By weatherizing your mobile home, you have the greatest opportunity to save on heating and cooling 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 bottom plate insulation and the underside of the subfloor. This cavity is known as the “underbelly.” Some houses have larger ‘windows’ than others. Generally, when you do air sealing measures in the home, you will get the most reduction in air infiltration by filling the void that is the bottom. There is little to no insulation directly behind the rim joist, giving the house a broken thermal envelope. Blowing insulation to the bottom will not only give the house a true thermal limit, it will dramatically reduce air infiltration by closing the void. This is done using an insulation blowing machine coupled with approximately 100′ of hose. Most big box stores offer machine rentals. Blown fiberglass insulation will be used instead of cellulose. Fiberglass is naturally water repellant, making it a much better option in comparison.

• Padded- The first thing to address before insulating the bottom is any rips or holes the bottom board may have. If they are not fixed, then there is nothing to hold the insulation. The most cost effective way to accomplish this is to use “Tyvek or Typar” house wrap as the closure material. You can staple this to the existing material or you can use screws and washers aimed at the bottom of the floor joists. For smaller holes or to seal patches, two-part spray foam insulation works well.
• Blown insulation in the center of the mobile home – The key to blowing insulation is knowing where to place the material. Mobile homes were designed so that the plumbing lines would run through the floor near the heating duct so they wouldn’t freeze in the winter months. The center of the house, where there are pipes, must be blown with low density. Do not over-insulate, otherwise the heat from the heat pipe cannot reach the pipes and they will definitely freeze. You want to install the insulation where you are filling the cavity, but the material still has some fuzz or stretch.
• Blown insulation around the perimeter – 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, watch out for plumbing, there are usually a couple of these sections that have plumbing. Blow the insulation to maximum density, filling the void completely and packing the material. This is where air infiltration and radiant heat loss/gain from the bare rim joist stops. Treat the center ends in the same way, if there is no plumbing.
• Entry point – Cavities can be accessed in two ways. One option is to remove the baseboard or siding from the exterior and drill holes through the rim joist. An aluminum pole attached to the insulation blow hose is normally used to enter the cavity. The other crawls under the house and cuts holes in the bottom board, inserts the hose straight in, and repairs the holes when finished. They both have their pros and cons.

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