A New Way to Install Slate Roofs - Continued
Along the gable ends, we'll use a 1x4 or 1x6 instead of strapping, to give us good nailing in the fly rafter and to get us out over the rake trim. We then nail a rough-cut, full 1-inch-thick 1x4 on top at the outer edge, bringing the height up flush with the battens that we install on the rest of the roof. A copper L-flashing covers the top of the trim.
Before slate is installed, copper rake flashings get nailed into the strapping that runs along the gable end.
Laying out and installing the battens is probably the most critical step in a Nu-lok roof. Do this right and the rest of the job will go smoothly.
The battens get installed at 12 1/8 inches on-center. We use a layout stick — a piece of strapping or plywood drilled with holes every 12 1/8 inches — and hand-drive a series of 4d or 6d finish nails up every other piece of strapping to mark the layout lines (we just leave these in place, since they're well below the level of the slate). We drill the first hole at the bottom of the layout stick 131/4 inches from the end. Holding this at the outside edge of the fascia trim gives us a preset overhang of a couple of inches. This may vary from job to job, depending on the building's eaves details, but what's important is that the battens are spaced regularly at 121/8 inches up the roof.
The metal battens are installed at 121/8 inches on-center. To speed layout, the author's crew uses layout sticks drilled with holes, then drives small finish nails at every batten location.
When final chalk lines are snapped from end to end of the roof, the nails serve as a cross-check that the overall layout is square and parallel to the eaves.
We snap lines most every course up the roof; I'd recommend snapping every line for your first job, until you're accustomed to the system. We take some extra time to make sure the initial layout lines are parallel to the eaves and square to the rake trim. If this layout is good, the rest of the roof falls into place.
We'll check the distance to the ridge to make sure we don't get left with an ugly narrow strip at the top. It's possible to fudge the courses slightly tighter by trimming the top end of the link channels. We'll do this for the top few courses if necessary to maintain a nice reveal at the cap.
We nail down the battens with 8d galvanized ring shanks, shooting right through the 18-gauge metal. The battens come in 12-foot 6-inch lengths. If we need to cut them, we've found that a Morse Metal Devil blade in a cordless circ saw works well; it doesn't spark or even heat up the steel the way a grinder does.
Getting Down to Slate
After loading the roof, installing the slate is the easy part. We typically start at the ridge and install a couple of courses there, then work outward from any valleys and hips, filling in the flat field of the roof last.
Ridge. We nail full-dimension rough-cut 1x4s along the ridge on top of the strapping, which comes flush with the battens and gives us nailing for the ridge flashing and cap slates. We use 8-foot sections of flashing, usually 24-gauge galvanized, since it's concealed. We nail the cap slates through the flashing, then seal the holes with clear Lexel. You could also step-flash the ridge.
Rough-cut 1x4s nailed on top of the strapping at the ridge serve as backers for the ridge flashing and cap slates. The author uses Lexel sealant to seal the nail holes.
Because the cap slates are rigidly fixed, we shorten the last course of slates by about 1/4 inch so they'll slide in and out a little easier (in case we need to make an adjustment, or someone ever needs to make a repair).
Valleys. We use full-size 16-by-16-inch slates at the valleys, cutting them so as to get as much coverage as possible. This eliminates small triangular pieces, which clutter up the valley and would be tricky to support. Every slate needs to have a horizontal bottom edge that rests in the clips. While the field slates usually get support from two link channels, valley slates are often supported by only a single clip on one side; the valley side nests in the valley and is held down by the course above.
Using full-size 16-by-16-inch slates for the valleys gives maximum coverage without a lot of small triangular pieces.
We also weave in 24-gauge galvanized steel counter flashings up the valley. We bend these on the ground to match the valley angle, then angle them with aviation snips on the roof to follow the bottom edge of the slates on each side of the valley. The flashings rest in the clips along with the slates. We also squirt a bead of Lexel between the slate and the metal for good measure.
Galvanized steel counter flashings supported by the slate clips supply extra water protection at the valleys.
The metal is cut with hand shears to match the horizontal course lines.
Hips. Hips are treated pretty much the same as the ridge, except for the angled cuts. We use minimum-14-inch-wide slates to avoid small pieces.
Like valley slates, hip slates are cut from full-size pieces. To provide support at the narrow edge of the triangular slate, the top of the link channels can be cut down to fit between the top batten and the wooden nailer that runs along the hip.
Starter course. There's nothing special about the starter course on a Nu-lok roof, as long as the batten layout has been done right. There's no doubling — just a single slate.
Nu-lok advertises its roof as "walkable," but as with any roof, this should be left to professionals. It's not a good idea to walk in the valleys, and wherever I walk, I use caution, try to stay flat-footed, and put my weight over the battens.
Ron Waiteruns Ron Waite Construction LLC in Pawlett, Vt.