below right. Using an Undersill Molding (A): Build out an undersill/utility molding with a furring strip to the proper dimension. Snap lock the properly fit Insulated Siding panel, and slide into undersill molding checking for proper free movement. A Dual Undersill Molding, or Snap-in Crown Molding may also be used to secure the top course of siding. When using a Snap-in Crown Molding, the top of the panel will be nail slot punched, instead of snap-lock punched. Vertical Siding Installation Preparation When installing vertical siding, however, follow these additional preparatory steps: Install horizontal furring strips, 12" on center, or a solid nailable sheathing prior to the siding, if needed, to level the surface or provide sufficient material for 3/4" fastener penetration. Snap a level chalkline around the base of the sidewalls. Typically, the chalkline is positioned so that the bottom of the J-channel that will serve as a vertical starter strip is 1/4" below the lowest point on the wall that will be sided. Install J-channel along the chalkline as a receiver for the vertical siding. As with horizontal siding, when installing vertical siding it is necessary to install several accessories first, including corner posts and window, door, and roof trim. Outside and Inside Corner Posts Leave 1/4" gap at the top of corner posts. Place the first nails in the uppermost end of the top nail slots to hold them in position. Place all other nails in the center of the slots. Nails should be 8" to 12" apart.