Redoing underbelly on 1973 DW

[andy7726]

Hi everyone, I am going to be redoing the underbelly myself on my 1973 double wide after a furnace company replaces the two tracks with galvanized sheet metal this friday. This is in northern Michigan, so I have to do all this fast as I can at this time in the year. Got a quote of $4200 to redo underbelly and reinsulate with just r-13 from the only ones that do it in this area, yeah just nuts, alot of elderly people live here and thats what they do for them.

Anyhow, right now what is down there is about 3in of insulation stuck to the back of the I am guessing original belly board, this does next to nothing and floors are very cold in winter, it is like cardboard, with a thin black layer on either side about 1/8" thick, no insulation for a good 2 feet out from the rim joists, It is stapled along rim, and to the floor joists, but the staples are a good 6" form each other allowing cold air to get into the belly along the rim in wind, as the wrap hangs alittle between staples. The wrap is fed under all the steal I beams and hangs down with the insulation a good foot from the bottom of the floor joists, I rough measured 5 1/2'' thickness for the floor joists that I could get insulation in, this might be off a bit, it was through a hole.
The furnace tracks sit below the floor joists, so there is a good gap to the floor, cardboard whatever covers about 1/4'' thick under tracks with no insulation.

I plan to tear out old wrap and insulation along both furnace tracks about 6 1/2' wide I beam to I beam for duct install, and at that point there is only about 30in of old on the front and the back of the place to replace and insulate, and another 6 1/2' right in middle of the place, so I am going to get those out too, and will be putting down the 6mil black vapor barrier on the ground once complete and wont get torn, but have now run into two different methods of doing the belly, and have alot of questions.

1. r-19 unfaced held into joist spaces against floor(particle board) with wire, 16x80 "mobile flex" product to be cut and used as wrap, stapled and glued at rim, fed under I beams, stapled at all joists, flex mend tape for any tears during install.

Now, someone told me this way the pipes can freeze? they are copper piping throughout place, most along tracks, did not freeze during last winter without furnace running at all, some guy tells me that is because there was an air pocket under whole place, and air could move? this does not make scene to me as it would be below freezing air. Heat tape is on main supply line about 4 feet just ground to wrap.
The rest I just had 3 space heaters going in living space$$$$$$$ as I had no money for duct, UB replacement last year. I guess the concern here is compressing the pipes with insulation in spots where it is not along the tracks? if so should one leave a gap for the lines above the insulation a few inches in those areas?
I would really prefer to do it this way with insulation between joists, but not if it will cause problems.

2 r-19 or above faced, and glued to same or different wrap, and nothing in joists, this would allow the "gap" between the insulation and joists, floorboards and some air to cycle around, but my floors would be colder.

What type of wrap is best to use, it looks like the flex mend mobile flex bottom board is the only one I can find for sale online, is it the right stuff for what I want to do? would it work with method 2 if needed? (weight support of insulation).

A local guy uses house wrap for all ub replacements, says its the only product that will breath and not trap moisture, and to use that in place of mobile flex, with the unfaced r-19 in floor joists?

Will the fiberglass r-19 be the best option if done in joists, I got about 5 1/2''-6'' thickness for joists, don't want to compress, but r-13 is too low. If it "hung" down a few inches from the floor joists would that be a problem if it was not compressed and held up well? I had planned r-30 for this. or is another type of insulation that mold can not grow on a better option for ~6in?

What would be a good insulation to place under the new metal furnace tracks? can I use r-13?


This is all the questions in my head for now,
thank you for taking the time to read.

[Greg]

The Belly insulation is designed to hang UNDER the floor joists like a big blanket. The reason is simple, it allows the warm air from the heat ducts to "Flow" under the floor and keep pipes warm.
Many here have used Tyvek (house wrap) as belly material since it will allow it to breath.
A second option and possibly cost less is to heavily insulate the skirting. Mark (site owner) has insulated his in South Dakota and has claimed that the temperature under there has never dropped below freezing.

Greg

[Mark440]

I've been trying to come up with some type of "system" that would allow me to replace the belly fabric with something a little more resistant to critters. My observations concluded that pretty much nothing hangs below the bottom of the I-beams....which makes them a good target for a support structure for some sort of new belly. Main power, water, sewer, and HVAC trunk all would have to pass through the structure.

My I-beams are just over 8ft apart. Using 2x3's re-enforced on each vertical side with 3/4" flat bar steel, I can come up with a structure that will support new insulation and allow for the 4x8 sheets of metallic sided foam panels to be attached. The part that has me hung is access should there be a problem later on.....and negotiating installation of 4x8 panels in the crawl space

[yakima4$]

Install as much un faced insulation in contact with floor sheeting as possible in joist bays. Before installing insulation seal/foam all holes/penetrations of floor sheeting elec,plmg and around heat duct. Seal all joints of duct work with duct mastic. When removing existing belly board/skin leave minimum of 3 inches each side of I beams so you surface to fasten new belly skin to. Regarding duct and water lines. Try to weave new insulation around/over duct and water lines after installing insulation in joist bays. Min R-8 heat duct, R-4 water lines. More is better, insulate traps on showers and tubs. Seal holes at tub drain with piece of plastic fastened to floor sheeting. Use visqueen for belly skin this will hold up insulation in open areas with no plumbing trees hanging down and act as a vapor barrier. The reason the insulation in newer homes hangs down in the belly skin has to do with the manufacturing process at the plants. It is cheaper and quicker. Belly skin serves three purposes, transportation from plant, vapor barrier and pressure envelope.
Install visqueen on ground and use for belly skin. Patch/seal all penetrations of belly skin with spray adhesive ( 3 M bought at Home Depot or Lowes). Tack up belly skin at exterior rim joist with hand tacker, max 4 inches O.C. Close off skirting vents during winter months.
Regarding varmints getting in house. Throw under house, spring/fall the yellow block mouse killer. After two years your problem should somewhat be resolved. Plus patch any holes in belly skin with visqeen and spray adhesive. Be sure to let adhesive tack up for aprox 20 seconds before applying patch. Spray both patch material and surface patch to be applied to

[Steve-WA]

Regarding spray adhesive - I've been patching holes with 3m spray and Tyvek house wrap. Doesn't last long.

[yakima4$]

It may be the chemical make up of the Tyvek and the spray adhesive.
Works great with mil plastic or tape

[ponch37300]

Belly material needs to be able to breath. Visqueen does not allow this. That is why you should use the recommended belly mend material or some use tyvek. Both are breathable.

[yakima4$]

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I have included the HUD standards for belly skin. All of the materials listed above would stop the migration of both moisture/air. The only item visqueen would not meet is the puncture proof test i.e 40lb. You don't want the migration of moisture/odors/radon on any home. Historically MFG housing has used particle board decking (11-13/16) which equates to no perm rating/ warps easily. Now that they (the MFG housing industry) is having a hard time finding particle board some have gone to 5/8 plywood which has the glues/ resins which have the perm rating that meets site built standards. Other item to consider, most MFG housing plants do not treat/seal/caulk/foam penetrations (plmg/electrical, mechanical) of floor decking,walls nor ceiling which sets up the chimney effect. Air being drawn from under the house into the walls and up into the roof cavity. This is the reason the belly of the home is part of the pressure envelope like the walls and ceiling. The other item is that if you have no visqueen on the ground all that moisture/bad odors will move up into the house.

You can control your environment or the environment can control you.

[yakima4$]

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[ponch37300]

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I have included the HUD standards for belly skin. All of the materials listed above would stop the migration of both moisture/air. The only item visqueen would not meet is the puncture proof test i.e 40lb. You don't want the migration of moisture/odors/radon on any home. Historically MFG housing has used particle board decking (11-13/16) which equates to no perm rating/ warps easily. Now that they (the MFG housing industry) is having a hard time finding particle board some have gone to 5/8 plywood which has the glues/ resins which have the perm rating that meets site built standards. Other item to consider, most MFG housing plants do not treat/seal/caulk/foam penetrations (plmg/electrical, mechanical) of floor decking,walls nor ceiling which sets up the chimney effect. Air being drawn from under the house into the walls and up into the roof cavity. This is the reason the belly of the home is part of the pressure envelope like the walls and ceiling. The other item is that if you have no visqueen on the ground all that moisture/bad odors will move up into the house.

You can control your environment or the environment can control you.

I didn't look too hard at your attachment but from what I did read visqueen is not listed on there.

You don't want to completely stop the migration of air/moisture. A material like tyvek or actual belly material is sort of like a check valve. It helps keep air/moisture out but is still breathable so if/when moisture gets in it can let it out. Visqueen on the ground is fine. Visqueen used for belly material is not good.