How Thick Is The Roof?

Madrona · 04-10-2016, 04:20 PM

Does any know how thick the roof is on a typical class A motorhome? I want to mount something but not sure how long the screws should be. Also, is the roof solid or do I need to find joists?

I asked a similar question but didn't get any pertinent answers so thought I would keep it simple.

This is for my 2003 Itasca Horizon.

Thanks for any help!

Phil

afrohman · 04-10-2016, 04:28 PM

They can vary depending on the motorhome. Easiest way to see the thickness is to measure the depth of one of your roof vents. I attached a new AC distribution box made of oak without finding any trusses to attach but its not very heavy.
Hope that helps
Adam

powercat_ras · 04-10-2016, 04:32 PM

Take the plastic shroud off the bathroom fan and look there, then you will know exactly what it is for your specific RV. It is likely about 2".

For "mounting something" the only solid structure you will be hitting is the 3/16 " roof below that you are just screwing thru soft foam so there's really no advantage to screws that penetrate longer than about 1" into the roof .

Chances are your 'bago has Fiberglass over plywood roof construction so it can help to use adhesive under whatever you are mounting to help hold whatever you are mounting. It also helps reduce chance of water penetration into the screw hole. I have used 3M outdoor mounting tape when mounting air horns and two side butyl tape under solar panel "z" brackets. Finally you want to put Dicor self leveling lap sealant over the top of the fasteners to make very sure you don't get any water into the roof where you have created new penetrations for screws.

Mr_D · 04-10-2016, 04:34 PM

Quote:

Originally Posted by afrohman

They can vary depending on the motorhome. Easiest way to see the thickness is to measure the depth of one of your roof vents. I attached a new AC distribution box made of oak without finding any trusses to attach but its not very heavy.
Hope that helps
Adam

The OP is asking about the actual thickness of the roofing and backing, not the depth between the roof and inside ceiling.

OP: remove a vent surround inside and you can see the roof material and decking it's attached to.

LeeOts · 04-10-2016, 06:07 PM

On our previous WGO View 24J as well as our current WGO Vista 30W, we mounted solar panels on the roof with 3M VHB tape. I check it from time to time but have never seen any signs it's coming loose. Google "3M VHB" for a bunch of YouTube videos showing its strength.

Here's one from when it was still called "Scotch VHB."

Madrona · 04-11-2016, 12:28 PM

Thanks, All, for your suggestions and info. I hadn't thought of the vent box idea and I like it, so I will remove one before I proceed.

ga traveler · 04-11-2016, 12:39 PM

Just remember, you will find the vent "boxed in". The 2x or 1x will not be under all the roof.

Cooperhawk · 04-11-2016, 12:41 PM

Winnebago uses extruded steel as joist, not wood. The vent will tell you the thickness but a magnet might help find the joist.

Madrona · 04-11-2016, 02:35 PM

Quote:

Originally Posted by ga traveler

Just remember, you will find the vent "boxed in". The 2x or 1x will not be under all the roof.

That's why I was trying to find out how thick the sheeting (plywood?) is. I probably didn't make that clear when I asked how thick the roof is. There must be some kind of sheeting on top of the trusses. I wonder how thick that is and if it will hold a screw of say, 1" length.

Arch Hoagland · 04-11-2016, 02:40 PM

Drill a hole through the roof and see for yourself exactly what the thickness is and then seal the hole with caulking.

I suspect it will hold a 1" screw just fine but the only way to know is to see it yourself.

What is it that your are going to mount?

tderonne · 04-11-2016, 03:55 PM

The fiberglass skin on top is very thin, maybe 0.040". Under that is 1/8" luan / plywood. Then about 3" of foam. Then a layer of wood and the finish ceiling inside.

The "joists" are effectively nonexistent, they are flat steel, placed vertically. If you look real close at the Superstructure pictures in the brochures you can see that. The strength lies in the fact that it is all bonded together.

Folks have used sheet metal screws to screw into the fiberglass and luan layers, but many also used adhesive. I chose to go overkill and through bolted my satellite dish. I located the bolts in under an interior light, and in the AC ducts.

Madrona · 04-21-2016, 06:06 PM

So, I was installing a new satellite dish, that's why I needed to know the roof thickness. In the end, I just drilled the four holes, needed. I didn't check, first. Here is what I encountered:

I used 1 1/2" long, #10 sheet metal screws. About a 1/4" of length was taken up by the base of the dish, so into the roof/ceiling by 1 1/4". The first two screws went directly into sheet metal as soon as I penetrated the outer skin. The other two screws went into nothing. I had applied sealant into and around the holes and set the base directly in place. Drove in the screws until almost tight, squirted some more sealant under the heads and finished driving them home. I tried to move the dish and it seemed stable. Now that the sealant has cured, I'm sure the unit will not move.

Thanks to everyone for their ideas and suggestions!