I am new to the business.  Went to a residence that has a mobile home that has an addition and metal roof.  This roof is about 8ft above the original mobile home roof at the ridge and extends passed the home to form a covered porch.  This roof is raining water from condensation on the old roof and ruining the new soffit not to mention all the other problems the water will cause.  The metal roof is uninsulated but has a white membrane of some kind (not Tyvek).  It has a vent on both ends 1ft x 2ft and some small openings on one side of the lower roof just after the porch roof.  The original roof has about 4" of fiberglass insulation.  The roof cavity is open and there is about 2 to 3ft  feet of clearance with no other obstructions.The addition has about a 1:12 roof that has fiberglass  insulation with a plastic covering that has been stuffed into the cavity filling it.  The water scares me for liability reasons but would like to help if I could.  Do I insulate the underside of the metal roof?  Do I blow in insulation into the old roof.  Do I foam the top of the existing? Do I walk away? Heat is propane wall units and fireplace.  Location Seattle

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LOL, par for the course with some of these fixes for mobile homes - you are talking about a second roof added above the first one / not attached at all? The easiest fix is to install a system like one uses under the deck to drain water away - insulating it wont help. As for the addition part, you didn't really describe it all - pictures do help - so I cant even begin to guess on that

As for old roofs, insulating, etc... it all depends & as I said there isn't enough info. For more on Mobile Homes & tricks used - http://blog.sls-construction.com/2010/weatherization-program-modula...

I can't understand the situation very well, but you noted "propane wall units and fireplace".  I will bet that they are all unvented; burning propane produces a GREAT amount of water vapor into the living space, as well as the products of combustion(!!).  If that's the case, I would have them read the lots of negative information about unvented gas appliances, and if they don't change them, first for their own personal safety, second to stop the water production, then run away. 

A quote from one source I found: "Any amount of propane that you burn in a space heater will produce approximately 163 percent as much water."  Then there's the carbon monoxide(!!), oxides of nitrogen, etc.  all of which the living and breathing should not be living with.

Walk away. To be blunt, in my opinion, if you are asking these questions on this project, you should be starting with less complicated jobs.

Manufactured homes are not the same as stick built, although there are similarities. The bathroom vent fans are typically vented through the roof, which would be dumping warm moist air into the new roof cavity. I have found some manufactured homes to be rather tight, leading to higher Relative Humidity. Usually there is a furnace that is also vented through the roof, which may not be flashed properly or kept away from combustibles with the new roof. Did they properly extend any of these roof penetrations (flue pipe, stack vents, etc)?

Did they cut holes in the original roof? There are different ways to fix this, but the added metal roof will make it more challenging to resolve. Dense-pack cellulose is a possible solution, if done properly. Spray foam is not a solution, unless you are going to rip off the entire roof. 

Pictures are needed.... but honestly,  I'd walk away.  I live in Seattle area.  

If for some reason you need to stay with it and work on it...  you need lots of pictures - for your protection long term, and you need to test-in and test-out.

Adding any insulation without understanding the problem is going to cost you big time.

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