Installing Metal Shingles, continued
Vent stacks. I use oversized 18-inch aluminum vent flashings because the extra material provides more overlap and makes it easier to provide a waterproof installation. The first step is to form a right-angle bend at each side of the flashing to act as a barrier to wind-driven rain. If the lower edge of the vent flashing extends beyond the locking flange of the course of shingles below, we notch the corners of the flashing and form a back bend that hooks over the lower course of shingles.
If flashing isn't long enough to permit that, we bend a piece of coil stock to engage the lock, coat it with sealant, and press the flashing down over it. We then install an additional 4-foot-wide strip of underlayment on top of the flashing to act as a supplementary weather barrier. Finally, we cut the shingle or shingles around the vent stack with aviation snips and fasten them in place.
The edges of vent-stack flashings are turned up with a hand seamer to channel any wind-driven rain that gets past the surrounding shingles back to the outside.
Sometimes the vent flashing is not long enough to wrap around the bottom edge of the shingles below the stack. In that case, to effectively bond the lower edge of the vent flashing to the shingles, a site-bent piece of coil stock is hooked over the top flange of the full course below.
This is coated with sealant, and the flashing is pressed into place.
An additional sheet of underlayment adds protection. Finally, the vent flashing is covered by a notched shingle.
Our preferred sealant for this and all other flashing applications is a UV-protected terpolymer product called Solar Seal, from NPC Colored Sealants (708/681-1040, www.npcsealants.com). Once the vent flashing is in place, I like to prevent leaks between the neoprene sleeve and the pipe by inserting the nozzle of the caulking cartridge between them and squeezing out a bead of sealant all the way around.
Valley flashing. Like gable-edge trim, starter strips, and other special purpose flashings, Classic's valley flashing is fastened to the deck with clips. The central, open portion of the valley is defined by two parallel ridges or channels, depending on the style of shingle. Each border shingle is cut at the correct angle; the cut edge is bent down to create a shallow flange that laps over the ridge or engages the channel on that side of the valley.
Shingles that adjoin a valley are cut with tin snips.
A flange is formed with a hand seamer or portable 2-foot brake.
The valley flashing, like the shingles themselves, is fastened to the deck with metal clips.
Sidewall flashing. Most sidewall applications use a preformed flashing that has a vertical leg and a horizontal channel sized to accept the edges of the shingles. In reroofing applications, the lower courses of wood, vinyl, or fiber-cement siding are removed to allow the vertical leg to lie flat against the sheathing before the siding is replaced. (Ideally, the sheathing will be covered with felt or housewrap that can be lapped over the flashing. If there are signs of moisture between sheathing and siding, it may be necessary to remove the existing siding, nail up correctly lapped felt or housewrap to direct water past the flashing, and re-side.)
Like other special purpose flashings, sidewall flashing is fastened to the deck with clips; the vertical leg extends behind the siding and felt or housewrap.
In reroofing applications, wood or vinyl siding is removed to install the flashing and replaced afterward.
With three-coat stucco, the flashing channel, minus the vertical leg, is tucked into a slot cut in the stucco.
Traditional three-coat stucco calls for a different approach. We usually clip the vertical leg from the sidewall flashing and cut a slot in the stucco just wide enough to accept the remaining aluminum channel. We then apply a heavy bead of Solar Seal to the back of the cut-down flashing, push it into the slot, and fasten it to the deck with nailing clips.
With brick siding, we use a masonry blade to cut a 1/2-inch groove in the brick along a line 5 inches above the roof deck. We form a right-angle bend in the flashing, tuck it into this slot, and caulk with Solar Seal. When doing this, we run underlayment up the wall as far as the cut line to prevent the aluminum flashing from touching the masonry.
Les Deal is a remodeler in Cedar Rapids, Iowa.