You should install a metal valley on the roof. You can go to a “Double Weave” or a “California Cut” valley if you want to, but a metal valley is far nicer looking and it’s definitely more durable.
No matter what surface finish you use for a valley, the underlayment is done the same way. The Building Code calls for No. 30felt to be run down the flow line of the valley and the standard No. 15 felt laid into it from the sides. A better alternative to No. 30 felt is modified bitumen or rolled roofing.
Modified bitumen comes in a roll and is heavier and more expensive than rolled roofing. As you saw when we flashed the chimney, I prefer to use the modified bitumen.
Rolled roofing is either asphalt and fiberglass or a rubberized compound. It has a grit surface like shingles. Rolled roofing is designed as a finished roofing surface itself. It is approximately 40 inches wide and rolls out like the roofing felt. Rolled roofing is thick and tough. It won’t tear, it won’t get a hole punched in it, and it won’t fail in the valley.

Rolled roofing will seal around the shafts of nails that are driven through it. You will work harder because of the weight of the rolled roofing, but the valleys will be trouble-free. Rolled roofing is fine in place of modified bitumen, and both are much better than using No. 30 felt down the valley.

One bad thing about valleys is that, theoretically, you need to tear off and rebuild both roofs that meet at a valley at the same time. Problems occur when you are working alone and both roofs are sizeable.

It is impossible to tear off both roofs and lay them and the valley back up in one day. It is true you can do a good job of felting or papering the roofs in to “carry” them overnight. However, avoid planning on doing this routinely. If you tear off both roofs and the valley, it means you will have to leave a roof open (with bare sheathing) or protected only by the felt overnight. Tear off part of the two roofs that meet at a valley.

Leave part of each old roof in place from the bottom of the valley straight up both roofs to the ridge. Lap the new felt over the old roof 2 feet. Then the next day (or the day after that), you can tear off and replace the valley, concentrating just on the valley itself and the shingles immediately adjacent to it.

Let’s say you have “certified” good weather for a long weekend, and you have tom off both roofs and the valley. The first thing you do is unroll the rolled roofing up the valley. Let the loose end of the roll overlap the fascia board by at least 1 inch at each corner of the roll. (The center of the roll will be several inches over the end of the flow line of the valley.) Keep the roll centered over the flow line as you unroll it up the roof. If you try to run the roll down the valley, the weight of the roll will pull you down the roof. The roll is going to get away from you and go completely off the roof, possibly taking you with it. So let the loose end drop over the fascia, then keep the roll above you and push it up the roof.

Straddle the rolled roofing. Remember, it isn’t fastened (plus some modified bitumen has a very slick surface). Once you are over the ridge of the wing roof, brace the remainder of the roll against the valley coming to the ridge from the other side.

You may have to shift the rolled roofing to center it up the flow line or to smooth out ripples. Push the rolled roofing down snugly into the flow line. Nail both edges of the rolled roofing to lock it in place. Cut the bottom end of the rolled roofing to the shape of the intersecting fascia boards. Leave a 1-inch overhang over the fascia boards of both roofs leading to the valley. The rolled roofing is the backup system to catch any water that may escape the valley. You want it to carry the water beyond the face of the fascia board’. Now go back up to the cap at the top of the valley.

Drape the rolled roofing over the ridge and cut it parallel to and 6 inches beyond the ridge. When you have cut to a point opposite the top of the valley, cut the rolled roofing straight up the main roof. Make a cut back down into the roll from the cut edge to within V2 inch of the top of the ridge. This cut down to the top of the ridge will let the 6-inch overlap lie flat in the far valley. Leave this top end beyond the ridge loose (don’t nail it down) for now. Pull the remainder of the roll free and brace it out of your way. (When you have torn off the far side of the wing and the far section of the main roof, you will bring the rolled roofing up the far valley. Cut the top of the roll from the far valley the same way, and tuck it under the rolled roofing for this first side of the valley. Nail the roofing from the far valley in place over the ridge. Nail the rolled roofing you left loose at the top of this valley over that of the far valley and nail in place. This keeps the exposed edge of the overlap under the less visible metal valley.)

Hook a chalk line in the center of the flow line at the bottom of the rolled roofing. Pull it taut to the center of the flow line up at the ridge. Pop the chalk line. This is the line for the bend in the metal valley. When you felt in the main roof, continue the felt on to the far side of the rolled roofing up the valley. Cut the runs of felt just short of the flow line of the valley. Cut the felt so that the chalk line for the flow line of the valley isn’t covered by the felt. Leave the runs of felt loose over the rolled roofing up the valley. You want to avoid extra nails in this critical valley area. If it’s a breezy day, weight the loose ends of felt down with bundles. (If it’s suddenly very windy, bring the felt across one run at a time and shingle up that run of felt until you’re ready for the next run of felt.)

When you felt in the wing roof, run the felt across the rolled roofing up the valley. Cut that felt at the flow line and leave those ends loose too. At this point, you can see the backup roofing function of the felt. Any rain hitting the main roof or the wing roof will roll down the felts to the rolled roofing in the valley and be carried on beyond the fascia board.

You lay a roof from the rake toward the valley. You want maximum tab strength at the rake, but you are going to cut the shingles over the metal valley at an angle (wherever the chalk line hits). Therefore the width and size of tabs at the valley is going to be different for each course of shingles. Set the verticals to give maximum tab length at the rakes. On the main roof, you will be working from the rake to the valley, and you will be doing the same thing on the wing.

The ridge of the wing roof may be like the wing —it does not meet at the ridge of the main roof. The upper courses of shingles on the main roof will continue on over the wing without interruption. Therefore, you need to set the base line and offset line on the main roof so that the tabs have the maximum length possible at both rakes of the main roof.

If you run out of rolled roofing partway up the valley, lap the next roll 6 inches down over the roll you just finished and keep going up the valley. The lap will be slightly raised, but the metal valley and shingles will bridge over it and it won’t be visible.

If you want to be absolutely sure everything is smooth, use whole rolls on the front valleys or the valleys that are most visible from the ground. Use shorter sections of rolled roofing with any overlap ping joints on valleys that can’t be seen as well or can’t be seen at all.

A metal valley can be aluminum, enamel-coated aluminum, copper, or galvanized tin. Don’t use galvanized metal. It’s a pain to keep painting it. Copper is durable but extremely expensive. You again have the option of the .027 gauge or .019, gauge aluminum. Go with the heavier .027 gauge. The .027 aluminum will last beyond the life expectancy of the new roof and beyond the life of the overlay twenty years from now, too.

You should have the required sections of metal valley fabricated before you tear off. You don’t want to have the roof open and have to run off looking for a sheet metal shop. Aluminum is bent to the required shape in a metal brake, which is a machine that locks the metal in place and bends it along a straightedge.

I recommend (and urge) you to use 24-inch coil stock for the valleys. This comes in 50-foot coils. If you have access to an 8-foot brake uncoil 8 feet and run a nail along the straight edge of a “square” to scribe (scratch) where you want to cut the aluminum. Use metal shears to cut the line you scribed.

Measure 12 inches across the end of the aluminum and dimple it lightly at the 12-inch measurement with a punch or nail. Mark the aluminum this way at both ends. You are now ready to make the bend for the flow line in a metal brake.

You can cut a piece of cardboard to show the approximate size of the angle of the valley. Make sure you cut the cardboard so it fits when held in a position vertical to the valley. One comment about the angle that needs to go into the metal: it is better to have too little angle (too much toward being flat) bent in the metal than too much angle. With an angle that is slightly too small, you will have to push the metal down into the valley. The metal will tend to press down into the flow line of the valley once it is nailed in place. With too much angle, the legs of the metal will try to pull against the nails. With too much angle, the metal sides of the valley will bow up and away instead of pressing snugly down against the rolled roofing.

Nail: It takes some extra work to have the aluminum fabricated. I found that roofers who steered their customers away from metal valleys or refused to do a metal valley didn’t own, or have access to a metal brake.

You want each section of metal valley to overlap the one below it by 6 inches. If an 8-foot brake is used, and you have a valley that is 22 feet long, you have an ideal situation. You will have two overlaps of 6 inches each plus a 6-inch overlap of the metal over the ridge to the other side. You will need the metal section to overhang the fascia by 1 inch. To get the two lower comers to overhang 1 inch, the flow line will have to overhang 3 to 6 inches, depending on the slopes of the roof. Let’s add another 6 inches to be on the safe side. 22′ + 6″ + 6″ + 6″ + 6″ = 24′, so 3 8-foot sections are exactly right.

However, suppose the valley is 19 feet and an 8-foot brake is the maximum length available. The nicest looking way to divide the metal is to have equal sized sections of metal showing up a valley. In this example, we still need the 6-inch overlap over the fascia, two 6-inch overlapping joints, and the 6-inch overlap at the ridge:

19′ + 6″ + 6″ + 6″ + 6″ = 21 “, so 3 7 – foot sections are right.

The Building Code only calls for use of a 12-inch coil stock to form metal valleys. With a 12-inch stock, you will have a maximum 6-inch leg from the flow line of the valley. The Code also calls for bending an inch lip up and over both edges of the valley. This should be done with a brake, too. The bend for the flow line is made up the middle of the metal. Then the lip is bent 1 inch in from the outer edge and crimped down onto the leg of the valley using the brake. The reason for the lips along the edge is to catch and turn back windblown water being forced out of the valley. The effective leg of the valley with the 12-inch coil (minus an inch for the lip on each side) is 5 inches.

The Code also calls for the valley to be nailed down by driving the nails just outside the lips and letting the heads of the nails hold the bent edge of the lip down tight. You wouldn’t want to drive a nail through these lips because water could seep down the nail shaft and ultimately cause problems.

Nail: I have seen roofers who did their 12-inch metal valleys right, and fastened the valleys by clamping the bend for the lips under the nail heads.

They then laid their shingles and drove nails all through the metal valley. The company may have had the more experienced roofer on a crew do the valleys and special work and then had someone who only knew how to pound shingles do everything else. The result was a valley that leaked — a lot.

If you use a 24-inch coil stock, you are going to have a 12-inch leg of metal from the flow line of the valley. Beneath the metal, you are going to have a 20-inch leg of rolled roofing extending from the flow line. I don’t recommend the protective lip at the edge of 20-inch metal valleys. If you have the free use of a brake and want to put a lip along each edge of the valley, that’s fine. If you’re paying a sheet metal shop, the protective lips aren’t worth the extra price on the extra wide 24-inch metal.

You may notice that the flow line of the bare wood sheathing at the valley waves and shifts. This isn’t a problem unless the flow line in the carpentry is extremely crooked. Set the lowest section of metal valley. Keep the bend for the flow line centered top and bottom on the chalk line you popped down the flow line of the rolled roofing. The metal goes over the loose ends of the runs of No. 15 felt coming across the main roof and wing roof. The metal valley will lock these felts down against the rolled roofing. Hold down one side of the metal valley, keeping the flow line firmly in position. Nail the top comer of the metal of the side you are holding in position. Don’t drive the nails all the way home until you have all the metal valley sections in place.

Raise the bottom of the metal valley slightly to sight under it, and set the bend for the flow line directly over the chalk line. Nail the same side at the bottom of the valley. Now go to the other side of the valley and, holding that side down, nail it from the bottom, working up to the top.

Now lap the second metal section down 6 inches over the first, and set the flow line bend of the second piece over the flow line bend at the top of the first piece. Nail the bottom comer of the second piece. Check the alignment of the bend by sighting underneath to the chalk line. (Or actually run the chalk line itself up from the bottom of the flow line of the first piece of metal valley.) Shift the top or the second piece of metal until this line is perfectly straight.

Repeat the process with the third section and let it overlap the ridge by 6 inches. Now get on the ground and sight up the valley. Is the flow line perfectly straight? It should be. If it’s not, something has slipped. Since the nails aren’t driven home, you can pull the metal loose easily. One thing: If you pull a nail loose and shift the metal, go ahead and move the metal clear and drive the nail back in the hole in the rolled roofing. The material will seal around the nail. After you have shifted the metal, use a new nail to secure it. Now finish nailing the metal sections in position. A nail every foot along the edges is sufficient. Valleys aren’t subject to violent wind uplift the way rakes and caps are.

Measure vertically up the main roof from the edge of valley. Mark the courses 10V2, 5 “, 5 “, etc. If you tore off the main roof in stages and did the valley last drive nails in the felt at the tops of the shingles, where you stopped laying the roof. Hook a nail clip and pull a chalk line across the new course marks.

Pop course lines over to the flow line of the valley. Lay shingles completely across the flow line. As you continue each course, remember to nail down the ends of the shingles you left loose. Stop nailing the shingles down when you reach the edge of the metal. Just let the shingles lie across the valley.

Occasionally, you are going to lay a shingle that just barely reaches out onto the metal valley. When this happens, cut off the last tab of the last full shingle you laid. Start to cut at the center of the keyway.

Don’t try to make the cut exactly straight up the shingle; otherwise you will have to come back and trim the cut again. Angle the cut back just slightly toward the center of the shingle. Place another whole shingle in the place of the cut tab and nail the end of the whole shingle in place, keeping the nails out of the metal. This step eliminates small, weak slivers of shingles at the valley.

Lay the main roof on up until the valley is completely overlapped with shingles. At the bottom of the valley, use a tape to measure back into the main roof 3 inches. Hold the tape against the main roof on a line perpendicular to the flow line. Notch the bottom shingles at 3 inches and hook a chalk line in the notch. Sight an imaginary line that is 11 inches down (6″ cap + 5” course) from the ridge line of the wing to the corresponding course you just laid on the main roof. Gradually trim a notch in the exposed portion of shingle beneath that imaginary line.

Keep trimming the shingle until the end of the notch is 3 inches (perpendicular) from the flow line of the metal valley beneath. You get this measurement by running a tape through the notch until the end of the tape is at the flow line underneath the overlapping shingles. Hold the chalk line at the end of the 3-inch notch and pop the line.

Starting at the top cut slowly  and smoothly down this chalk line. Keep the hook blade perpendicular to the face of the metal underneath.

Trim the remnants to make cap pieces. Cut the cap pieces over a section of old roof. You don’t want any slashes or scuffs in the new shingles. Store the cap pieces and throw the scrap away. Sweep down the new roof and valley if a lot of grit has accumulated. Now finish roofing the wing and repeat the process of cutting the valley.


Tear off the other side of the main roof beyond the wing. If the main roof extends for some distance on the other side of the wing, tear off from the far rake back to within 4 feet of the valley on the far side of the wing. Felt in as you did before, overlapping the felt toward the old valley temporarily left in place.

Now you need to check and see if the fascia locations on the main roof are the same on both sides of the wing. Select a course that will extend uninterrupted from the main roof beyond the wing. There are two ways to do this.

You can use the first method if the main roof is square and has a straight bottom (or fascia) extending beyond both sides of the wing you need to cross. Measure from the fascia to the top edge of the course you will carry across the top of the wing. Now take the same measurement from the far fascia up the rake of the section of main roof on the other side of the wing. Make a mark for the top of the course at the far rake and drive a nail at the mark.

Hook the chalk line and pop a line to the top of the course you will carry across. Go to the rake you started the main roof from and sight down the top of the course of shingles. Does the chalk line continue on a straight line with the completed course of shingles? If the chalk line is straight with the course, you are in good shape. Double-check the distance from the top of the course to the ridge and from the chalk line at the far rake up to the ridge. If the distance to the ridge is the same, the main roof is square.

You can mark the horizontal courses on up from the fascia board on the other side of the wing in the normal manner, and you know they will meet properly with the courses coming over the wing. Pop chalk lines for the horizontal courses.

When you get above the top of the wing roof, extend a chalk line from the measurements or nails along the far rake back to the top of the shingles of the courses coming over the top of the wing roof. If the main roof goes down to a point (no fascia) on the far side of the wing, you will extend the course line across the top of the wing. Drive a nail at the top of the course, keeping the nail back 10 or 15 feet from the last shingle you laid in the course.

Hook the chalk line to the nail and line it up with the chalk line for the course to come across. If you have already laid the shingles to the wing, pull the chalk line tight over the wing, keeping it lined up with the top of the course of shingles you are carrying over. Pop the line. Go to the original rake and sight along the top of the course. Is the chalk line straight with the course? Good! You’re ready to go.

If the chalk line moved up or dropped from the line the completed course was following, the main roof is not square. The fascia on the partial roof on the other side of the wing may be set differently than the fascia on the first portion of the main roof. In that case, set the chalk line straight with the top of the course of shingle you are going to carry over the wing. That’s right, I finally said, “Eyeball it.” Pop a new chalk line for the top of the course. Check it from the far rake and if it looks straight, measure from this final course line down the partial roof to set horizontal courses every 5 inches.

If the fascia on the partial roof is off just a few inches, you will have to make adjustments in the height of several courses of shingles.

If the partial main roof on the other side of the wing drops down to a point in the far valley of the wing, you have no fascia from which to measure horizontal courses. That’s no problem. Again, in a case like that, you would measure 5-inch courses down the roof from the top of the course you carried across the wing.


Now the only problem is the base and offset lines. Nail the courses on over the wing roof. The first course to come uninterrupted over the wing has to be nailed high. “Nailing high” means nailing the shingle not just below the self-sealing strip but up at the very top of the shingle itself.  This will let you slide a lower course in below it. Nail this course and extend it on to a point between the wing and the far rake. Leave the end of the shingle loose. Bring the next courses up across the roof, stopping them at the same location. Leave all the ends loose.

Nail above the ends of the top two courses of shingles. Measure the distance from the rake to the ends of these two courses. Take the same measurements at the fascia board and mark them. If the bottom of the partial roof is a point in a valley, pull the measurements out from the rake farther down the roof and mark them.

Pop a chalk line at these two marks, and you have the new base and offset lines for the partial roof beyond the wing. As discussed earlier, you don’t want two consecutive courses meeting at the same vertical. So you want the shingles that will slide in below the course you nailed high to fall on the vertical line opposite the line for the course which is in place and nailed high. So you need to count odd/even down the roof. Remember to start counting at the top of the shingle of the course you nailed high. Remember, the tops of two courses are under the shingle you nailed high. Because the shingle you nailed high is 12 inches tall, the next course down will be 5 inches below and the second course down will be 10 inches below the top of the course you nailed high. If the end of that shingle is on the new offset line (closest to the far rake), the top of the next shingle down will be on the base line. Count the courses down: offset/base, offset/base, offset/base. When you get to where the first course is at the fascia, let’s say the count ends on “O” for the offset line. Stop a minute!

Remember the starter course. Count one extra time for the starter course and end up on “B” the base line. The starter course begins at “B” The first course directly over the upside-down starter shingle starts on “O” the offset line.

With this system of counting alternating courses you end up either right or wrong. The chances are 50/50.1 strongly recommend you lay a shingle (but don’t nail it) for the starter course, put the first course shingle on top of it and continue placing one shingle on each vertical for each course up the roof.

When you reach the course coming across the top of the wing, the shingle for that course should butt right into the end of the course. If the end of the loose shingle you lay to check the count falls on the base line and the shingle it is supposed to butt into is on the offset line, you know there is a mistake.

Check everything again. If you have the shingles loose-laid with the starter course in place too, trust the actual shingles and reverse the shingles all the way up. If they match properly after reversing them, nail that starter course in place and start the final shingling of the partial roof. The horizontal and vertical alignment will meet perfectly, and it will look as if the lines continued uninterrupted across the main roof despite the major obstruction of the wing roof.


Many brands of shingle have cuts at the top of the shingle exactly over the middle of the tab (6 inches from the center of each key way). The cuts are there to help you with situations like this. Find the notch in the top of the first shingle and bump the end of the second shingle against the side of the notch. This should give you a perfect 6-inch offset.

The second way to do this, if the shingles aren’t notched in the top, is to measure over 6 inches from the side of one key to the corresponding side of the key of the next shingle up the roof. Keep piecing and nailing like this until you get the courses up to the base and offset lines you popped earlier. Then just lay the courses on up and tie them in. Be sure to nail down the course you nailed high and the ends you left loose.


Many roofers will carry the cuts for the sides of the metal valley all the way up and over the ridge to meet the side cuts for the valleys on the opposite side of the wing. They mastic the cuts they made in the metal and just leave it at that. It’s an approved method, but I like to carry my caps plus one course from the wing on across the top of the valley and weave the ends of the shingles in under the tabs of the shingles on the main roof.

Trim the comer off the overlap over the ridge of the wing so that the cut is 6 inches over and parallel to the ridge of the wing. Then cut back in a direction perpendicular to that cut 6 inches to the flow line bend. This will let the metal drape down into the valley on the opposite side. Nail down the top of the metal from the lesser seen valley first, then overlap it with the metal from the most visible valley. Nail the overlaps over the ridge. You will probably have to nail the ends of the metal out across the flow line of the rolled roofing to make the metal stay down. Nail the metal legs up the main roof.

Caulk or mastic the exposed cuts you made in the aluminum valley where it goes over the ridge. You have double-overlapped the shingles going over the ridge of the wing. Carry the top course of shingles on both sides across the valley and tie the ends in neatly under the tabs of the course closest to that same elevation on the main roof. If a course over lapping the valley is going to fall just short of the flow line, cut a tab off the last full shingle and add a new whole shingle where you removed the last tab. The full shingle will reach across the valley and eliminate a sliver of a tab. Start laying the caps at the far end of the wing from the valley. Carry the caps across the valley to the main roof. Shape and mold these cap pieces and nail them as needed. Water will run off the top of these shingles and on down the valley from there, so these nails won’t cause any problem. Raise the tab of the corresponding shingle on the main roof and nail the covered end of the last cap piece up under that tab.

Trim the top of the metal valleys to suit your taste. I usually went one course down from the cap piece and trimmed across the bottom of that shingle. Carrying the shingles across the way I have shown you gives the top of the valley added protection.

Mastic under the lower edge of the shingle course across,  the top of the metal valley to keep the wind from trying to raise these shingles. Then mastic the bottom edge of the tab down to the top of the shingle you cut off. If the comers of any cap pieces are tending to stick up where you tied them into the main roof, mastic under those comers and weight them down with a bundle for a couple of days until the mastic sets. The last step is to run a bead of mastic under the cut edges of the shingles to bond the shingles to the aluminum valley.

Metal valleys are the hardest to do, but they are the most durable and give the nicest finish to your home.


If you decide against metal valleys, the double weave valley is the next best choice. The rolled roofing and No. 15 felt are done the same way on a double-weave valley as for a metal valley. On all valleys, you keep the nails as far away from the flow line as possible. You double weave a valley by laying alternate courses of shingle from each roof completely across the valley and across each other.

The sequence is as follows:

1.   Lay the starter course from the main roof across the valley and on up the wing roof approximately IV2 feet. Press the shingle snugly into the flow line and nail the far end of the shingle to the wing. Keep nails away from the immediate area of the flow line of the valley.

2.   Lay the starter course from the wing roof across the starter course from the main roof and across the flow line of the valley. Hold the shingle snugly in the flow line and nail the far end of the shingle into the main roof.

3.   Lay the first course from the main roof across the starter course from the wing roof and across the flow line of the valley. Hold the shingle snugly in the flow line and nail the far end of the shingle to the wing roof.

4.   Lay the first course from the wing roof across the first course from the main roof and across the flow line of the valley. Hold the shingle snugly in the flow line and nail the far end of the shingle to the main roof.

5.   Lay the second course from the main roof across the first course from the wing roof and across the flow line of the valley. Hold the shingle snugly in the flow line and nail the far end of the shingle to the wing roof.

6.   Lay the second course from the wing roof across the valley and across the second course from the main roof and hold and nail.

7.   Lay the third course from the main roof across the valley and the second course from the wing roof and hold and nail.

8.   Lay the third course from the wing roof, etc. You get the picture. Once the double-weave is done, don’t step down in the valley. You might crack or loosen some of the shingles. A double-weave is a good fix if you are overlaying the roof and have a metal valley that has been leaking. It is also good if the old metal valley is galvanized and rusting. The double-weave will take the old valley completely out of service.

Nail: The California Cut is an acceptable installation. It’s the quickest, easiest, cheapest, and flimsiest of the three choices. I think it’s bad enough to rate a “Nan.”


T0 reuse an existing metal valley, “nest” the courses to the old shingles and let the courses run across the valley. Keep the nails in the new shingles away from the edge of the metal valley underneath the old roof. Notch V4 to 3/s inch beyond the cut edge of the old shingles and pop a chalk line. Cut the new shingles and mastic them down to the old shingles.

Covering the old shingles by V4 inch takes them completely out of service. A double-weave and California Cut are done the same way they would be on a tear-off.