Insulation R-value for underbelly?

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cskal
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Joined: Sat Jun 27, 2009 6:38 pm
Location: NEPA

Tue Sep 01, 2009 8:53 pm

I am getting my information together for materials and approximate cost to replace the entire underbelly of my 24x48 double wide. The critters have essentially torn down any insulation that was there. I plan on buying a pair of the 16x80 belly paper rolls from the site; the insulation would come from the local hardware or Lowes/HD. I will fix the critter access first and re-plumb with PEX before underbelly replacement.

The cert for the home lists the floor insulation as R-7 @ 2.5" thick and I can believe it after seeing underneath the home, but what is listed for the rest of the home I can't believe, it reads like a pipe dream (walls and ceiling R-18 @ 18" insulation thickness).

What R-value insulation should I use for the underbelly? I guess R-19 would be an upgrade from the laughable R-7 they claim for the floor. I am assuming R30 would be overkill (in price as well). I am in NE PA so we get a fair amount of cold weather, on average the winter lows are around 5-10* standing air temp with forays into the -10* area. The cert has me listed for outdoor winter design temperature zone 2.

All input appreciated.


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JD
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Wed Sep 02, 2009 9:01 am

I use R-19 on my belly repairs if I am replacing all of the insulation. Generally, I try to match what is already used on the home if it is just a repair. Having a consistent thickness of insulation keeps the flow of cold/warm air even throughout the home without channeling it to other areas.

If the home was built with more than R19, then by all means, use that R value insulation. I am in a warm area and have never seen that though.

JMO
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All information and advice given is for entertainment and informational purposes only. The person doing the work is solely responsible to insure that their work complies with their local building code and OSHA safety regulations.

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Greg
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Wed Sep 02, 2009 5:04 pm

I would take it to at least R19. The Underbelly & skirting also in good shape and as air tight as possible. Many have also used rigid foam behind the skirting to add more insulation. Greg
"If I can't fix it, I can screw it up so bad no one else can either."

sohappy
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Joined: Thu Sep 03, 2009 10:27 pm

Thu Sep 03, 2009 10:37 pm

R-33 should be the minimum you install. If you check local bldg codes for Energy efficient homes they will point you in the right direction. Also insulation should be installed up tight to the floor, make sure your ducts are wrapped and your water lines mid depth in the insulation. Belly skin needs to be tight and all tears sealed for air leakage, spray adhesive in a can works great. While the belly is open seal your ducts,joints,seams with mastic and replace cross over with metal.It comes in tubs and can be wiped on with gloves. Check your local heating and cooling contractor for mastic

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Greg
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Fri Sep 04, 2009 5:20 pm

sohappy, If you pack the space under the floor totally full and you live in a cold climate I have a feeling you won't still be so happy when the pipes freeze. You NEED air space under the floor to allow warm air to reach the pipes. Greg
"If I can't fix it, I can screw it up so bad no one else can either."


sohappy
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Sat Sep 05, 2009 12:26 am

I should have described this better. Easy way,install R-19 first between foist and up tight to floor. Next install pex up tight to joist.Next install another layer of R-19 .This would be the same as site built and if there is a leak/tear in belly skin cold air does not affect whole floor cavity. Insulation hangs down below pipes because of the manufacturing process at the plant its easy,fast and cheaper that fitting around the floor joist. Also should seal/foam any holes in floor decking,water lines,plumbing pipes, elect wires and especial the tub p-trap access holes (use a sheet of plastic and staple up to floor decking. Of course close skirting vent during the winter

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Yanita
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Mon Sep 07, 2009 10:08 pm

Hi,

That is am improper install for a mobile home...

First your ducts run close to the underside of the floor, then your water lines are typically close to that. Your insulation is then installed and NOT tightly as you need air space. This allows the radiant heat from the ducts to circulate around the water lines to help prevent freezing in the winter.

After insulation is installed then your MH rated underbelly material is hung in place, this also helps support the insulation and keeps heat in, cold out...

Sealing up the holes is proper , but using plastic has been done but it is not the proper repair.

Yanita
The difference between success and failure is who gives up first!

cskal
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Joined: Sat Jun 27, 2009 6:38 pm
Location: NEPA

Tue Sep 08, 2009 11:22 am

Yanita's post is more in line with my thinking. While more insulation can't hurt as sohappy suggests, I am in a cold climate during winter. Since 99% of my heating is done with a pellet stove and not the furnace, I have to have ambient heat able to move through the floor to the pipes. Insulation between the joists would block this heat flow. For the past two years I have had the pellet stove as the primary source of heat with no freezing pipes despite near zero and subzero standing air temps combined with the underbelly being almost completely torn down everywhere. I am working to fix this hopefully before the (serious) cold weather arrives in and around the November/December time frame.

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