How to Build an Addition on a Single Wide Trailer

Framing

• 1

  Measure the dimensions for the addition. Hammer 2 by 2-inch stakes into the ground at the four corners of the addition. Place the freestanding structure as close as possible to the trailer. Dig the holes for the foundation footing at 4-foot intervals. Make the width of the holes 12 inches and the depth 12 to 18 inches. Refer to local codes for exact footing specifications and for preparing the bedding.

• 2

  Insert a cylindrical form in each hole. Fill the forms with quickset concrete mix. Insert the bolts for the post bracket in each footing before the concrete cures. Make sure at least 1 inch protrudes above the surface of the footings. Secure post brackets to the footings with washers and nuts. Insert 4 by 4-inch posts into the bracket and fasten with 1/4-inch diameter lag screws.

• 3

  Make the final level of the addition’s floor close to the height of the floor leading from the existing structure. Frame the floor system with 2 by 8-inch lumber. Place the floor joists 16 inches on center. Install floor installation per the manufacturer instructions. Screw the 3/4-inch plywood to the floor joists with 1 1/2-inch screws to create the subfloor.

• 4

  Construct the wall sections with 2 by 4-inch stud-grade lumber. Cut two boards of equal length to form the top and bottom plate for each wall section. Cut the studs and place them 16 inches on center.

• 5

  Mark the width of the rough opening for the door on the bottom and top plates. Place the studs on each side of the door opening -- called king studs -- 1 3/4-inches from the rough opening mark.

• 6

  Frame the door opening in the wall section. Measure and cut two 2 by 4-inch boards, which forms the top of the frame called the "header." Make the height of the rough opening 2 to 3 inches higher than the door.

• 7

  Raise the wall in place and fasten the wall to the floor with 2 1/2-inch-long nails. Repeat this process for each wall section.

• 8

  Build the roof by placing 2 by 8-inch rafters at 16- or 24-inches on center. Make sure the rafters have the proper slope – usually 1/4 per foot -- away from the trailer. Cover the roof with 1/2-inch plywood. Use roofing nails to mount the plywood to the roof rafters.

• 9

  Cover the plywood with felt paper and nail in place. Follow the manufacturer's instructions for installing roof shingles or other roof covering.

• 10

  Seal the gap where the addition meets the home. Screw a 1 by 6-inch board to the trailer on each side of the addition. Cut a 3 1/4-inch-wide piece from a 1 by 4-inch board. Set the saw at 10 to 15 degrees for a bevel cut. Pre-drill at least six holes through the edge of the 3 1/4-inch board.

• 11

  Apply weatherstripping to the side of the 3 1/4-inch-wide board opposite the beveled edge. Place this board flat against the addition and butt the bevel edge of the board against the 1 by 6 secured to the trailer. Insert 4-inch-long screws through the pre-drilled holes. Caulk along the joints to seal.

Interior

• 12

  Shut off the electricity at the trailer's main electrical panel. Run electrical wires in the wall sections for the switches and outlets. Connect electrical wires and components in accordance with local electrical codes.

• 13

  Staple fiberglass batt installation between ceiling joists and wall studs. Follow the local build codes for recommended R-value. The R-value refers to the insulation's capacity to prevent heat flow.

• 14

  Mark the wall opening on the trailer wall opposite the door opening. Remove the wall material and framing. Follow the manufacturer's instructions for installing the door in the addition's wall section.

• 15

  Screw 5/8-inch drywall to the ceiling and wall sections. Apply drywall tape to the seams and finish with joint compound. Sand the surface to a smooth finish and paint.