corroded or rotten, or the membrane has failed across large areas. A moisture survey tells the two apart, and it matters because a coating sealed over wet insulation traps the water inside the roof.
A coating renews the surface and cannot repair what is underneath it
A roof coating is a liquid that cures into a single membrane with no seams over the existing roof. It goes over metal, modified bitumen, built-up roofs and most single-ply membranes, with a primer matched to the surface. The common types are acrylic, silicone and polyurethane, and each handles sun, standing water and foot traffic a little differently.
On a sound roof, a coating does a lot. It seals seams and fasteners, reflects heat off the building, and stops the slow breakdown of a membrane that has been baking in Texas sun for years. In some cases a replacement is not necessary at all, and a high-grade poly coating can be a simple, cost-effective way to strengthen the existing roof and add years to its life.
What a coating cannot do is fix the structure below it. It will not dry out wet insulation, stiffen a corroded metal deck, or reattach a membrane that has pulled loose from the building. Whatever condition the roof is in when it gets coated is the condition it stays in underneath.
Wet insulation is the line between a coating and a new roof
Water that gets through a commercial roof often does not drip into the building right away. It soaks into the insulation board and spreads sideways, where it can sit for years. Wet insulation loses most of its insulating value, adds weight to the structure, and rusts or rots the deck it sits on.
That is why coating guidance calls for a moisture survey before anything goes on. An infrared scan, usually done in the evening as the roof gives off the day's heat, shows wet areas as warm patches. Core cuts through the roof confirm what the scan found and show what the layers are made of.
Wet sections have to be cut out and replaced with dry insulation before a coating goes over them. When the wet areas are small and scattered, that is routine prep. When moisture runs across a large share of the roof, the cost of replacing all that insulation starts to look like the cost of a new roof, and replacement becomes the better spend.
Standing water matters too. Acrylic coatings generally are not made to sit under ponding water, while silicone tolerates it better. A roof that holds water after rain may need drainage fixed, or a different coating chosen, before the decision is final.
A coating costs less up front and keeps the building open
Coating an existing roof avoids the tear-off, the disposal and most of the new material, so it usually costs substantially less than a replacement. The building below stays in use while the work goes on, with no open deck over inventory, equipment or tenants.
Manufacturers commonly tie the length of a coating system's warranty to how thick it is applied, with terms often ranging from ten to twenty years. When the coating wears thin, it can usually be cleaned and recoated over the top, so the roof underneath can keep going for another cycle without being torn off.
The savings only hold if the roof was a good candidate in the first place. A coating over a failing roof buys a few quiet years and then a replacement anyway, with the cost of the coating added on top.
Replacement is the better spend once a roof has run out of repairs
The signs point the same way on most roofs that need replacing: widespread wet insulation, soft spots or rust through the deck, a membrane shrinking and pulling at the edges, and blisters or splits across the open field of the roof. Building codes also stop a new roof covering from going over two existing roofs, so a building that has already been re-covered once usually has to come down to the deck.
Hail changes the math as well. If a storm has damaged the roof, check whether the building's insurance covers it before paying for a coating, since a covered loss may pay toward a replacement.
Power House installs metal, asphalt, mechanically attached, fully adhered and Rhino Bond roof systems as well as metal roof coatings, and we can repair, restore or replace a commercial roof depending on its condition, your goals and your budget. Call (817) 720-6465 for a free estimate on your commercial roof.
Related questions
How long does a commercial roof coating last?
It depends on the coating type, how thick it is applied and the condition of the roof beneath it. Manufacturer warranties on coating systems commonly run from ten to twenty years, and a worn coating can usually be cleaned and recoated when the time comes.
Can you coat a roof that is already leaking?
Usually, once the leaks are found and repaired and any wet insulation around them is replaced. A coating goes over a roof that has been made watertight, and it will not seal an active leak by itself.
Can a metal roof be coated?
Yes, and metal is one of the most commonly coated roofs. Rust is treated and primed and the seams and fasteners are sealed before the coating goes on across the whole surface.
