Insulation is one of the most important materials in your home. Without proper insulation, your home can be draughty and require more money to heat and cool. Whether a mobile home or custom-built house, when it comes to insulating your crawlspace the procedures are the same. The only difference is whether your crawlspace is ventilated (meaning there are either vents or perhaps other openings in the mobile home's skirting) or unventilated (sitting on an airtight foundation.)
Access the mobile home crawlspace. Spray expanding spray-foam insulation into any holes present in the floor above. Fill holes completely and allow them to dry.
Measure and cut, using a utility knife, sections of fibreglass insulation to fit between the floor joists under the floor. Note that since these run width-wise, the insulation lengths will measure about the width of the trailer. Use unbroken sheets between joists when possible.
Push each length of insulation tight against the floor above, paper backing (vapour barrier) side up, against the floor. Hold in place and push a wire insulation support underneath the insulation and between the floor joists. Press the wire up until it firmly pushes and holds the insulation up without compressing the insulation. Continue supporting the insulation along the entire section length, placing wire supports every 18 inches.
Spread a sheet of belly board (polythene -- a tarp-like material) across the underneath of the floor and insulation. Start at the outermost edge, nailing it to a lathe strip, and pull snugly across the underneath of the supported insulation. Secure the edges around the perimeter, nailing every 12 inches.
Attach sheets of styrofoam insulation underneath the belly board, to further insulate, support, and prevent animal damage to the belly board. Starting in a corner, hold the sheet up and nail to the lathe strip along the edges and the floor joists across the body of the trailer. Find the joists you nail into by pressing lightly to feel where it is firm. Nail every 12 inches down the joist length.
Inspect the crawlspace, noting leaks in the skirting or foundation along with the floor above. Seal any leaks present using expanding spray-foam insulation.
Cover the entire area of ground with plastic sheeting, extending the ends of the plastic up the crawlspace walls about a foot. Secure the plastic to the wall with a bead of construction adhesive. Overlap any joints, if you are unable to use an unbroken sheet of plastic, by about a foot. Hold the plastic and any seams down, placing rocks, scrap wood or similar objects on top.
Nail or glue, using construction adhesive, furring strips running horizontally along the entire length of the crawl space wall, about a foot above the ground. Measure and cut fibreglass insulation, using a utility knife, into sheets measuring a couple feet longer than the crawl space wall is high. Nail insulation to the joist at the top of the wall and to the furring strip below. Tape seams, if desired, using vinyl tape.
Substitute rigid insulation for fibreglass as desired. Use a power-actuated gun to drive nails into concrete, instead of gluing furring strips, if desired.
Check local building code to determine building requirements in your area. Wear protective eye wear, a face mask, gloves and long sleeves when working with fibreglass insulation, to protect yourself. Fibreglass insulation is composed of glass, which can scratch you and cause problems if you get it in your eyes or inhale it.