Home>Discussions>INSULATION & HVAC>UNDERBELLY: Mobile Home Nightmare!
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aicram62
UNDERBELLY: Mobile Home Nightmare!

First let me give much props to people who install tv, internet phones etc. because I don't know how you figured out where anything belongs.

Under a trailer is a big rubberish plastic sheet called the vapor barrier. and under that is a leaf pile of pink insulation.

My HVAC has not worked in over 5 years. Cats have moved into one side of the lining (double wide mobile home) I moved into the house brand new in 1999 but I know nothing about these things. I have replaced the water heater once 4 years ago but it appears that it is full of rust, because we just had a pipe snap, and when we tried to drain the heater, nothing would come out.

A friend repaired the pipe but recommended we start replacing these pipes because they are all brittle. I would like to use this PEX stuff I've passed over while researching my main question; which is : CAN I USE SOMETHING OTHER THAN THE PLASTIC WATER VAPOR SHEET ON THE UNDERBELLY?

I am very frustrated with going under the house and not being able to see what's what. i would like to take some Owen Corning like insulation tiles or maybe some batt with kraft paper and put them against the floor board. Then I would like to put fiberglass duct wrap around the ducts. Then I would like to put pre-slit foam tubes around all of the pipes. I want to see what is what when I'm under the house. How does that sound?

Re: UNDERBELLY: Mobile Home Nightmare!

i think i am agree with you, right

sissy
Re: UNDERBELLY: Mobile Home Nightmare!

Double wides have the insulation and barrier put into and onto the joists .Best thing to do is put in new plumbing with the new flexable piping for water lines first and take down the old stuff and put up roxul rock wool .It may be more expensive than regular insulation but it does not get damp bugs and rodents don't like it ,it is fire proof and moisture proof .Do you have a permanent foundation and is it vented or unvented .Roxul rock wool stays in place where you put it .Is the crawl space under the house damp

Mastercarpentry
Re: UNDERBELLY: Mobile Home Nightmare!

You've got several issues with mobile homes not encountered in the usual home-repair field. First is the frame, which projects below the insulated area and which interferes with supply piping that must cross it. Following the original routing where it crosses the frame is the easiest way. Bend the PEX wherever possible instead of using fittings but don't kink it. You can insulate it like you mentioned. You can get the original style of covering for the bottom but like anything else made for trailers it ain't cheap. I usually cover up with heavy poly- black or clear will do. The biggest problem is that the covering was originally installed before the frame was attached so you'll have nothing to attach the edges to at the frame once it's cut away. My usual is to leave as much if the original intact as I can for that reason. At least leave say 6" or 8"intact on both sides of each frame rail. They do sell a special tape made for patching that stuff- again not cheap but it works better than anything else for the job. You can also install 1X4 furring beside the frame and attach the covering to that. Let it lap over the frame rails, caulk under that, and use PT lumber. You'll have similar problems at both ends too. You're not going to be able to insulate the ducts like you think- they are a thin sheet-metal box directly under the flooring so you can only see 3 sides of them. And they don't need insulating separately- the floor insulation covers them. What they do need is sealing- apply mastic to every joint in the 3 sides you can access- leaks on top you're stuck with. If you try to drop the ducts to seal that they'll likely fall apart and not be reusable. Fiberglass is fine for insulation here till it gets wet, and you're going to find a lot of that- I ain't yet seen a trailer with all dry insulation after a few years, the gray PB piping and connections are crap that leaks soon after applying water pressure. Glad you're doing a full PEX job, that's the best way to go. Get physical with the drain piping while it's open- pull and twist and try to get the joints apart. If it's black ABS and even one joint fails replace it all- the person fitting the pipe went cheap on glue to make his boss happy so all the joints now become suspect. White PVC is usually OK but I do the same test for it. If it's going to fail I want it to fail while it's open and I'm under there, not later after I sew it all back up.

While I appreciate you wanting to "do this right", it's a trailer and you simply can't unless you take the whole thing apart and start over. When they make these things each new piece goes over the last and you can't do it again the same way after that next piece is put in place. Just do the best you can with what's there and make every effort to keep water out- it will kill a trailer in short order, especially the floors- and make sure that any leaking water cannot collect underneath in the covering. I intentionally poke lots of pen-knife slits in that cover under every wet area and under where pipes run so that if there is ever a leak you can see it and so any water that gets in has a way out and you can see where the leak is. It somewhat defeats the air-seal but with small slits (about 3/8", just poke in and pull out) that ain't much and they tend to stay closed until water hits them. There's not much you can do under a trailer to improve things other than with the plumbing and it's not going to last long enough to make it feasible to re-engineer it all to make it better. It is not a house, it is not built like a house, and it can't be approached like a house when it comes to repairs and improvements because of the way they are built. I know because I work on many of these and I'm currently working on yet another one wishing I wasn't, but it pays well so I take the bad with the good and keep my main customer happy in the process too :cool:

Good luck- you're gonna need it with a trailer!
Phil

keith3267
Re: UNDERBELLY: Mobile Home Nightmare!

Pex cannot be exposed to sunlight once installed. UV radiation will degrade it in a year or two. All water supply pipes must be above the floor insulation if you live in an area that gets temperatures below 32 degrees. If you live in souther Florida or Southern California near the coast, you could run the water lines under the insulation, but anywhere else, no way.

You could remove the fiberglass and the rubber only if you do the following. Insulate the rim joist, that is the joist going around the perimeter of the foundation. Use 2 to 4" think foam or roxul and seal it against outside air. Then do your plumbing but keep it up in the joist cavities as close to the floor as you can. Drill any holes with the smallest drill that will pass the pipes and keep them in the center of the joist.

Then you can use insulating panels called SIPS, for structural insulated panels. They will have foam between OSB boards. Attach these to the bottom side of the joists. An alternative would be to attach 1" foam panels to the bottoms of the joists and then cover those with 3/8" or thicker plywood or OSB. I would use screws so that they can be removed for future maintenance.

Cindy
Re: UNDERBELLY: Mobile Home Nightmare!

We live in a 1979 double wide and vapor barrier is completely gone.  Floors have bowed, sunk and developed holes.  We are repairing one room at a time as the problems happen but the home is constructed on steel joists, not wood.  The sub floor is glued to these joists.  When replacing the sub floor, should be replace vapor barrier (glueing to the steel) then glue sub floor onto the joists or could we simply place the new plywood floor on top of old subfloor?  Would this prevent future bowing/sinking of old subfloor in areas where this has not begun?  Help!

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