Mobile Home Weatherization – Underbelly

By weatherizing your mobile home, you have the greatest opportunity to save on heating and cooling bills by addressing the underbelly of the home. Due to the factory construction process by which they are manufactured, 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. Typically, when doing air-sealing measures in the home, you’ll get the greatest reduction in air infiltration by filling the void at the bottom. There is little to no insulation directly behind the rim joist, giving the house a broken thermal envelope. Blowing insulation at the bottom will not only give the house a true thermal cap, but will also drastically reduce air infiltration by closing the void. This is done using an insulation blowing machine attached to approximately 100′ of hose. Most big box stores offer machine rentals. Blown fiberglass insulation will be used instead of cellulose. Fiberglass is naturally water repellent, making it a much better option in comparison.

• Padded- The first thing to address before insulating the bottom is any tears 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 achieve 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 directed into 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 out 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 would not 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 fluff or elasticity.
• Perimeter blown insulation – Blowing the 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 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 stop. Treat the ends of the center in the same way, if there is no plumbing.
• Entry point – The cavities can be accessed in two ways. One option is to remove the skirting 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 through, and repairs the holes when done. Both have their pros and cons.

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