EPDM, TPO And Fiberglass Age Differently

Arguments about which RV roof material is best are not much use to somebody who already owns one. The coach came with what it came with and nobody is changing materials until the roof is due anyway. The question that does matter is how much notice the material gives before it starts costing money, because notice is what separates a reseal from a replacement.

That gap is large. Roof recoat and reseal work runs $750 to $4,500. Membrane replacement runs $3,500 to $18,000. Whether an owner lands in the first band or the second is very often a function of how many months of warning the material provided and whether the owner was looking at the right thing during those months. The three common materials differ enormously on both counts.

None of what follows is about identifying which roof you have. If that is genuinely unclear, it gets settled in five minutes with the coach in front of somebody, and it is the first thing established on any roof job. What follows assumes you know, and deals with what happens next.

EPDM is the most communicative of the three. It chalks, and it chalks for years, shedding a white surface layer that runs down the sidewalls after rain and alarms owners who have not been told it is normal. Then it gradually loses suppleness. Then fine cracking appears at radii, at the roof edge and where the sheet rises onto a flange. Then the flange areas start to crack in earnest. Every one of those stages is visible from a ladder.

So EPDM is forgiving in one narrow sense. By the time it is genuinely dangerous, it has been signalling for a couple of seasons, and an owner who looks twice a year cannot miss all of it. Its weakness is the opposite failure: the chalking that looks worst is the stage with the most life left, so owners spend money early on roofs that had years in them.

That cuts against us in a way worth admitting. Owners arrive convinced a chalking roof needs coating, and sometimes we say the roof does not need it yet and they buy it anyway. We write it as maintenance rather than repair, which it is, and it does no harm. It also was not necessary this year, and the honest version of that sentence belongs on the estimate.

TPO is a thermoplastic and it behaves nothing like EPDM as it ages. It does not chalk. It stays bright and reasonably clean for a long time, and its surface tells an observer almost nothing about its condition. An owner reading a TPO roof by appearance will conclude it is close to new right up until the day it leaks, and will be reading it correctly, because the field of the sheet often is close to new.

Where TPO ages is at the joints. Seams on TPO are heat welded rather than glued, and a weld is a fusion of two sheets whose edges have been through everything the roof has been through. Flange perimeters are the other location. When it goes, it goes comparatively abruptly, because a weld either holds or it has separated and there is very little middle ground to observe.

Two practical consequences follow. On TPO, the inspection is the seams and the flange perimeters and essentially nothing else, so the twenty minutes goes in a different place than it would on EPDM. And a repair needs the same welding capability the original seam had, since tape laid over a separated weld is a covering rather than a joint.

A one piece fiberglass roof is a moulded laminate, gelcoat over glass and resin, and it ages by oxidising and dulling. Owners read dulling as cosmetic, which for a long while it is. Meanwhile stress accumulates at a short list of fixed points: the front cap transition, the corners of an air conditioner opening, a ladder mount, the feet of a roof rack or a solar array. Nothing about that accumulation is visible.

The failure is a crack, and a crack in a laminate is not a hole in a skin. Water tracks into the laminate through it and separates the gelcoat from the substrate for some distance in every direction, so the affected area is always larger than the visible line. The repair is grind, layup and refinish rather than a bead of sealant, at $210 per hour for structural and refinish labour.

The blunt summary is that a fiberglass roof looks its best right up to the point where it is expensive. There is no chalking stage to warn you and no seam to watch. What there is instead is a set of stress points that can be checked by sounding rather than by looking, which is a habit nobody develops on their own.

The interval stays the same on all three, twice a year, and there is nothing material specific about that. What changes is where the attention goes, and an owner checking a TPO roof the way they would check an EPDM one is looking hard at the part of the roof that will not tell them anything.

• On EPDM, suppleness and the beads in that order, and treat chalk as information rather than as a problem
• On TPO, every welded seam and every flange perimeter, since the field of the sheet is not where it fails
• On fiberglass, the fixed stress points, sounded with a plastic tap hammer rather than examined by eye
• On any of the three, whether standing water sits anywhere at all after a wash
• On all three, the interior ceiling corners and cabinet tops on the same day, from inside, with a light

Fiberglass is sold as the upgrade and in most respects it earns that. It is walkable, it looks better for longer, it does not chalk down the sidewalls, and it does not need the constant bead attention a rubber roof does. Owners who paid for it are usually pleased with it, and reasonably so. It is also, of the three, the material that gives the least warning and produces the most expensive repair when the warning finally arrives.

Nobody should choose a coach on its roof material. There are a dozen things about a coach that matter more and the roof will be resealed or replaced at some point regardless. But everybody storing a coach outdoors in Orange County should know which of the three they have, because the thing you are meant to be watching is different in each case, and watching the wrong thing carefully is indistinguishable from not watching at all.