The short answer
A coating works when the membrane is intact, the insulation underneath is dry and the problems are surface level. It fails when there is trapped moisture, because you seal water inside and accelerate deck damage. A moisture survey answers which situation you are in.
Side by side
| Factor | Coating | Full replacement |
|---|---|---|
| Relative cost | Roughly a third or less | Full cost |
| Added service life | Typically 10 to 15 years | 20 to 30 years |
| Disruption | Low, usually no tear-off | High, building affected |
| Wet insulation | Makes it worse | Removed and replaced |
| Warranty | Coating manufacturer only | Full system warranty |
| Prerequisite | Dry, sound substrate | None |
Choose Coating if
- The membrane is intact and the roof is not saturated
- A moisture survey comes back clean
- You need to defer capital spend and extend service life
- Seams and flashing can be repaired before coating
- The roof has adequate drainage already
Choose Full replacement if
- A moisture survey finds wet insulation
- Seams are failing widely rather than in a few places
- The roof ponds water that does not drain within 48 hours
- The membrane is at or past its service life
- You want a full system warranty
What this looks like in the Hill Country
In San Antonio the reflectivity argument helps a coating case, since a white coating on an aging dark membrane cuts cooling load noticeably. But reflectivity does not fix wet insulation. Get the moisture survey before anyone prices a coating, because a coating over saturated insulation is money spent making the eventual tear-off more expensive.
