Roofing Caps and Vents

The ridge of a roof is another trouble-prone area. In a severe high wind (such as a hurricane), the wind buffeting the side of a house takes the line of least resistance and races up and over the ridge of the roof. The result is that the shingles along the ridge are hit with a greater force and experience more severe pressure than the shingles anywhere else on the roof. The treatment of the ridge and laying of the cap pieces require special attention. On a complete tear-off or brand new home, everything should be double-overlapped on the ridge, starting with the roofing felt. Lap 1 foot of the felt from the rear roof over the ridge and staple it to the front sheathing. Lap 1 foot of the felt from the front roof and staple it to the felt underlayment and sheathing on the rear roof. You will overlap the tops of the courses of shingles the same way you do the felt. Let me point something out. If your front roof and rear roof have the exact same height, start the starter course on the front roof at the base line and start the starter course on the rear roof at the offset line. If you use the same measurement for the base line on the front and rear roofs, and you start both starter courses at the base line, and come up the same number of courses to the ridge, then the butted joints for the shingles you double overlap will meet exactly. If this happens, the butted joints are open every 3 feet along the ridge and the opening goes straight down to the roofing felt below. It’s true that you are going to cap over the ridge and the caps will cover the matching joints, so it will be watertight. It won’t be a problem until the cap pieces get old and crack. Then it can be a problem.


We have talked in earlier articles about trimming the overhangs over fascia boards, trimming into valleys, trimming into chimneys, and so on. Save all the whole tabs (full 12-inch widths) that you trim off and work them up as cap pieces. Cap pieces are made by laying the cut piece with the full tab on the old shingles with the shingle face up and the tab up the roof away from you. Hook the blade at the point where the straight side of the key ends and the curve for the top arc of the key begins. Cut the shingle from the key back at a slight angle toward the center of the tab. Do the same kind of cut from the other key or the half-key. You should end up with a whole 12-inch tab with straight sides and the top cut slightly back toward the center of the tab. None of the curved arc at the top of the key should remain. This is called “hip cutting” the cap pieces. Nail: Very few contractors hip cut their cap pieces. A straight cut from the center of the key to the top of the shingle is all that is required to make caps. The problem with a straight cut is that the curved top of the key always hangs out from under the finished edge of the caps and the straight cut is never really straight. The hip cut only leaves the machine-cut edge of the key showing, so the line of caps is perfectly straight. The reason a lot of contractors don’t hip cut their cap pieces is that for every key you have to make two hip cuts instead of one straight cut. In other words, the hip cut requires twice as much cutting. As you cut the caps, stack them finished side up and directly on top of each other. Remember the self sealing asphalt strips can bond the cap pieces together unless the caps are stacked so that the protective tape on the back of the shingles still works. Make sure that the pile is uniform and neat. Drape the pile of caps across the ridge of the roof. It will make it easier to lay them if the heat of the day has already basically molded them in the shape you want them to take. If you aren’t going to use the caps that same day, still cut and stack the caps every so often as you go along, and lock the stack of cap pieces down with an unbroken (still sealed in the paper wrapping) bundle of shingles. You don’t want a sudden high wind flinging those things at you. They act like giant flying razor blades in a high wind. Here is an example of when to cut caps. When you finish cutting one side of a metal valley, stack all the trimmed pieces that are big enough to cut for caps. Go through the small pile and cut the caps, throwing away the remaining small trimmings and trash. Stack and store the cap pieces and the job is cleaned up for you to cut the next side of the metal valley. This makes for less mess to slip on and less mess to cause a mistake. If you are roofing in the winter, keep the caps warm. If you let the caps get cold, the asphalt gets brittle. If you bend cold caps over the ridge, you can crack them. A cracked cap is nearly worthless. In cold weather, keep the caps inside in a warm spot, preferably near the furnace. Don’t bring them out side until you are actually ready to use them. Then leave them in a stack so they retain their heat until you are ready to use them. Double-overlapping the shingles in cold weather can also crack the shingles. If you are doing this work in the winter, try to save the double overlapping and capping until the warmest part of the day. Nail: Many contractors do not overlap their shingles or their roofing felt. They depend completely on the caps to protect the ridge of the roof. The only positive reason that I have heard for not double overlapping the shingles is that the caps lie flatter if there aren’t any shingles under them. This is a lame excuse for building a weak roof. We did many reroofing jobs, and many roofs we overlaid were originally done with no double overlap of the shingles beneath the caps. Some people waited too long to reroof and had suffered real water damage to the interior of their homes before reroofing. Now you may need to make a decision about the upper courses. The tabs on the shingles are 12 inches wide, so the cap pieces you’ve cut are 12 inches wide. That means when you nail them over the ridge of the roof, you will have basically a 6-inch leg of the cap coming down each side. In a perfect world, you lay the 5-inch courses right on up the roof and the top of the last course would overlap the ridge by an inch. That would leave the top of the keys 6 inches down from the ridge, and you could lay the caps in perfect position right to the top of the keys. Unfortunately, the world is an imperfect place. For instance, let’s say you have 14 inches between the bottom of the second course down the roof and the peak of the ridge. You could fill this space with another 5-inch course. Because the shingles are 12 inches high that final course of shingles will over- lap the ridge by 3 inches (14″ space – 5″ for next course = 9 ” to ridge from bottom of shingle. 12″ shingle – 9″ distance to ridge = 3″ overlap.) This is a good overlap and should be easy to nail solidly in place. However, when you nail the caps on, the 6-inch leg going down the roof will only leave 3 inches of the final course showing. (9″ distance to ridge – 6″ leg on cap = 3″) The other option would be to reduce the final course to a 4-inch course. That also works. (14″ distance to ridge – 4″ final course = 10″ to ridge. 12″ shingle -10″ to ridge = 2″ overlap) This may be a little more difficult to nail if the ridge isn’t perfectly straight or there is a large gap in the sheathing at the ridge. However, when you nail the caps on, they leave 4 inches of the final course showing. (10″ to ridge – 6″ leg of cap = 4″) In this case, whether you want a 5-inch course, a 3-inch course, then a 6-inch cap; or a 5-inch course, a 4-inch course, then a 6-inch cap is up to you. However, the second combination is less notice able. Now that you’ve decided how you want to do the courses, the next problem you face is that you’ve run out of horizontal course lines. Let’s say you decided to go with the 5″-4″-6″ cap combination. Measure up the roof 4 inches from the bottom of the last course of shingles you laid. Drive a nail at 4 inches into the last tab along the edge of the roof and hook the chalk line on it. (I know. After you pop the line, you are going to have to replace that tab. When, you get to the rest of the roof leave that last shingle off so the nail hole won’t create extra work. I apologize; it was easier to show you why to leave that shingle off than to go into a detailed explanation.) Play out the chalk line across the roof and measure up 4 inches from the bottom of the last course on the far end of the roof. Pull the line tight beneath the tape at the 4-inch mark and pop the line. Go back and remove the shingle or tab I made you ruin by driving the nail. Replace that shingle or tab. Lay the shingles, keeping the bottom edge of the shingles right on the new course line across the tabs. Don’t lay the last shingle on the front roof. You need to pop a line for the caps. I always overlapped the shingles from the rear or least visible roof first. Then I overlapped the shingles from the front. The front shingles “bridged” over the nailed “tops” of the overlapped shingles from the rear. When I nailed on my cap pieces, the caps covered the nailed “tops” of the front shingles where they overlapped to the back roof. This sequence gave the front, or more visible roof, a nicer fit and finish. Putting the last few courses in and double overlapping takes a lot more time than you would think just reading about it. If darkness or exhaustion is over taking you, the ridge of the roof is substantially sealed even without the cap pieces. Center a cap piece over the ridge of the roof where you left that last front shingle off. (The cap piece goes up and over the ridge of the roof.) Once the cap piece is centered over the ridge, drive a nail even with the bottom of the cap piece. Hook a chalk line to the nail and gently reel it out to the far rake. Center a second cap piece over the ridge at the far rake and pull a chalk line tight along the bottom of the cap piece. Remember, some brands have a small slit at the top of the shingle right in the middle of the tab, which is now the cap piece. Use it as a guide to center the two cap pieces. Pop the line. You want the line you will use to lay the caps on the front roof. The line in the front will be perfectly straight. If there is any sagging or variation due to an uneven ridge line, let it be to the rear where it won’t be seen. The prevailing wind in our area is from the west. Most of our storms seem to blow from the west. On a house with a ridge line that ran east and west, I always started capping on the east end. This left the upraised or exposed end of the cap piece facing the direction away from the prevailing winds. The next most likely direction of severe winds for us is from the south, so on a ridge with a north/south orientation, I would start capping on the north end. Center the cap piece over the ridge of the roof with the tab going up and over the ridge. Line up what would have been the bottom of the tab with the cuts on the rakes, and then line up what was formerly the side of the key with the chalk line for the caps. Nail the front leg of the cap just toward the exposed surface from the self-sealing strip. This action tends to roll up the self-sealing strip, so the exposed edge of the next cap will seal down more completely to it. Mold the cap down securely and nail the rear leg down. Now nail the two comers at what was the top of the shingle. You have the first cap piece in place. Now center the second cap piece over the ridge, leaving the 5-inch tab of the first piece exposed. Nail it just as you did the first piece. The Building Code calls for each cap piece to have four fasteners, whether you use nails or staples. I put four nails in each cap piece. Then when I over lapped the next piece, the two nails closest to the exposed tab portion of the second piece also went through the first cap piece. This means each cap piece was held in place with six nails. Continue laying caps across the roof until you get to the far end. Now if you keep going, you are going to have the upper end of the shingle exposed at the end, instead of the tab portion with the finished grit on it. Keep going the way you have and let the top of the last cap stick out over the cut rake by 2 inches. Nail the cap piece in place. Cut off the overhanging portion even with the rake cuts. Now cut off the top 4 inches of a cap piece and turn this piece to run the other way, keeping the bottom of the tab portion even with the rake cuts. Nail this piece down with two nails, again placing them just toward the tab from the self-sealing strip. Now we need a “locking cap.” Cut the exposed part of the tab off a cap piece. Start a cut where the top of the key would have been and cut straight across the tab to where the top of the opposite key would have been. You should end up with the exposed grit covered piece measuring 5″ x 12″. Center this rectangular piece over the overlapping tops of the last two cap pieces you laid. It will cover them nicely and give the roof a finished look. Nail down each corner of this rectangular piece. (Use aluminum nails.) Cut another rectangular piece and go to the far end of the ridge. Center it over the exposed edge of the second cap piece and nail the rectangle down at all four corners. You should use aluminum nails on these, but a galvanized nail is all right if you put a dab of mastic or caulk over each nail head. If you have been able to get a silicone caulk with a color similar to the shingles, that’s even better. The caps are now securely locked at each end of the ridge. If you do the caps this way, and your house goes through a hurricane, you will find that a tremendous amount of other damage will have occurred before the storm starts to bother the caps on the roof. It will take a history-making storm to damage caps done the way we did these. Nail: I have never seen a roofer in our area put more than two fasteners in each cap piece. Also, most of them just continue their cap pieces on to the end rather than turning the last one and installing “locking caps.”


In recent years, a large number of homeowners have installed ridge vents when they reroofed their homes. To install a ridge vent, you basically cut a 1- to 2-inch slot through the shingles and sheathing along the ridge of the roof. You cover the slot with a ridge vent unit, which is, in effect, a roof over a roof. Convection currents through the attic carry the hot air out through the slot you have cut in the ridge of the roof and through the tiny louvered vents on the underside of the top section of the ridge vent unit Ridge vents carry a lot of heat out of the attic, and they are reasonably durable. However, I’m not convinced that they will hold up well in severe storms. You install a ridge vent by continuing up the roof just as if you were going to double overlap the shingles. However, now you will want to measure how far the legs of the particular ridge vent will go down the roof from the ridge. Adjust the last couple of courses into the ridge accordingly, but remember, at the ends of the roof you are going back to the double overlap and caps. Let’s say you want to use ridge vents on a section of roof where the ridge is 30 feet long. Ridge vents come in 10-foot sections, and they can be cut with a hacksaw. You decide you want to go with the installation of 20 feet of ridge vent. There are plastic, vinyl and aluminum ridge vents on the market. (You know how I feel about plastic on the roof.) Go with the aluminum. You will need to buy two 10-foot sections of ridge vent, one connector for tie the two 10-foot sections together, and two rubber ends to seal up the ends of the ridge vents. Lay the shingles up and over from the back to the front, but don’t nail down the overlap. The slot in the sheathing is supposed to be cut down right at the end of the ridge vent so the vent unit can sit right down beside the caps. On a 30-foot roof with a 20-foot ridge, the computations are: 30′ length – 20′ of ridge vent =10′ length of ridge that will need cap pieces You generally are going to want the ridge vent centered on a roof, so you divide the remaining capped length in half: 1072 = 5’ Measure 5 feet from the end of the roof: this is where you will start the ridge vent. As I said, I’m not sure I trust ridge vents. A straight cut, even with plenty of caulk and mastic, is most likely going to cause a problem eventually. We should leave another foot of double overlapped shingle under the end of the ridge vent just in case. So, mark 6 feet from each end of the ridge and cut the 18 feet (30 – 6′ – 6′ = 18′) of shingles down 1 inch from the ridge line on both the front and back roofs. (A chalk line will help keep this cut straight.) Overlap and nail the 6 feet of shingles located at each end of the ridge cap placement. Now lay the courses up the front roof. Again, cut the 18 feet where the ridge cap will be and then overlap the 6 feet of shingles at each end onto the rear and nail them down to form the double overlap on the 6-foot end sections. Many roofs have a gap in the planks or plywood at the ridge of the roof. If the gap already, there is say 3At inch, don’t bother to widen it. If the plywood is jammed right up tight along the ridge, you will need a circular saw to cut a couple of strips out of both sides. Set the saw so that the blade will cut down through the plywood sheathing without going through the 2 x 4 rafters beneath. Wear protective goggles. Chances are, you are going to hit the edge of a shingle or maybe even a hidden nail. Stuff will fly back in your face like a small explosion. Don’t be a hero and think it can’t happen to you. Keep a careful check on the depth the blade is cutting. Cutting across all the roof rafters and making them collapse is only funny if a professional stuntman does it in a movie. You should have set the depth of the saw so that the plywood slots you cut are still hanging by a thread. Knock the cut slots out with a hammer. Sweep and remove the trimmings, sawdust, and grit that have accumulated. Now run a heavy bead of mastic on the shingles below the slot you just cut. Make sure you keep this heavy bead well within the area that the base or legs of the ridge vent will rest on. Use a generous amount of mastic, but not so much that it will squeeze out down the roof below the ridge vent. Now go back to the measurement 5 feet from the end of the ridge and run a bead straight up and over the double overlapped shingles, tying it in with the parallel bead you ran on the back of the roof. Insert the rubber end in the ridge vent and set the first section of ridge vent down in the mastic. Now butt the second 10-foot section against the leading end of this first section. Mark where, the far end stops. It will be 5 feet from the far end of the roof ridge. Finish laying a bead of mastic along both the front and back of the slot and then lay a bead up and over beneath where the rubber end will be located. Set the second section of ridge vent in mastic with its end firmly butted to the first section. Come back to where you butted the ends of the two pieces of ridge vent together and run a bead of mastic up and over the top of the crack between them. Lay the connector piece up and over them, but don’t nail it yet. Sight down, the ridge vents and get them lined up straight down the ridge line. Now nail the comer nearest you, but don’t drive any of the nails down tight. (A bag of twisted shank aluminum nails should have come with each section of ridge vent.) A nail set is handy when installing most designs of ridge vent. The set will help you keep from hitting the raised flange on the outside of the unit and bending it down. Stand up and sight along the ridge again to make sure everything stayed straight. Nail the far end of that same 10-foot section where the two sections join. Go back and sight down it again to make sure it’s still straight. Now nail the far end of the second 10-foot section. Sight from there and see if both units are still straight. Go back to the center and, keeping the two sections lined up nail down the end of the second 10-foot section. Nail the center nails down snug and nail the one end of the joint piece down. Drive the nails snug at both ends. Repeat the same process on the other side of the roof. When you have the entire length of both sides snagged down tight, drive a nail in every pre-drilled nail hole in the ridge vent units. Go back to the ends and seal along the base of the rubber end pieces with mastic. (I usually covered the whole end piece with caulk.) Nail: Many roofers install ridge vents without using mastic at all. The unit’s legs going down the roof are not very long. If rain blows in under the units, it is going to drop into the home through the open slot in the roofing and sheathing. Also, I have seen cases where other roofers only drove nails in every other or every third pre-drilled nail hole and used smooth shaft galvanized roofing nails to install the unit. The first blast of high wind will take those ridge vents. Nail: Some roofers have been known to install “lookalike” ridge vents. They never cut the slot in the shingles and sheathing. The installation looks like a ridge vent, but it doesn’t ventilate anything. I don’t like ridge vents. However, this method of installing them should keep them in place and keep you high and dry. If your hands get covered with mastic, kerosene or diesel fuel will take it off.


I have run into cases where the roof was not square It’s a good idea to stop popping horizontal lines 3 or 4 feet down from the ridge and measure along each rake from the last line you popped to the center of the ridge. Let’s say you are down eight courses from the ridge line, and the distance at the left rake is 45inches. This will put you just right coming up to the ridge. Let’s be a little extreme and say the distance on the right rake is 49 inches. The right end of the courses will come into the ridge 4 inches lower than the left end. Double-check the measurements for the 5-inch courses at the left and right rakes. Make sure the chalk lines are popped correctly. Check across the final chalk line you popped. Does it fall down from the ridge continuously across the roof? We decide the carpentry on the roof is definitely out of square. We have eight courses to make up a 4-inch shortfall on the right rake. It will weaken the roof and possibly expose some of the black grit portion of the upper part of our shingles if we try to increase the height of the courses on the right. The only thing to do is decrease our measurement for the courses going up the left rake. 4″/8 courses = V21′ per course. We have to decrease our left rake measurements for the last eight courses to 472 inches, while we leave the measurement for the courses at our right rake at 5 inches. Someone looking up from the ground probably won’t detect the V2-inch variation in these last eight courses, and the top course of shingles will be even with the ridge line and the cap pieces.


Overlay the old roof until the new courses on both legs of the roof are up within a few courses of the old caps. Tear off the old caps. If the courses beneath the cap are cut at the ridge or are crooked coming to the ridge, you should consider tearing off those couple of courses, too. Nail: On an overlay, one of the first steps many roofers take is to remove the cap pieces. It is neater and easier to remove the caps first. However, if the shingle courses at the ridge aren’t double-over-lapped, the roof is open and waiting for rain. Too many roofers don’t have a roll of felt or tarps on an overlay job. They don’t have a way to seal that ridge if a sudden storm hits. It’s a better idea to tear off the old caps when the new shingles are up to the caps on both sides of the roof. Then you know the caps are going to be replaced immediately.