Insulating under mobile home


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Old 02-08-11, 05:26 PM
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Insulating under mobile home

We've got an older double-wide mobile home. There used to be fiberglass insulation under the entire house, installed against the bottom of the sub-floor and covered by a tarp-like material.

The insulation has fallen off under most of the house, due to two reasons:

1) At some time in the past there was a plumbing leak in both of the bathrooms. This wet the fiberglass, weighing it down to the point where the tarp covering split and the fiberglass fell to the ground.

2) The AC ducting is run under the house. Condensation has formed on the ducting, wetting the fiberglass and causing the same problem as the plumbing leaks.

I'd like to re-insulate under the house - the floor gets cold, even with rugs and carpeting. I'd like to use a closed-cell foam insulation, but it's out of the price range yet.

Any suggestions on another type of insulation that would work in this situation? Or any work-arounds for using fiberglass?
 
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Old 02-09-11, 04:15 AM
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I have my guys repairing plumbing under one today, and will, after it dries out, replace the insulation and barrier. My method may or may not work in your situation, so here goes. If the tarping is in good enough shape (only split) you may be able to install new insulation holding it up with 2x2's spanned across the I beams about every 2' or so, then tape the tarp up as you go with Tyvek tape or an equivalent. I am going to try that to see if I can pull the tarp together enough. We had to split it ourselves to let the river run out. If you haven't thought of a solution, I'll let you know how this turns out. Maybe you can get'r done before me. Good luck
 
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Old 02-09-11, 04:39 AM
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If the underside of your MH is like most I've worked on, there isn't enough of the belly wrap left to salvage What I've done is replace the missing insulation with batts and then use tar paper in place of the original wrap. 1x2s or even strips of plywood work well to keep the tar paper in place.

On single wides the duct work always runs inside of a joist cavity but I'm not sure how it does in a double wide. If the duct work isn't insulated, there is a special insulation you can put on it but I don't know much about it.
 
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Old 02-09-11, 01:23 PM
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The belly wrap is shot in most places, patching it won't work. I'd thought of replacing it with one of the mid-priced plastic tarps, the kind that's made of woven plastic strips, not a solid sheet of plastic.

The local "Home Improvement" radio guy has said that fiberglass insulation is prone to holding moisture from condensation next to the flooring which would cause the flooring to rot. I'm not so sure about that since the manufacturer felt that fiberglass is acceptable.

Where might I chase down the ducting insulation? Would it be available at one of the big box stores or should I look to an HVAC installer/supplier?

chandler
It'll be a while before I can work on this, so any info on how your job goes would be appreciated.
 
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Old 02-09-11, 02:55 PM
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"Where might I chase down the ducting insulation? Would it be available at one of the big box stores or should I look to an HVAC installer/supplier?"

I don't know if a big box would have it or not but a HVAC supply house would.
 
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Old 02-09-11, 04:17 PM
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Thanks. I'll make some calls tomorrow.
 
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Old 02-09-11, 04:58 PM
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Cliff: I've got to cut it all out and start over. My guys went under to repair what the customer thought was one broken pipe turned out to be the entire network of cpvc shattered like glass. Gotta replace about 200 lf of the stuff. THEN comes the insulation replacement. I, like you, thought about using the tarps to span across and keep the insulation in place along with Marksr's idea of the spanner lumber, too.
Customer lives in Floriduh and turned the water off to the trailer. Didn't bother to open a faucet and drain the lines, even after I put a drain valve in for them to use. They set their thermostat on 40 degrees and took off for warmer climes. They were almost out of propane. Gas guys came to fill tank and didn't check the pilot light to the furnace. Went into the house today. I set the thermostat to 50 degrees. It was 31 inside 29 outside. No heat. No wonder.
I'll let you know how it goes with the insulation and tarps. Maybe by the time I get finished by the time you get ready!!
 
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Old 02-09-11, 05:38 PM
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That's good for business but - ouch! The client's got to be a bit unhappy.

Seems as if the tar paper would be more air tight, not sure if that would be a good or bad thing.
 
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Old 02-10-11, 04:50 AM
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I have only been under a few and never tried to do any of the work you are describing, but access for future service comes to mind. Along with that is the thought of a canvas with some zippers installed so sections could be removed when needed. Probably out of the question price wise, but a nice mfg option if they would offer it.

Bud
 
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Old 02-10-11, 12:03 PM
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I haven't checked out every place under the house, but what the manufacturer did under the shower was to build a wooden box directly below the drain. They built & insulated the box (w/foam insulation) and screwed a lid to the box, then ran the fiberglass insulation and covering against the sides of the box. Sure made cleaning the P trap for the shower a lot easier.

Building a few boxes around the other potential problem areas are in the plans.
 
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Old 02-13-11, 04:00 PM
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Still pondering this, and was wondering about using the rigid foam insulation sold in 4' x 8' sheets. I see there being two possible ways to use it:

1) Since I'd be working by myself, cut it into 4' squares. Screw it to the bottom of the floor joists. I'd use strips of ply or 1" x material to screw through and hold the insulation in place. This method would leave gaps around the support columns under the house; figure to possibly fill those gaps with some of the spray-in expanding foam. I'm thinking this method would also provide insulation for the plumbing, where the second method would require working around the piping.

2) Cut the insulation to fit between the joists. Screw 2" x 2" blocks to the inside, or across the edges, of the joists to hold the insulation in place. With this method the insulation would be free-floating, not attached directly to the joists.

Both methods would allow for a dead air space between the insulation and the bottom of the sub-floor.

To further insulate, I was considering cutting the foam board into strips sized to fit inside the steel channel used for the frame.

I haven't researched the R values of fiberglass vs foam board, but installing multiple thicknesses of the foam board would be possible if needed.

Would either of these methods be better than the other? Or is there a problem with using the foam board I'm not aware of (yet)?
 
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Old 02-13-11, 05:17 PM
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Not sure on the foam. It may work. What I am seeing in my situation is I may go back with insulation between the joists and staple the tarps up like we discussed earlier, rather than trying to run the insulation lengthwise across the joisting as it came from the factory. Now, that left an air space all across the trailer, which may have been good as long as the barrier was intact. But you have to figure, after the insulation was placed on the jig in the factory and the house sat on the metal frame, it squished the insulation to a zero insulation factor at those points, so not sure my method wouldn't be better, since I would not compress any insulation. I'll post results.
 
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Old 02-28-11, 09:12 AM
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Cliff, we finished this monster. had to replace almost all the piping under the MH. We excised the insulation from the affected areas. I noted the pipes that ran parallel to the floor joists were up in the cavity, but the runs perpendicular were below, so there was a logistical problem with the insulation. I could not just put insulation up in the joist cavity. We had to put it running perpendicular to the joists, stapling where possible, then cutting tarps to cover the bottom, and staple it to the joists and rims to keep vermin, etc down.
Fun job.
 
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Old 03-01-11, 09:32 AM
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Sounds like quite a job. Because of what you found with the plumbing, think I'll go with the fiberglass insulation. Should be simpler/easier to work with than the rigid foam.

Which tarps did you use?
 
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Old 03-01-11, 04:36 PM
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I just bought some of the 6x10 or so blue tarps from big orange, stretched it to contain the tacked up insulation, then stapled it with narrow crown staples everywhere there was wood, cutting the excess off afterwards.
 
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Old 03-01-11, 07:09 PM
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Thank you Sir. Thought those might have been the tarps, but wanted to make sure.
 
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Old 12-18-11, 07:21 PM
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Suggest having a look at buildingscience.com for understanding on whether you might get rot and where you want vapor barrier vs. vapor retarder. This will depend on your climate and where the dew point is in the insulation. If your climate varies between hot and cold it may be best to have a vapor retarder both sides, no vapor barrier, but I'm no expert and refer you to the site.

I see you've got AC and it's forming condensation, seems clear you'll want more insulation on the ducting and vapor barrier wrapping that (installed when it's dry).

One thing I've done for holding rigid foam in place is to cut hardboard into about 3" squares and drill a center hole (in stacks of them for speed).
 
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Old 12-19-11, 08:41 PM
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Thanks, I'll check it out.
 
 

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