Underpinning and Insulation


I have a POH that I acquired with the purchase of my park. With the cold weather upon us I have found that this unit has no insulation under the unit for almost half the unit and the tenants electric bill is almost as much as the rent. The unit is a 24X50 double wide. I’m just curious from those who have renovated units to include underside insulation have done to get the insulation up to par. I was thinking of using batts or blown in insulation with a heavy MIL plastic to hold the insulation in place before blowing it in. The underpinning on this unit is also shot and needs to be replaced. Rather than use the standard plastic that falls apart in time what are you using for underpinning to stand the test of time. I know metal is an option, but was curious of other options. Any input would be greatly appreciated.


This is a sore topic for me…

On a doublewide I have replaced the underbelly with closed cell spray foam. Looking back I would not do it again because: 1) it was too expensive at $1.50 per foot (with labor); 2) southeast Texas only gets a hard freeze once per decade and the plumbing was replaced with PEX; 3) you find all sorts of nastiness under there which is a health risk (wear a good respirator at all times if doing it yourself); 4) the windows and other areas on the home also had insulation issues, unless you plan to replace those too there is not a lot of thermal benefit.

I too spent a lot of time evaluating all the approaches to replace one. They are all very labor intensive and most of the time do not provide a good seal to the home. Batts will get animals up in them and degrade over time. Replacing with a thick plastic as suggested is nearly impossible to navigate around all the piers and plumbing. Foam board would require all sorts of intricate cutting. There really is no good way to do it unless you jack the home up a few feet.

A singlewide I have with similar energy issues I replaced the package unit with newer window units. They will run all the time, but for about 50% of the price of an old built in unit.

I would not replace an underbelly again. There may be other reasons if you’re in a much colder climate. Good luck!


Thanks for the reply. I can tell your a very hands on guy with other posts I have seen you reply to. It’s my understanding that mobile homes when built have the underside done first with the frame flipped upside down to install the mechanicals and then insulation before being flipped right side up for framing.

I have about 3 feet to crawl under the unit and measured the studs to be 16 on center with the frame getting in the way now and again. I agree with everything you say based on past experience with stick built homes. Based on the studs being 16 on center I’m hoping a combination of batts with some heavy plastic will be better than the nothing that is there now. I just wanted to see if there was something more simple or easier to try.


Do not use plastic. Plastic must only be used on the warm side of insulation otherwise you will have condensation form and saturate the insulation. The belly wrap must be able to breath. Mobile home stores have the proper material or in a pinch you can use house wrap with the exterior side down (toward the ground).