How to Lay Shingles
Okay, now for the fun stuff, laying on row after row of three-tab shingles. Start at the bottom. First you will have to lay down a starter course. Create this course by cutting off the tabs and about two inches from the top of each shingle of the course. Run this course to the edge of the drip edge using three nails per shingle, one in the middle and one each about 4 inches from either side. Cutting shingles is a fairly simple process. Simply flip them over and run a utility knife along a straight-edge where you wish to make the cut. Fold the shingle back and forth once, and it should make a fairly sharp division.
The first real course will go over the top of the starter course with the tabs reaching to the edge of the starter course. Each shingle will take four nails each placed about 3/4-inch above the cutouts of each shingle. The next row should be placed so that the bottom of the tab just touches the top of the cutout of the shingle just below. When you reach the edge of a roof-line or a valley, simply make a cut as appropriate.
Stacks and vents are a special case. Using pipe flashing for vent-pipes, make sure the pipe is fit securely and that the flashing is flush with the roof. Orient the flashing so that the bottom is parallel with the run of the shingles. Run two or three courses under the flashing as shown in the illustration - to a point about half-way up the flashing. Then shingle over the top side of the flashing. It may help to think of the flashing as just another shingle (though of an odd shape). Just make sure when water flows down the slope of the roof it will not be dumped under any shingles or the flashing. I liberally use tar at this point under the flashing.
Flashing around the chimney may be the most difficult and important parts of the whole shingling process. Bend several 7-inch pieces of flashing, one each for each row of shingles that will butt up against the chimney. Have these ready; as you shingle up from the bottom interlace them between each layer from bottom to top. Prepare an apron as shown in the illustration made of sheet metal to surround the top side of the chimney where it meets the roof. This is placed just before installing the row of shingles that passes over the upper side.
You're not done with the chimney yet. Make another apron similar to the one at the top. Placing it over the shingles that were laid in front of the chimney, butt it up against the chimney, putting the corners under the side flashing. Now on the sides prepare a counterflashing which is a long sheet cut in a stair step pattern. Make sure the counterflashing is placed inside the top apron but wrapped around the outside of the corner of the lower apron. Cut and arrange your flashing so that water flowing off the chimney will not be channeled beneath the shingles. Tar the sides of the chimney where they meet the flashing.
Roofing against the base of a wall is very similar to shingling around a chimney. The difference is handling the various types of siding when installing the counterflashing. The general rule is to put the flashing on in a way that will prevent the water from breaking the impermeable barrier of the roof and the siding. For lapped siding, cut individual pieces and push them up and under successive rows and cut them off just before they reach the roof.
Continue to shingle working your way up the roof until you reach the peak. When both sides of the roof reach the top, you are ready to cap off your shingling job. Cut a number of shingles vertically into thirds so that each section contains a tab, trim the upper side of each section so that it is narrower than the tab. Beginning at the edge of the ridge, tab facing outwards, bend the shingle so that it fits snuggly on the peak. Drive two nails into the upper part. Work your way to near the middle of the ridge and do the same thing from the other side of the peak to the middle. Cut one final shingle so that it is only a tab. Nail it down on all four corners and dab the nails with tar (roofing cement).
If you have read through this site to this point, you have given most of the information you need to know to get started shingling your house. But there is one other aspect you really should read up on, safety.