How to Repair a Mobile Home Belly Board

Repair A Mobile Home Belly Board

If you’ve ever read the government published pamphlets about a mobile home underbelly or how to repair a mobile home belly board you’ll quickly notice that they aren’t particularly worried about cost. Every recommendation usually ends with ‘hire a professional.’ But us regular mobile home owners have budgets and can’t just call up a pro every time we need something fix. For us, it’s either DIY or not at all.

In this article, we cover how important the underbelly of your home is and how to repair a mobile home belly board yourself in one weekend, maybe even one day if you’re organized and have lots of help.

Belly Board Vs Underbelly Vs Vapor Barrier

The terms belly board and underbelly are a bit confusing. Both have ‘belly’ in their name and both reference something under a mobile home. So what’s the difference between the two terms?

The belly board is also called belly wrap, rodent barrier, bottom wrap, bottom board, belly, belly barrier, and Cemplex. The belly board looks like plastic but it’s actually stronger. In fact, it has fabric weaved into it so that animals can’t easily tear it. The black material also allows just enough circulation to keep condensation, mold, and mildew to become an issue.

Belly board is made of polyethylene sheeting that is woven to make it harder to tear or penetrate.

The underbelly is the area that the belly wrap covers from the bottom of your sub-floor to the top of the belly board. This includes the chassis, insulation, HVAC venting, and plumbing.

There is also a vapor barrier which is an entirely separate thing from a belly board. The vapor barrier lays on the ground and helps keep moisture from the ground to rise and create issues under your mobile home. A vapor barrier is also much more important than many mobile home owners realize and should be installed if the home doesn’t have one. HUD recommends that the vapor barrier extend at least 6 inches from the perimeter of the home. This also helps keep weeds down which keeps weedeater damage from happening.

How Does a Belly Board Get Damaged?

Damage to a mobile home underbelly is most commonly caused by animals. However, repairmen are also notorious for leaving the black fabric open after they finish repairs.

PS When hiring professionals to make repairs under your home make sure the total cost includes repairing the belly board.

Damaged Vs Healthy Underbelly and Belly Board

Does your mobile home look like the next image underneath it? If it does, you need to learn how to install insulation under your home, repair the HVAC ducts, and then how to install a new belly board. Hopefully, this article should help you with the last part.

How to Repair a Mobile Home Belly Board 1
Damaged mobile home underbelly. (Source: Dept of Energy)

Four things are happening (or have happened) when a mobile home belly looks like this:

  • a lot of heating and cooling loss is likely occurring wherever the insulation is missing or damaged
  • critters can get direct access to the home
  • plumbing lines are more susceptible to freezing
  • the floor joists and subflooring has no protection from moisture

If a mobile home underbelly looks like the image above you should never buy it. In fact, the underbelly of a mobile home is so vital to the whole health of a home that you should always look under the home before you even go inside. The condition of the home’s underbelly and belly board will tell you everything you need to know about the home. If it looks like the image above the home has not been adequately maintained or kept up. It’s probably best that you move on to the next home unless you get a really good deal on it.

This next image is how a mobile home underbelly and belly board should look. Since the home is sitting on a concrete slab it doesn’t need a vapor barrier.

Underbelly And Blocks Under A New Manufactured Home With Tie Downs
Image Source Unknown

How to Repair a Mobile Home Belly Board

Repairing or replacing a mobile home underbelly and belly board is a tough job, not gonna lie to you about it. It’s tedious and frustrating but it can be done with some careful planning and help from friends and family.

Before you begin you will want to lay down the ground moisture/vapor barrier. This helps protect you from getting nasty while under the home.

First, everything has to be removed. The old insulation and the black belly board will need to be carefully cut out and taken away so that you are left with just the floor joists, HVAC ducts, plumbing pipes, and the subfloor.

Step 1: Remove the torn insulation and black belly board

First, you will need to remove and discard the old insulation and belly board. Once everything is removed you can start repairing and replacing each element one by one.

Step 2: Reseal or Replace the Ductwork

Next, you will replace or reseal the duct work. Make sure all the corners and seams have been taped together or replaced.

repairing a mobile home underbelly and damaged HVAC Vents
This is a damaged duct under a brand new manufactured home after installation. Transport can damage duct work easily. (Source: PA WTC/

Step 3: Inspect Plumbing

Next, you’ll want to make sure your plumbing is healthy. This is a great time to run new water lines. You can always cap off the old lines and run the new pipe (PEX) right beside the ductwork. If you live in a cold climate it’s a good idea to run your water supply lines beside the duct work so the heat can help them from freezing.

Step 4: Install Insulation

Next, you’ll want to install new insulation. There are a few different methods and materials available. Most people like to use batts or rolls of insulation but foam board insulation is a good choice too. Read our insulation guide here and our underbelly foam board insulation tutorial here.

Step 5: Install the New Belly Board

Once the insulation is installed you will replace the belly board or the black plastic/fabric material that encloses the entire home.

If your belly board is present but has holes you can patch it with a few different products. There are zipper patches for areas that you need to access more than once. Tape is also a good patch material, just cut to length and keep adding it till the hole or rip is covered.

Here’s a great video showing how to repair holes in your plastic belly board:

Misc Tips

You can buy a product called the Trap Flap for areas in your belly board that require easy access. It’s just a piece of belly board with a zipper on it but it could be useful.

I once read a tip about repairing and replacing mobile home belly board that kinda made sense and kinda didn’t. I’m sharing it with you because it could help.

One of the reasons that many homeowners don’t like to have a belly board installed under the home is the difficulty when it comes to repairing plumbing or ducting (or even wiring).

Belly board also makes finding a water leak difficult. One installer recommends taking a small safety pin and pushing through the belly board a few times under bathrooms and kitchens. This makes moisture or wetness easier to see, especially if you have a nice dry vapor barrier on the ground. You may be able to catch leaks a little quicker.

This could be a terrible idea for bug-prone or extremely wet areas though. Just thought I’d share the tip.

Vapor Barrier And Belly Wrap Under Mobile Home

Can you Use Tyvek as a Mobile Home Belly Board?

If you’ve read other mobile home blogs or the University of Wyoming’s booklet titled Mobile Home Energy or even the US Department of Energy you’ll see a recommendation using Tyvek to repair belly board.

Here’s their steps to repair a mobile home belly board with Tyvek:

To repair large holes in the belly board (generally in the central part of the belly between the two main steel beams) use the following procedure:

First, measure the space needed to be covered. Cut a piece of Tyvek that is at least 1 foot larger than the hole on all sides. If the hole is really large, wrap one edge of the Tyvek around a long 1×2 inch furring strip.

Screw the 1×2 to the bottom of the floor joists next to one of the steel I-beams. Drape the fabric under the main duct trunk line so that space for insulation remains. Wrap the opposite edge of the replacement fabric to another 1×2 furring strip, then screw it to the joists next to the other metal frame.

Glue and stitch the other two sides of the replacement fabric to the existing belly.

Mobile Homes 0052
Image PA WTC US Dept of Energy

In my opinion, the cost of real polyethylene belly board isn’t enough to warrant using Tyvek as a replacement. Plus, Tyvek is a material that allows condensation or moisture to escape the home by design and you don’t want that happening under your home. You certainly don’t want moisture from the ground entering the underbelly. The whole reason we install vapor barriers and belly board is to keep moisture from penetrating the home. Tyvek also doesn’t have the oil additive that keeps mice from chewing on it like real belly board.

With that said, I think any kind of belly board, whether it be foam, Tyvek, or just blue tarps stapled up is better than nothing.

As with all mobile home construction and repair topics, everyone will have a different opinion. Everyone thinks they are right and everyone else will be wrong. Try to read the most popular blogs on the topic you’re researching and pull the most useful information from each. Of course, if you have any questions just leave them in the comments below and I’ll try to help.

In Conclusion

As always, thank you so much for reading Mobile Home Living®!

2 thoughts on “How to Repair a Mobile Home Belly Board”

  1. Thank you so much for this article. We desperately need repairs on our ductwork, insulation and belly board. We have basically gutted and rebuilt most of the inside of an older mobile home and are over budget. Since day one I have been saying that we absolutely need these repairs but no one who has worked on our place seems to understand. Even a contractor who regularly works on mobile homes in our area seems baffled as to what needs to be done. I love what we have done inside and want to protect it. Thank you. Any suggestions on finding someone who can do this work?

    1. Hi Kim!
      Glad it was helpful for you. I wasn’t really aware of the importance until I kept reading all the manuals and books. Every one of them stressed the importance and it makes sense, you don’t want moisture or critters to reach the insulation and all the other stuff under there.
      Unfortunately, it’s really hard to find anyone that is willing to work on mobile homes and especially if it’s a job that requires going under a mobile home. A handyman or a manufactured home installation company are probably your best bet.

      Best of luck! Let me know how it goes!

Leave a Comment

Your email address will not be published. Required fields are marked *