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 > What type of insulation?

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myredracer

Langley B.C.

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Posted: 06/24/19 09:37am Link  |  Quote  |  Print  |  Notify Moderator

colliehauler wrote:

pianotuna wrote:

Think about how a vapor barrier is installed in a house.
That was the point of me asking. They use unfaced and I wondered about using faced and humidity build up in a closed roof, no attic to vent.
This is the problem. RVs have the vapor barrier/retarder on the wrong side of a wall or ceiling compared to buildings. If using batt insulation in a ceiling in a building, you require a gap or space for air movement and it needs to be vented to remove moisture, whether it's a vaulted ceiling or has an attic.

When batt insulation absorbs moisture, the R-value drops. Not good. And in cold weather you can have a high humidity level if you don't take measures to remove moisture-laden air.

The very best insulation job you could do is spray foam. It doesn't require an air gap to the underside of a roof deck. It encapsulates everything and leaves no un-insulated cavities. Costly for a small area like in an RV unless you could perhaps tow it to a job site somewhere where they're doing a spray foam job. If you lucked out and found someone, I'd do the underside of the floor too.

If it were me, I'd look at using closed cell rigid foam. Glue it to the underside of the roof deck and build it up in layers using PL400. Fill any voids with spray foam in a can. You'll end up with a very well insulated ceiling that way. I bought a ton of rigid foam for our garage floor at a building recycling place for a fraction of the new cost. Just don't use open cell rigid foam.

For spray foam or rigid foam, you'd of course need the ceiling down.

RV manufacturers do a lousy job of insulation ceilings. Ours has voids all over, isn't very thick and is compressed all over. The open cell foam they use in walls is also a poor choice as moisture migrates right through it to the exterior fiberglass where it will condense.


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B.O. Plenty

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Posted: 06/24/19 10:43am Link  |  Quote  |  Print  |  Notify Moderator

It takes only seconds to peel the paper off of the insulation to make it unfaced. If that's what you want to use it is not an issue.
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colliehauler

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Posted: 06/24/19 12:00pm Link  |  Quote  |  Print  |  Notify Moderator

Purchased Dow blue foam 1.5 inches thick, will fit between the 2x2 or I should say 1.5x1.5 rafters.

myredracer

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Posted: 06/24/19 12:31pm Link  |  Quote  |  Print  |  Notify Moderator

colliehauler wrote:

Purchased Dow blue foam 1.5 inches thick, will fit between the 2x2 or I should say 1.5x1.5 rafters.
Some photos of the install might be nice. [emoticon]

StirCrazy

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Posted: 06/25/19 06:39am Link  |  Quote  |  Print  |  Notify Moderator

colliehauler wrote:

StirCrazy wrote:

2" foam would give you a much better R value than the stuff that was in there.

Steve
The problem is the roof is 6 inches in the middle to zero inches at the sides. I like the idea of foam especially since moisture should not effect it. Will probably use foam and maybe some regular insulation on the side of the roof.


that's not a real problem, could do spray foam as some one mentioned, the bonus is you could phone a company and travel to where they are doing a job and get them to spray it, would be much much cheaper than if you got them to come to the trailer and set up just for your job.

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Slownsy

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Posted: 06/25/19 06:22pm Link  |  Quote  |  Print  |  Notify Moderator

The problem with anything solid or spray foam is if you ever has to run a new wire or fix a water leak.
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opnspaces

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Posted: 06/25/19 06:47pm Link  |  Quote  |  Print  |  Notify Moderator

If the roof is open and the area tapers from 1 inch on the edges to 6 inch in the middle; I would buy 6 inch thick insulation and just pull it apart by hand as necessary to taper it down to 1 inch. You could also just smash the 6 inch stuff down at the edges, but I think it insulates better if it's not compressed. As far as the facing, as mentioned above just peel the facing off. Although it's much cheaper to buy it unfaced.


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