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Old 02-09-2020, 10:47 AM   #1
Fourbtgait
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Roof Insulation

New to us Passport. When I dropped the inner trim ring of the center skylight to find a hot lead for adding a vent fan, I noticed jest a 2-3” blanket Insulation. The roof is wood bow truss’s.
Has anyone ever added blown in insulation using house attic blower on a long wand?
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Old 02-09-2020, 11:07 AM   #2
chuckster57
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Welcome to the forum!!

I would think that air gap is designed to be there and I personally would leave it as is.
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Old 02-09-2020, 11:37 AM   #3
Fourbtgait
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What do you base that on?
In residential house construction you vent the roof having a minimum 1” air gap. If the roof is sealed, no vents, then the insulation is required to be against underside of roof deck.
Now before you say its not a house, are you sure the variables also don’t apply?
To much heat in an attic, or rv closed roof, can delaminate the plywood.
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Old 02-09-2020, 11:47 AM   #4
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I base it on 9 years of working on RVs and seeing the same gap on every unit I’ve worked on. Even the bigger fifth wheels that have a vented attic.
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Old 02-09-2020, 11:49 AM   #5
Fourbtgait
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Where are the vents for the attic?
Never seen those. Picture?
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Old 02-09-2020, 11:54 AM   #6
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I have seen them on Grand Design Solitude units for one. Can’t say I’ve seen them on the “lower cost” units.

I have no scientific basis for my opinion and as such it is just that. You can do what you want, I said and stand by my original post- I wouldn’t do it.
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Old 02-09-2020, 01:19 PM   #7
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The 2018 Passport brochure advertises R-11 roof insulation.

If you compare to "house insulation", roll batting designed for 2x4 walls (3.5" thick) is R-13. Typically, RV companies "maximize R- values" by adding the insulation value of the OSB decking, TPO sheeting, luan ceiling panels together to get the "best advertising boasts" as possible. So, I'd suspect that the insulation in your roof is probably 2.5" - 3" at best.

Can you blow in insulation? I'd ask how you're going to access the areas to get "blown in insulation" evenly distributed and whether adding it would be worth the effort when you've still got R-7 walls, single pane windows and "holes everywhere that leak heat/cool air from the cabin.....

As Chuck said, you can pretty much "do anything that fits" to an RV, the question is whether it's wasted effort or a means to improve some aspect of the trailer. "super-insulating the ceiling" likely falls in the "wasted effort" category when you consider the rest of the "energy inefficiency" that's left after all the effort..... YMMV
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Old 02-11-2020, 07:14 PM   #8
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R, since the trailer is new to you, use it for a year to see how it performs. Then give your idea a try.

If it works, great. If it doesnt, no big. Nothing ventured, nothing gained. Chick and John posted the potential down sides. To my knowledge, no o e else on the forum has done this mod.
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Old 02-11-2020, 08:57 PM   #9
Fourbtgait
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Quote:
Originally Posted by ctbruce View Post
R, since the trailer is new to you, use it for a year to see how it performs. Then give your idea a try.

If it works, great. If it doesnt, no big. Nothing ventured, nothing gained. Chick and John posted the potential down sides. To my knowledge, no o e else on the forum has done this mod.
It is not the first travel trailer I have owned in my life. Just one of many including p/u camper, 5th wheels, living quarter gooseneck, Benroy I built along with a cargo trailer fully outfitted with heat, running h/c water. I was simply curious if any one had for the fact pointed out before that the true R value is below what manufactures state. We boondock, don’t use generators.
I also realize as pointed out what is the cost vs gain factor. The same applies to doing insulation, window, etc upgrades in houses. I am a project manager building houses. Which brings up the point of the comment of vented roofs in trailers.
As pointed out, “low cost” trailers like I own probably don’t vent roofs. True, I learned something there. Namely there is such a thing as roof vents for trailers, found them with google.
Problem with them is, are you really venting the roof? Without edge venting you have to increase the number of square inches of vent per square foot of roof area if you truly want to lower the trapped heat and moisture vapor in the roof system. But that square inch of venting would need increased because the screen used in vents technically reduces that vents capacity. To technical? Not really. One square foot of vent covered with 1/4” hardware cloth is only .75 square foot now. Decrease screen size, it drops even more.

Enough rambling on my part, take care, happy camping.
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Old 02-12-2020, 02:44 AM   #10
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Quote:
Originally Posted by Fourbtgait View Post
I was simply curious if any one had for the fact pointed out before that the true R value is below what manufactures state.
As pointed out, “low cost” trailers like I own probably don’t vent roofs. True, I learned something there. Namely there is such a thing as roof vents for trailers, found them with google.
Problem with them is, are you really venting the roof? Without edge venting you have to increase the number of square inches of vent per square foot of roof area if you truly want to lower the trapped heat and moisture vapor in the roof system. But that square inch of venting would need increased because the screen used in vents technically reduces that vents capacity. To technical? Not really. One square foot of vent covered with 1/4” hardware cloth is only .75 square foot now. Decrease screen size, it drops even more.

Few have pointed out that these manufacturers exaggerate just about everything about a RV. I've never seen once insulation being anywhere as dense as house insulation. And the foam board used is rated like blue board even though is the cheap styrofoam. Add some reflectix to that overated stuffing and you get R40+ as they say. R18 for the non dense stuff then another R20+ for something actually rated at 1.1.


The venting, well I guess people misunderstand why vents are
used , how they work to release excess hot air, lessen/prevent ice jams etc. And you have to have a lower inlet to go with the higher outlet, OOPS, doesn't have one.
Go ahead and stuff the attic of the RV, it'll only be better. If I could easily get into mine, it wasn't new, I'd do the same thing because that's where and RV biggest loss area is.
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