Why wood/rubber roofs on 5W's?

We've looked at a lot of new and used 5th wheels (various brands) over the last six months, and viewed a number of videos of manufacturers' construction/production processes. It appears that they all use plywood covered with rubber on their roofs. I'm so used to a virtually worry-free fiberglass roof on our motorhome and on boats with a 'hard top'. Any reason that 5W's don't have fiberglass roofs, especially given the additional care and maintenance required with rubber-covered plywood?

FWIW while touring a dealer's lot recently, the salesman asked if we'd be interested in a "nice" used 5W. This unit had just been traded in, and it was immaculate inside and on the visible outside. I climbed up the ladder to take a peek at the roof. I placed a hand on the roof forward of/adjacent to the ladder and realized that an area approx 15"x15" was "soft". Looking around, I could see an excessive amount of sealant had been applied in that area. Clearly, the owner had a leak, tried to fix it, and eventually decided to trade the 5W before things got worse. We quickly said "no thanks".

Tom, aside from cost and possibly weight savings I wonder if it could be the variety of roof profiles. Whereas Class A's tend to have a relatively similar profile, fivers vary quite a bit. Mine for example is deeply arched full length, plus slopes aft from the axles back. Seemingly a much more complex form to construct from fiberglass.


While I too am not a fan of rubber roofs, because of the arch I like this roof much more than the one on my Dutch Star - it sheds water much better. The Dutch Star (rubber) was very nearly flat, which worried me given the number of caulked openings and seams. Plus the sides of the Dutch Star wrapped up on to the roof creating a moulding joint the full perimeter where the rubber met the fiberglass siding. While this looked clean standing down on the ground it created nearly 100' of worrisome caulk lines up on the flatter part of the roof where I felt it could be much more prone to leaks. In contrast my fiver roof wraps down over the sides perhaps 4". There is of course still a perimeter seam where the roof meets the siding, however this seam is on the vertical side exposing the seam to much less water pressure and opportunity for leaks. (The front cap is an exception where the cap wraps back.) Plus that joint is sealed with a much 'tighter' caulk more similar to silicone. I don't think it's silicone as that's not rubber roof friendly but it's definitely not a Dicor type sealant. Where I have done my minor Dicor touch ups up top, the perimeter seam appears it will be maintenance free for some time. (That reminds me though, I do need to figure out what type of edge sealant was used.)


One thing I don't like about the arched and wrapped roof, I don't like being up there, at all. Given that it's a foot taller than the Dutch Star and with the deep arch and lack of defined edges due to the wrap, I find walking anywhere much outside the centerline to be worrisome. When I recently scrubbed the roof I did it with a stiff deck push broom and was very careful to remain on non-soaped areas. To reach the outer edge I accessed it from the ground and a 10 foot ladder. Wasn't a fun job but don't expect to do it often. I want to apply a treatment (although unnecessary according to the roofing manufacturers) and have procured a mop so I can stand centerline and reach the edges.

You should distinguish between traditional EPDM rubber and TPO, which is technically "rubber" but very much different.  I would have no qualms at all about a TPO roof, e.g Dicor Diflex II or similar.  As far plywood decking (substrate), I don't get the concern. Motorhomes & site-built homes use plywood decking too.  The difference between good ones and cheap ones is the thickness and the quality of the construction.

A 5W such as the Forest River Riverstone has 1/2" decking, a TPO roof membrane, and lots of insulation (that's an example, not a particular brand/model recommendation).

I think the reason they use it is the flexibility of the membrane - it conforms to the angles in a 5W roof whereas fiberglass or aluminum would have to be sectioned and seamed. I rather have one continuous piece that 2-4 sections with intervening seams.

I can see cost and ease of manufacturing, to some degree. Looking at Forest River's manufacturing video shows how quickly they can install plywood and the rubber membrane on the underlying aluminum roof structure. However, it's not clear that it's a 1-piece roof; Looks like it's multiple sheets of plywood with nothing to "seal" the joints; It's all down to the overlying membrane. Meanwhile, there's definitely something about a fiberglass roof, either 1-piece or with with glassed-in seams.

Scott, just curious which type of membrane you have on your Montana HC. The 2019 Montana owners manual talks about both Dicor EPDM and the Alpha Superflex TPO membrane. Haven't seen many references in specs, so how do you tell which one a particular model uses, and what's the advantage of one v the other?

Understand the concern about height; I've always hated heights. But IMHO there's nowt worse than wet fiberglass for the possibility of slipping. Chris used to wash the hard top on our boat (partly because I didn't fit through the hatch and partly because of my fear of heights), but I no longer allow her up there after she fell once. Our Monaco fiberglass roof has two strips of diamond texture for walking along the length of either side of the roof to provide traction, but I'm still not comfortable up there.

Tom said:

Scott, just curious which type of membrane you have on your Montana HC. The 2019 Montana owners manual talks about both Dicor EPDM and the Alpha Superflex TPO membrane. Haven't seen many references in specs, so how do you tell which one a particular model uses, and what's the advantage of one v the other?

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I'm guessing EDPM but just a guess. Don't know, and don't know. I guess I need to find out what I have  :-[

Back2PA said:

I'm guessing EDPM but just a guess. Don't know, and don't know. I guess I need to find out what I have  :-[

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Don't ask me Scott.

I wouldn't know how to tell the difference, but I can categorically say we have neither on the roof of our coach 

Rene T said:

Don't ask me Scott.

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Rene, what kind....... nvr mind 

https://www.youtube.com/watch?v=mEUmZ4-z1Bg

2019 Grand Design roof replacement after original blew off.

TPO EDPM identification: https://www.youtube.com/watch?v=KL5qJw397Rc

lynnmor said:

TPO EDPM identification: https://www.youtube.com/watch?v=KL5qJw397Rc

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Thanks lynnmor

Rene T said:

Don't ask me Scott.

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Tom said:

Scott, just curious which type of membrane you have on your Montana HC.

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EDPM. Now we all know

Now that we know how to tell the difference, and that TPO is the "good" one, we just need to take a staple remover, screwdriver(s) and stepladder with us next time we go to a dealer.

Tom said:

TPO is the "good" one

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I stopped watching the video when it got to the part on how to identify. I have the bad one??  :-\ :-\ :'(


(I didn't have to pull a staple)

[quote author=Back2PA]I have the bad one??[/quote]
Gary made the call in his message. I'm just putting a note in my phone that "the same color both sides is OK". Oh wait, was it the other way around?

FWIW the roofs of used 5Ws I've looked at around SVRR and new/used 5Ws at dealerships were brown/tan and had dimples, not smooth like the ones in the video. Now I'm really confused  ???

I didn't have to pull a staple

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I suppose it depends on whether it was a Monday or Friday coach.

However, it's not clear that it's a 1-piece roof; Looks like it's multiple sheets of plywood with nothing to "seal" the joints; It's all down to the overlying membrane.

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??  No different than a site built house - the plywood decking on those isn't sealed either.  Ditto for a fiberglass roof RV.  I've never seen the plywood substrate sealed at the joints - it's only purpose is to mechanically support the outer membrane/shingles/sheeting.  It's the skin that keeps the water out, not the substrate.

[quote author=Gary RV_Wizard]No different than a site built house ...[/quote]
Huge difference IMHO, and not a good analogy. On our house, and all I've looked at, the 'tar paper' keeps the water out, and it's protected by shakes, shingles, tiles, etc. The same with various park models we've looked at recently, although some had metal as the top protective layer. The "rubber" aka membrane I've seen on 5Ws has nothing to protect it ...
I'd be concerned about causing damage if I walked (or crawled) up there, which is one reason I respectfully didn't climb onto the roofs of 5Ws we've looked at; In each case I told the owner or dealer employee I didn't want to damage anything. In another topic, we were discussing snow removal from roofs of 5Ws by guys using shovels; I can't imagine that they couldn't/wouldn't damage the membrane, whereas they could shovel the fiberglass roof of our coach all day and do little more than scratch or chip it.

It's the skin that keeps the water out, not the substrate.

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That's what I said, so we agree on that:

[quote author=Tom]It's all down to the overlying membrane.[/quote]

Huge difference IMHO, and not a good analogy. On our house, and all I've looked at, the 'tar paper' keeps the water out, and it's protected by shakes, shingles, tiles, etc.

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The tar paper (it's actually felt) is not the waterproof layer, though it does serve as a back-up layer if there is leakage above.  You would be very unhappy if you only had tarpaper on the roof. 

In any case, you won't find seam sealant or tarpaper on the under-layers of any RV roof, whether EPDM, TPO, PVC, fiberglass or aluminum.

Bottom line, there's nothing protecting the EPDM or TPO membrane from damage.

So, back to my original question, (other than manufacturing/cost issues) why do they use this stuff on the roofs of 5Ws? I understand that lots of 5W owners have one or the other. If we decide to go that way, it looks like we'd be storing a 5W in covered storage, away from snow and away from the guys with shovels.

Talking with our 5W-owning WY neighbor on the phone this week, he was quite adamant that he's not letting the shovel guys on his snow covered roof. In addition to possible damage to the membrane, he mentioned my other concern that these guys can and do cause damage to roof vents and skylights.

Meanwhile, he's still not worried about the snow load, but did mention that several 5Ws in our park had roof damage due to heavy snow a couple of years ago. His bottom line was that, if something happens to his 5W, he has insurance.

Motor home chassis and structures doesn't  flex like a trailers frame/sidewalls/roof construction. That constant flexing would create cracks in fiberglass at some point especially as the trailer is dragged over rough terrain.
That flexing is one down side of metal roof material plus shrink and growing (cold and heat) adds stress mainly to sealants around roof fixtures and roof jacks or other screwed down fixtures.

One big down side for fiberglass is cost for repairing vs aluminum or rubber roof material. I had a part time RV/mobilehome repair business some years ago. I specialized in exteriors and structure repairs.
                    Having repaired aluminum/glass and rubber roofs I find rubber roofs are easier and cheaper to maintain. Regardless of roof type its best to do at least a once a year check up there.
My '97 31'  10" roof length with a rubber roof 5er has never leaked. Some of the sealant is OEM.  I've replaced a few spots with self leveling Dicor per their instructions.

Most of our best hi quality trailers out here are and have been wood sidewall/roof construction with a rubber roof material.

[quote author=longhaul]Motor home chassis and structures doesn't  flex like a trailers frame/sidewalls/roof construction. That constant flexing would create cracks in fiberglass at some point especially as the trailer is dragged over rough terrain.[/quote]
Thanks for jumping in, your explanation makes sense. OTOH our fiberglass boat has survived a number of trips down the CA coast and back, sometimes in pretty rough waters. That hull and everything above (and below) the waterline flexed a lot. I understand the relatively high cost of fiberglass and gel coat repairs.

I suppose I'm over-sensitive by the horror stories I've heard/read about "rubber" roofs, and the ease with which the membrane can be punctured or torn. We likely wouldn't know it had been compromised until too late. OTOH our intended use of a 5W would be to leave it on our site for a season, then store it in covered storage at a nearby town for the winter; Relatively benign usage, and very little travel (a few highway miles between our site and the storage facility).

I'm also sensitized by the fact that we lost an entire roof on a previous motorhome. It wasn't a "rubber" roof, but the design was such that leaks all around the perimeter and where vents/skylights penetrated the roof were almost guaranteed. By the time we discovered what had happened, it was too late.