Rubber roof replacement on a fifth wheel

[Cholmes100]

I am sure this has been beat to death but a search really didn't get the info I needed.  My 34 ft 5th wheel roof is due to be replaced from age and damage. I have a new piece of rubber or EPDM and it is actually a commercial piece so thicker than the RV stuff you buy.  I know this is a big job so I want only to do it once and my question is: I know the roof sheathing is 3/8 in plywood and then the rubber.  I would like to have another barrier over that sheathing such as Ice/Water shield. That way if there ever is an issue there still is a layer of protection. So can the rubber be safely laid directly over the Ice/Water shield?  Anybody ever done that? I'm guessing it would be fine unless the two materials react with one another. The other option is a layer of 1/4 inch pressure treated plywood over the Ice/Water shield then the rubber but that means considerably more work, cost, issue with vents and so on. The current plywood has an aluminum radius over the long edges and that was stapled on and the staples work up and poke holes in the rubber so the ice shield should solve that as well otherwise they all will have to be pulled. Any ideas, suggestions? 

 

[donn]

I think you will be adding a lot of weight 13 feet in the air for little to no benefit.

 

[Kevin Means]

The "rubber" roofs on RVs are actually very effectve water barriers if the edges and cut-outs for things like AC units, antennas and vents are sealed properly. It's not unusual to get 20 years out of them with minimal care. If I were going to replace it, I might look into applying a good sealant to the substrate (as long as it didn't repel the glue) but I can't see much benefit in adding another layer of substrate to the roof. JMO.

Kev

 

[Cholmes100]

I think you will be adding a lot of weight 13 feet in the air for little to no benefit.

Weight is not a concern, Reality is it is a couple hundred lbs so a weekend beer supply.

 

[Cholmes100]

well if you tear the rubber and let's face it, it tears very easily, then there is a water shield under that. Same concept as a shingled roof. Shingles are an effective water barrier but I have never seen a roof shingled without tarpaper or Ice shield under them.  Same logic

 

[Old_Crow]

Ordinarily the rubber membrane is glued down to the roof.  You'd have to glue your plastic membrane to the roof, then glue the rubber to the plastic membrane.
I can visualize a couple of different ways this could go wrong. 
I also think it's highly probable that anything that impacts the roof hard enough to tear the rubber roof isn't going to magically stop at the plastic membrane, making the whole exercise a waste of time and money.

 

[Gary RV_Wizard]

I see no problem with adding another barrier layer as long as you install it properly, meaning firmly adhered to the layer below, with the EPDM layer then glued onto that. How much value it adds seems doubtful to me, but that's your call.  If there are staples or screws working loose in the substrate, that's a problem ht has to be solved regardless, and I'm not sure that just covering over it is enough.

There is no particular reason to use EPDM for the top layer either - you could install a sturdier material such as TPO or rolled fiberglass sheeting.

 

[CharlesinGA]

The problem is, the adhesive used to install RV rubber roofs is water based and needs fresh wood for the water to go off into so the adhesive will cure. Using the water based adhesive over old roof sheathing that has a previous layer of adhesive from where you pulled the roof off, or if you added an additional layer of a water proof material, would keep the adhesive from properly curing.

I have had people tell me the adhesive will cure, people who worked for RV shops and claimed they did it all the time (installing over the original wood with old adhesive on it), however, I don't think they ever bothered to follow the RV down the road and see the rubber lifting from the roof when the adhesive didn't cure. I talked to Dicor tech support, he told me that the alternatives were, 1) replace all of the roof sheathing with new, or 2) overlay the roof with a very thin Luan plywood applied with construction adhesive and screws or nails/staples. Dicor makes the stuff, they should know what will and what won't work. I took them at their word and stripped all of the roof sheathing (3/8 OSB, no longer manufactured) and re roofed with plywood and screws. While the sheathing was off I sistered the trusses with 3/8 plywood glued to the sides of the trusses and stapled with ? crown staples

Thats my two cents worth.

Charles

 

[Gary RV_Wizard]

Good info, Charles. Obviously the type of adhesive used is a key factor and the requirements for using it are probably overlooked by to many installers. Dicor's "water-based bonding adhesive" might not be suitable if the Ice & Water Shield was underneath.  I can't tell for sure from the Ice & Water specs, but it appears to be asphalt-based. Obviously resistant to moisture penetration.

 

[longhaul]

Always check with the mfg of each product to make sure adhesives....roofing material are all compatible with the other.