By weatherizing your mobile home, you have the greatest opportunity to save on heating and air conditioning bills by addressing the most vulnerable part of the home. Due to the factory construction process by which they are constructed, they have a large open cavity between the underlayment insulation and the underside of the subfloor. This cavity is known as the “belly.” Some houses have larger ‘basses’ than others. Typically, when you perform air seal measurements at home, you will get the greatest reduction in air infiltration by filling the void that is the belly. There is little to no insulation directly behind the edge beam, giving the house a broken thermal envelope. Blowing insulation into the belly will not only give the house a true thermal limit, it will dramatically reduce air infiltration by closing the vacuum. This is done using an insulation blowing machine in conjunction with approximately 100 ‘of hose. Most large stores offer machine rentals. Blown fiberglass insulation should be used instead of cellulose. Fiberglass is naturally water repellent, making it a much better option in comparison.

  • Patchwork – The first thing to address before insulating the bottom is any tears or holes the bottom board may have. If they are not fixed, there is nothing to hold the insulation. The most cost effective way to achieve this is by using a house wrap “Tyvek or Typar” as the closure material. You can staple this to existing material or you can use screws and washers aimed at the bottom of the floor joists. For smaller holes or to seal patches, the two-part spray foam insulation works well.
  • Insulation blown into the center of the mobile home – The key to blowing insulation is knowing where to put the material. Mobile homes were designed so that the plumbing lines run through the floor near the heating duct so as not to freeze in the winter months. The center of the house, where the plumbing lines exist, should be blown with low density. Do not insulate too much, otherwise the heat from the heat conduit cannot reach the pipes and they will freeze permanently. You want to install the insulation where you are filling the cavity, but the material still has some fluff or foam in it.
  • Perimeter blown insulation – Blowing insulation around the house, including the ends only if they don’t have plumbing nearby, is where you get the most bang for your buck. The perimeter is defined as the outside of the I-Beam sections. Again, be careful with the plumbing, there are usually a couple of these sections that have plumbing. Blow out the insulation at maximum density, filling the void completely and packing the material. This is where air infiltration and radiant heat loss / gain from the bare edge joist stops. Treat the center ends in the same way, if there are no pipes.
  • Entry point – The cavities can be accessed in two ways. Removing the baseboard or siding on the outside and drilling holes through the edge joist is an option. An aluminum post attached to the insulation blowing hose is typically used to enter the cavity. The other crawls under the house and pokes holes in the bottom board, inserting the hose directly and patching the holes when complete. Both have their pros and cons.

By keeping these ideas in mind, you can easily and safely weatherize the most vulnerable part of your mobile home.

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