An example of a roof tying into a wall occurs when a home has a one-story wing that ties into a two story main house.
TYING IN A LEAN-TO ROOF
When a simple lean-to roof like you see on many screen porches ties into a wall, long lengths of single bend metal flashing are used. The metal should be fabricated in a metal brake. A metal brake is a machine that holds sheet metal fast and bends the metal over a straight edge. The length of the pieces of bent metal depends on the size, or working length, of the metal brake. I used an 8-foot brake, which means I could cut an 8-foot length of coil, clamp it down, and bend the entire length over a straightedge. A sheet metal shop may have brakes ranging up to 14 feet. I found that 8 feet was long enough for roofing.
If access to a brake is impossible, you can bend the metal with 2 x 4’s. Lay the metal on a work bench with the dimple marks for the bend even with the edge of the bench. Place a straight 2×4 over the metal. Line the edge of the 2 x 4 up right over the marks (and the edge of the bench) and clamp the ends of the 2 x 4 down with large C-clamps. Place a second 2×4 under the metal at the edge of the bench and raise the second 2 x 4 up, rolling the 2 x 4 to keep the surface of the 2 x 4 flush on the bending metal. (Friends can be substituted for C-clamps.)
Bending with 2 x 4’s works, but the metal brake gives a perfect bend, which adds to the finished appearance of your work. It’s worth it to go to a sheet metal shop and form the metal on a brake.
Whether you use a brake or 2 x 4’s, bend the metal to an angle slightly less than the angle you actually need. When the metal is nailed in place, its natural spring will push it down toward the shingle surface and the wall. If you make a mistake and get too great an angle, the metal tries to spring back up to that angle and pull away from the shingles and the wall.
Lay the last course of shingle right up to the wall. The leg of the metal covering over the shingles provides the protection from wind-blown rain. Naturally, this leg down the roof must extend over the keys and down a little over the finished tabs. If you are working from a narrow metal coil or the leg up the wall has to be long, you may have to force another course of shingles into the wall by cutting the tops of the shingles. (If you have a choice on lengths of legs, make the leg down the roof as long as is reasonably possible.) When, you must cut the top course, pop a horizontal course line across the tabs of the previous course. To cut a shingle, turn the shingle 180° so that the bottoms of the tabs touch the wall. Trim the top off the shingle, using the chalk line on top of the previous course of shingles as a guide. Use a hook blade to raise the shingle as you cut it; that way you won’t cut into the new roof underneath.
Trim the rakes.
The lengths of bent metal flashing should overlap each other by 6 inches. For example, if you’re lean-to roof is 18 feet rake to rake, and you have access to an 8-foot metal brake, you will need three pieces of bent flashing. You would need 19 feet of metal (18’+ 6″ + 6″ = 19′) to make the three pieces you need to flash this 18 feet. You should fabricate and install the metal so that the visible distance between the joints is the same. On an 8-foot brake, bend two pieces that are 6’6″ long and one piece that is 6 feet long. Lay a 6’6″ piece first lap it with the second 6’6″ piece, and lap over that with the 6-foot piece.
From the ground it will have the symmetrical, visual effect of three 6-foot pieces of bent metal flashing butted together. Pop a chalk line on the shingles to mark the lower edge of the bent flashing. (Your wall may bow in or out slightly, and you want the bottom edge of the metal to stay straight.) Slide the upper leg of the flashing up under the siding or skirt flashing of the wall. The end of the first piece of 6’6″ flashing should be exactly even with the edge of shingle at the rake. Run a heavy bead of mastic under the lower leg of the flashing so rain can’t blow underneath. Nail along the bottom edge of the lower leg.
Locate each nail 1 inch above the bottom edge of the lower leg of metal and center the nails over each tab. When you mastic the lower edge of the metal and nail it every foot, it’s not going anywhere. Set the second 6’6″ metal piece in place by sliding it up behind the siding or skirt flashing. Slide it until the end overlaps the end of the first piece by 6 inches. Run a bead of mastic under this overlap. This will keep rain from blowing into these horizontal joints.
If the top leg slides in behind the siding, you will have to determine what length of upper leg you want. The leg of the bent flashing you removed will give you a clue. You may have to notch the top of the upper leg around siding nails when you slide the new flashing up in behind the siding.
If you are nailing the top of metal flashing into a brick wall, you will find that mortar nails have the nasty habit of dancing around and auguring a larger hole in the metal. Mortar nails can also split and throw shards of metal if you really smack them. I always pre-drilled nail holes right through the metal and mortar. I used a mortar bit slightly smaller than the shaft of my mortar nails. Drilling made driving the mortar nail easier, and the metal trim stayed in better shape.
Caulk the top edge of the upper leg to the brick. Make sure the caulk also covers the heads of the mortar nails. At the end of the job, smooth aluminum caulk or gutter seal over the heads of the nails along the lower edge of the bent metal flashing. When that is done, the lean-to roof is flashed into the wall for the life of the new roof.
TYING IN AN UP-AND-OVER (SADDLE) ROOF
Step flashing is used to tie an up-and-over roof into a wall. I always trimmed the 2-inch leg that went up the wall, so that the 3-inch leg would extend with the shingle the 1V2 inches over the fascia board. Cut up the 2-inch leg, keeping the cut parallel to and 3/s to V2 inch from the bend in the metal. Place the 3-inch leg down on the felt and make a cut from the top of the 2-inch leg down to intercept the first cut you made. The angle of the second cut should roughly match the angle the comer of the siding makes with the surface of the roof. Cutting a piece of step in this way will let you slide the 2-inch leg down behind the siding. A part of the 3-inch leg will stick out over the edge of the fascia. I didn’t tell you how long the cut parallel to the bend should be, because this length will vary from house to house.
You may have to trim this piece of step a couple of times to make it fit. The bottom of this first piece of step should be even with the lower edge of the starter shingle. The first piece of step should also be nailed on top of the starter shingle. When you lay the shingle for the first course put another piece of step on top of it and place the bottom edge right at the top of the keys.
Immediately cover the piece of step over the starter course with another piece of step, but locate the bottom of this overlapping piece just above the self-sealing strip on the starter shingle. By doubling up the step on top of the starter shingle, you will properly maintain the required 2-inch downhill overlap for the piece of step flashing that goes just above the self-sealing strip on the second course of shingles.
The downhill overlap on all of the step flashing will be continuous from the ridge of the roof all the way down over the fascia.
“CUTTING IN” TO A WALL
It is extremely unlikely that any of the shingles will fit snugly against the vertical leg of the step flashing along the wall without being cut to the proper size.
Let’s assume you need to trim the final shingle on the starter course. Lay the final shingle in position as well as you can. Now flip the starter course shingle end over end. Put it back in its basic position and slide the end closest to the wall over until it is almost touching the wall. The tabs should still be pointing up the roof toward you: the grit side should be down toward the roof. Now locate the leading edge of the last shingle you nailed in place on the starter course. Take the hook blade and cut the shingle you flipped even with the leading edge of the last shingle you nailed. The cut section, which is farthest from the wall, is “waste”; lay that piece aside. Flip the piece you need end over end again.
The grit side should be up and the tabs should still be sticking up the roof. This piece should fit nicely in the gap you had in the starter course. To check yourself, notice that the starter course (and the rest of the courses) will continue with full 12-inch tabs all the way across the roof until you get to the final tab you had to cut to fit the last shingle into the wall.
Nail the piece of step you trimmed so that its bottom is even with the bottom edge of the starter shingle. (If you aren’t getting rid of the scrap pieces right away, keep the self-sealing strips facing up and the tape side down on the roof. Otherwise, the sun will seal the trash to the new roof, and when you pull the trash loose it will leave a melted asphalt stain.)
Lay the first course (right-side-up course) to the wall. Again, the gap won’t take a whole shingle. Spin the shingle 180 degrees. The grit side is facing up and the tabs are up the roof. Slide the end of the shingle into position against the wall and cut the shingle even with the leading edge of the last full shingle you nailed. Lay aside the cut piece farthest from the wall. Spin the shingle 180 degrees and slide it into the gap. It should fit properly, and you should have continuous 12-inch tabs right to the tab you cut. Nail this shingle in place.
Nail the doubled piece of step over this first course shingle as demonstrated. Cut in the second course and nail its piece of step in position with the bottom edge just above the self-sealing strip. Do the same up the roof with succeeding courses.
Nail: Because the base line and offset line are staggered 6 inches, some roofers cut the shingle pieces that butt in for the first and second course and use them as a pattern to precut the remaining shingles up the roof. This idea works in a perfect world, but the wall above the roof may bow in or angle out an inch or more. The neatest and most effective way to butt the shingles in is to cut the shingle for each course as you go up the roof. It takes more time to cut the shingles one course at a time, but then there isn’t a widening gap of step flashing showing off the cut ends of the shingles on up the roof.
TYING INTO A WALL ON AN OVERLAY
It is fairly common practice when overlaying a roof to butt the new shingles against a wall without weaving new step flashing in with the new shingles. Consider leaving out the new step flashing only if you have never experienced leaking beneath that section of wall. An intermittent leak, such as one that occurs only during storms with high winds, indicates a damaged, missing, or improperly over-lapping piece of step flashing. The way to correct that leak problem is to install new step flashing as you overlay the roof.
Nail: If you have experienced leaking along a wall, some roofers will try to get by using caulk or mastic to seal the new overlaid shingles to the wall. This is a lousy repair: the leak will return with amazing speed.
In preparation for overlaying the roof, you have cut the third course and exposed the bottom of an original piece of step flashing. Loosen and remove the nail in this exposed piece of step. Set two (or three, if necessary) pieces of new step flashing in place over the new starter shingle you are ready to lay.
The top piece of new step should slide 2 inches under the piece of old step flashing. Make sure the laps on the new pieces of step are all at least 2-inch downhill laps, and that the new step extends to the bottom edge of the starter shingle. Nail the pieces of new step in place. The nail in the old piece of step should go back in the original nail hole. What this additional step flashing does is kick any water running along this wall up on top of the new shingle at the fascia board. Now, you no longer depend on the old bottom shingle to turn the moisture for another twenty to twenty-five years.
Nail: It isn’t absolutely necessary to kick the step up on top of the new starter course like this. Most roofers don’t do it. They just butt the shingles to the wall all the way up with no new step flashing anywhere.
If you’ve never had a leak problem, you don’t want to start one. As you continue to lay new shingles on top of the old roof, remember the original step flashing comes out 3 inches under the old shingles.
Make sure the last nail toward the wall doesn’t go into the original step flashing. This lets the original step flashing continue to do its job undisturbed. Don’t worry about not nailing the new shingles the last 3 inches against the wall. The wall rising above this lower roof is protecting that end of the new shingles from wind uplift.
If you make a mistake and nail through the original step flashing, try not to worry about it. Chances are, it won’t leak. It’s just a better idea not to nail through it and ask for trouble.
INSUFFICIENT ROOM FOR VERTICAL LEG OF NEW STEP FLASHING
You have experienced a leak in the past, so you will install new step flashing. You get partway up the roof with the new step flashing and discover you can’t slide the vertical leg of the step flashing under the wood, aluminum, or vinyl siding of the wall.
There are a couple of tricks to try. If the siding is aluminum or vinyl, use one hand to pull the siding slightly toward you while you slip the pieces of step into place behind it with your other hand. If that doesn’t work, you may be able to tell that the piece of step is being stopped by a nail. (I think siding contractors drive a few nails down low so new step flashing can’t slide into place. They do it just to be ornery.) Rock the piece of step from one side to the other until you are sure where the siding nail is located. Take the snips and cut a small notch out of the top of the 2-inch leg of the step flashing, then slide the notched 2-inch leg around the shaft of the nail. You’re not likely to have a flood of water flowing along this wall, so the notch won’t hurt anything as long as you don’t completely do away with the leg that goes up the wall. Use your good judgment here. If you notch the step flashing all the way down to the “L” bend, you’ve broken the continuity of the step flashing, and it will probably leak.
TOO LITTLE GAP BETWEEN SIDING AND SHINGLES
A good siding man is going to keep his nails out of the way of the step flashing. He is also going to cut his siding up high enough that a roofer will have an easy time installing step flashing on an overlay.
However, there could be a sequel to this book showing “Nails” for siding contractors. Too many siding contractors cut their siding so that it is almost snug down on the shingles themselves. This makes it impossible to slide new step flashing in place when you overlay the roof.
If you have a leak along a wall and the siding is down on the shingles, you have two options. The first is to cut the old shingles in a line just off the end of the old step flashing. Be careful not to cut the “paper” or roofing felt beneath the shingles and step flashing. You can continue to get some use out of this old felt. Remove the cut pieces of shingle from the old step flashing, starting at the ridge of the roof.
Carefully pull the nails and leave the old step flashing in place. After the cut ends of the old shingles are removed from the step, shingle up the roof from the starter course, weaving the new shingles into place using the old step. Reuse the original nail holes in this old step flashing. No need to ask for trouble punching extra holes.
When you cut away the old shingles along the wall, you may discover that this gives you enough room to remove the old step flashing and install the new pieces. This is preferable to reusing the old pieces.
Either, one of these methods causes the new shingles to dip along the wall. Your new roof won’t look as good as it would have if you hadn’t been forced to cut and remove the old shingles along the wall.
If the old step flashing is galvanized, it is probably already rusting. Don’t trust it for another twenty years; it won’t make it. If the old step flashing is copper, and you are going back with copper on the valleys and other trim, reuse the copper step flashing. If the copper is in good shape, it should easily last the life of the new roof. One factor in the decision to reuse the copper is that the price of each piece of copper step is ten to fifteen times the price of the aluminum.