Before the siding itself can be hung, a number of accessories must be installed first, including starter strips, corner posts, window flashing, trim, and J-channels over the roof lines and around openings.
Outside and Inside Corner Posts
A water-resistive material should be used to flash the inside and outside corners a minimum of 10” (254mm) on each side before installation of the corner posts (Fig. 26).
NOTE: Depending on the type of construction, vinyl soffit and fascia or the corner posts can be installed first.
Inside corner posts can be a single or double J-channel, or a factory-formed inside corner.
Place the corner post in position, allowing a 1/4” (6.4mm) gap between the top of the post and the eave or soffit. Position a nail at the top of the upper slot on both sides of the corner post, leaving a gap of approximately 1/32” (0.8mm) between the nail heads and the corner posts. The corner post hangs from these nails. The balance of the nailing should be in the center of the slot, 8” to 12” (203mm to 305mm) apart, again leaving 1/32” (0.8mm) between the nail head and the corner post. This allows for the expansion and contraction to occur at the bottom. The corner post should extend 3/4” (19mm) below the starter strip. Make sure the posts are plumb (i.e., vertically straight) and square to the wall (Fig. 27 and 28). Cut away any exposed nail hems.
If more than one length of corner post is required, overlap the upper piece over the lower piece by cutting away 1” (25.4mm) of the nailing flange on the top piece. Overlap 3/4” (19mm), allowing 1/4” (6.4mm) for expansion. This method will produce a visible joint between the two posts, but will allow water to flow over the joint, reducing the chance of water in infiltration.
Capping a Corner Post
Corner posts on homes with a second-story overhang need to be capped by making the cuts shown (Fig. 29). Fold the flaps created over each other as indicated.
Drill a 1/8” (3.2mm) hole in the center, through both layers of vinyl, and install a pop rivet to hold them in place. Cut a notch in both layers to allow clearance for the corner.
In order for the siding to be installed properly in a level fashion, the starter strip at the bottom of the wall must be level.
Determine the lowest point of the wall that will be sided; from that point, measure up 1/4” (6.4mm) less than the width of the starter strip and partially drive a nail at one corner.
Attach a chalkline; go to the next corner and pull the line taut.
Make sure the line is level by using a line level or a 4’ (1.2m) level.
Snap the chalkline and repeat the procedure around the entire house.
Optional method to determining the position of the starter strip in new construction and some re-siding applications: Measure down from the soffit at one corner of the house to the top of the foundation and subtract 1/4” (6.4mm) less than the width of the starter strip. Make a mark on the wall and record the measurement. Transfer the measurement to the other corner of the wall. Snap a chalk line in between the corners at the marks. Repeat the procedure around the entire house.
NOTE: When insulation or backerboard is used, fur the starter strip, if necessary, to accommodate the thickness of the sid- ing. For a vertical siding starter methods, see the section on vertical siding.
Using the chalkline as a guide, install the top edge of the starter strip along the chalkline, nailing at 10” (254mm) intervals. Allow space for the corner posts, J-channels, etc.
Keep the ends of starter strips at least 1/4” (6.4mm) apart to allow for expansion (Fig. 30).
Nail in the center of the starter strip nailing slots.
For insulated siding, the starter strip needs to be spaced away from the wall to accommodate the thickness of the backing on the siding. Consult the manufacturer’s instructions for specific materials or techniques.
NOTE: In certain situations, it may be necessary to use J-channel as a starter strip; remember to drill minimum 3/16” (4.8mm) diameter weep holes no more than 24” (610mm) apart.
Windows, Doors, and Roof Lines
Flashing New Window Installations
If installing both a new window and flashing, refer to window manufacturer’s instructions and ASTM E2112, Standard Practice for Installation of Exterior Windows, Doors and Skylights for the proper flashing installation method for the window type and wall configuration on the project.
Flashing Previously Installed Nail Fin Windows
If a nail fin (in new construction) window has been previously installed without flashing, the following instructions should be followed:
Apply a continuous bead of sealant to the nailing flange of the sill in a manner that covers the nails and nail slots. Apply a minimum of 9” (229mm) wide horizontal sill flashing level with the bottom edge of the existing window by pressing the flashing into the sealant bead at its top edge. Cut the sill flashing long enough to extend a minimum of 9” (229mm) beyond each jamb. Fasten the sill flashing at the bottom and side edges (Fig. 31).
Apply a continuous bead of sealant to the nailing flange of the jambs in a manner that covers the nails and nail slots. Continue the bead of sealant at the jambs vertically a minimum of 8 1/2” (216mm) above the head of the window to allow for bedding the top portion of the jamb flashing into sealant in the next step. Install the jamb flashing by pressing the flashing into the sealant beads at the window jambs. Extend the bottom edge of the jamb flashing approximately 1/2” (12.7mm) short of the sill flashing edge, and extend the top edge approximately 8 1/2” (216mm) beyond the head of the window, where the head flashing will be placed next. Fasten the jamb flashing along the edges further most from the window (Fig. 32).
NOTE: Sealant should be compatible with window, flashing, and water-resistive barrier materials. Contact sealant manufacturer for job-specific recommendations.
Apply a continuous bead of sealant to the nailing flange of the head in a manner that covers the nails and nail slots. Add an additional bead of sealant horizontally, in line with the top of the head flashing. Install the head flashing by pressing the bottom edge of the flashing into the sealant bead previously applied across the mounting flange. Extend the ends of the head flashing approximately 1” (25.4mm) beyond the jamb flashing at each end. Fasten the head flashing into place along the top edge (Fig. 33).
Flashing Previously Installed Window with Exterior Casing (Brick Mold)
If a window with exterior casing (e.g., brick mold) has been previously installed without flashing, the following instructions should be followed:
Ensure that exterior casing is sealed to the exterior sheathing or water-resistive barrier with a good quality sealant.
Cover the exterior casing with aluminum or vinyl trim sheet. This can be accomplished by using a portable field brake and bending instructions from the brake manufacturer. The trim sheet should be installed in weatherboard fashion. The bottom piece should be installed first, and each piece should overlap the piece below wherever they join.
Install rigid head flashing (i.e., drip cap) on top of the top piece of exterior casing, covering trim sheet installed in the previous step. The ends of the rigid head flashing must extend to the outer edges of the exposed legs of the side J-channels. Cut a notch on the ends of the rigid head flashing and bend them down over the sides of the exterior casing. The rigid head flashing must be sealed to the exterior sheathing and to the top of the exterior casing (Fig. 34).
J-channel is used around windows and doors to receive the siding. Follow the steps below when applying trim.
Cut and bend the tab of the top piece of J-channel down to provide flashing over the side J-channel.
Fold the bottom end of the side piece of J-channel inward at the bottom of the window, to fit over the existing J-channel to prevent water from entering under the sill.
Cut the side J-channel members longer than the height of the window or door, and notch the channel at the top.
Miter cut the free flange at a 45° angle and bend the tab down to provide flashing over the side members (Fig. 34). A similar miter and tab may be provided at the bottom of the window, depending on the sill’s condition. The J-channel should fit snug to the window.
J-Channel Over Roof Lines
Install the flashing before the J-channel to prevent water infiltration along the intersection of a roof and wall.
Keep the J-channel a minimum of 1/2” (12.7mm) from the roofing material. Chalk a straight line up the roof flashing to guide J-channel installation. Tip: You can use another J-channel laid over the shingles as a spacer to create the straight line desired.
Overlap the J-channel (lapping the upper piece over the lower piece) if it is necessary to use more than one piece. See Fig. 54 in the Vertical Siding section of this guide.
Extend the J-channel past the edge of the roof in order to ensure proper runoff. A diverter can be used; see Fig. 44 and 45 in the Horizontal Siding section of this guide.
With dark shingles, or a south or west exposure, it is recommended to either use a metal J-channel or to install the vinyl J-channel as far away from the roofing as is aesthetically acceptable, having first ensured that there is sufficient flashing behind the J-channel to prevent water infiltration.
Fasten the nail, screw, or staple that is closest to the roof line at the far end of the nail hem slot, to ensure that siding will expand away from the J- channel (Fig. 35).
NOTE: Vinyl J-channels should not be in direct contact with roofing shingles, since the shingles may transfer enough heat to the vinyl J-channel to cause its distortion.
Gable and Trim
Before applying siding to the gables, the J-channel should be installed to receive the siding at the gable ends (Fig. 36):
Where the left and right sections meet at the gable peak, let one of the sections butt into the peak with the other section overlapping.
A miter cut should be made on the face flange of this piece for better appearance.
Fasten the J-channel every 8” to 12” (203mm to 305mm).
If more than one length of J-channel is required to span a wall surface, be sure to overlap the channels by 3/4” (19mm). See Fig. 54 in the Vertical Siding section of this guide.