Let’s Talk About Bottom Board

I know that all too often we take for granted the importance of that black, plastic-like material that stretches under the floor of manufactured homes. Some folks, (and the manufacturer’s installation instructions), call it bottom board. Others call it “underbelly” or “belly board” or some other name, but for today, lets just call it “bottom board”.

Obviously the bottom board is needed to secure and protect the floor insulation, and keep critters out of the floor cavity. But that is only half of the story.

I am certain that you have had your customers ask you why the holes cut in the floor decking for drain lines are often over cut. Why does the factory cut 2 ½” holes for a 2” pipe? What about the big hole for the bathtub “P” trap? We all have seen homeowners stuff insulation around these pipes in an effort to reduce heat loss. But is this necessary?  Not really!

Leaking “P” trap was fixed, but the installer failed to replace the insulation and repair the bottom board!

If you look under the floor decking, you will see cables, drain lines, water supply lines and most likely, un-insulated metal heat ducts. These un-insulated heat ducts keep the entire floor system warm in the winter, and prevent the water pipes from freezing. Since the floor cavity is in a sense “conditioned space” those holes in the floor decking are not a path of heat loss or air infiltration. So, what keeps the outside, unconditioned air from getting inside of the floor cavity? The Bottom Board!!

Water lines in the floor. Be sure to replace the insulation and access panels to keep from freezing!

The bottom board acts as the pressure envelope, which is the primary air barrier to limit air leakage. With that in mind, we should start thinking about the bottom board as less of a part of the transportation system, and more of a thermal component which is critical to the overall performance of the manufactured home’s energy efficiency!

The red line represents the pressure envelope that is intended to contain the conditioned air inside the home.

Consider the impact of every hole, slice, cut, tear or missing access panel of the bottom board.  They all allow unconditioned air to enter the floor cavity. This unconditioned air can cause significant damage to the home. In summer months, it can cause condensation to form on the heat ducts, and promote the growth of mold and mildew. In the winter, it can cause higher heating bills, and could impact consumer comfort.

The manufacturer’s installation instructions all require the installer to “Repair and Seal Bottom Board”.  For new homes, make sure you inspect the bottom board upon delivery, and report any holes, tears or road damage to the manufacturer. If you need to make any repairs, follow the information in the manufacturer’s installation instructions. Replace missing, wet, damaged or dirty insulation. Allowing wet insulation to dry out does not make it as good as new, it must be replaced. Just be sure to maintain the same R value as was originally installed in the floor.

Tape over lag bolts with an approved bottom board tape.

Make certain that the material you use to make any repairs or patches are appropriate for the job. I know a lot of installers use “Flex-Mend” with great success, and it is approved for this application.  If the area to repair is too large, use staples and a backer board of ¼” plywood or similar materials.  On multi-section homes, you should tape over the lags used to secure the floors together.

Be sure to clean the surfaces where the patch is to be applied. The HUD Code clearly states that any patches must be just as durable as the original bottom board material, see 24 CFR 3280.305(g)(6). Duct tape is not approved for bottom board repairs!

Duct Tape is not an approved material for repairing bottom board.


If you are a professional installer that is using the Complete Installation Checklist for every home you install, you already know that there is a line item for bottom board holes and tears.

I hope that installers, retailers,  community owners, and consumers are on the lookout for cable television, telephone, or satellite dish service technicians that have no respect for the importance of the bottom board under our homes. Their all too common practice of slicing open the bottom board to fish their cables and wires, must stop!

Bottom Board cut in two places for fishing cables.

Finally, many savvy industry professionals are now performing annual service inspections on their customer’s homes. For those of you that provide this service, make sure bottom board repair/patching is on your inspection checklist. If you don’t offer annual service inspections, maybe you should. It can be a money maker for you, and a money saver for your customers.

Introducing Manufactured Homes To Their New Owners

Throughout my career, my involvement with manufactured homeowners has been after they lived in their homes for a while. As a result, I have heard more than my share of complaints, questions, misunderstandings, and fake news! This led me to conclude that we could certainly do a better job introducing these new manufactured homeowners to their homes.  So, as a  start, here is my list of the top 10 things we should talk about with our customers:

1.       The importance (and location) of the data plate.

I know they are required to be permanently attached to the home, but we all know that far too many data plates peel off the walls, get painted over, or otherwise disappear from the home. Explain to your customer that the data plate should be preserved. Especially should they ever want to sell the home. If it peels from the wall, it should be saved with other important documents. 

2.       The Importance of the Certification (HUD) Label.

Like the data plate, tell your customer about the importance of preserving the certification label(s). Not only in the event of a future sale, but it will be needed to re-finance or for relocation. 

3.       That tripping one Ground Fault Circuit Interrupter (GFCI) receptacle can shut off the power to other receptacles in the home. 

A GFCI receptacle can often serve multiple outlets.

Show your customers how GFCI protection is provided in each bathroom, outside receptacle, heat tape receptacle, receptacles serving kitchen counters, and certain locations within 6′ of wet bar sinks. Make sure they know that while some receptacles that don’t have a test button, they are still protected!  Show them how to test the GFCI, and reset them as well! (Search the HUD Code at 24 CFR 3280.806(b) for exact locations)

4.       The importance of the Bottom Board under the floor of the home. 

Notice the slice left by the telephone man!

We all know that installers of cable or satellite television, telephones, etc. always slice holes in the bottom board of the home to run their cables. Not only do we need to warn our homeowners about attacks from these “technicians”, but inform them how the bottom board is critical for keeping conditioned air in the floor cavity where it belongs! Remember, the bottom board is not only intended to prevent critters from getting into the floor, it also serves as the pressure envelope enclosure. Holes in the bottom board mean losing conditioned air into the crawl space, and lead to higher energy costs!

5.       Make sure any future landscaping doesn’t impede water from draining away from the home.

This landscape design led to foundation problems!

Landscape timbers, flower beds, or mulch borders can easily trap water and direct it right into the crawl space! Talk to the homeowner about the importance of allowing water to drain away from the home. Once you have completed your site grading, take pictures for your home file as evidence that you did your job properly!

6.       That smoke alarms are generally equipped with a hush bottom.

This smoke alarm has a separate HUSH button.

Far too many people have told me that they disconnect their smoke alarms because of nuisance alarms caused by smoke from cooking.  We certainly know that this is a dangerous practice, but have we introduced our customers to the alternative solution? Tell folks that pushing and holding the test button (or a separate hush button) will temporarily silence the alarm. This is a much better idea then disabling the alarm!

7.       That a carbon monoxide alarm can be added to their home at a minimal cost.

Typical CO Alarm, simply plugs into a wall outlet.

Just because the Manufactured Housing Construction and Safety Standards (HUD Code) doesn’t require a CO alarm, doesn’t mean you can’t add one. More and more local municipalities are requiring every home with fuel burning appliances, and/or an attached garage, to be equipped with a carbon monoxide alarm.  I think we would be wise to get ahead of this, and provide the same level of protection as required in other residential building codes. I suggest ordering homes with an extra receptacle in the hallway (outside the bedroom areas) just for this purpose. You might just save a life!

8.       That the water temperature at the showers and bath tubs is limited by anti-scald fixtures for their safety.

This is one type of anti-scald fixture.

The general complaint is that the water is not hot enough. Take a few minutes to explain how the anti-scald fixture limits the water temperature to 120°. Remember, Installers are required to check the water temperature at each tub and shower.  Click Here to read an earlier post on this topic.

9.       How they can bring fresh air into the home  (whole house ventilation) without opening the windows or doors.

Switching the FAN to ON often activates the whole house ventilation system.

I have always been a big fan of the whole house ventilation systems designed to introduce fresh air into every manufactured home. When people complain of poor indoor air quality, I would ask if they were familiar with the ventilation system. Most of the time, the answer is no!  Sometimes it is operated by a switch in the thermostat (or automatically whenever the furnace blower runs), sometimes it is a simple exhaust fan in another area (like utility room). Either way, make sure our customers know about this feature. 

10.   That the home is not designed for future additions or modifications.

Keep these structures independent of the home

Remember, typically a manufactured home is not designed to support the added weight of carports, garages, three season rooms, etc. Not to mention how these after-market additions can add to the wind load imposed on the home.

 Hopefully, you are already talking about these items with your customers. If not, consider how the extra few minutes spent educating your customers can bolster their overall satisfaction with their home. I think you will find it will be time well spent!