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Cut your starter-course shingles if necessary. Cut five different lengths for staggering slots. Start laying courses. Butt a full shingle up against the cut shingle and nail into place. Cut the last shingle to the size you need when you reach the end of the row.

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If you are making your own starter shingles, cut the tabs off for the "starter course" (bottom row) of shingles. To prepare the tabs and lay the starter course, shorten the first starter shingle by 6 inches (or about a half of one tab). Place the glue strip at and all along the drip edge, and the rake edges as well. You will shingle over this starter course, so the bottom course will be double thickness.  Instead of cutting off all three tabs, you can also reverse the shingles for a starter course, so that the entire shingle with tabs turned upward are under your first course of shingles. With either method, putting the solid edge at the drip edge and cutting 6 inches off the length of first starter shingle prevents the slots between the tabs from lining up with the first regular course laid over the starter, thus not to expose the asphalt roofing paper through the slots of that bottom row. Nail the shingles with no tabs, such as precut Pro-Start shingles, and apply asphalt cement from a caulk gun in many dots along the drip edge under the edge, then press the tab-less shingles down onto the line of asphalt cement dots with adequate spaces between the dots. A continuous bead of asphalt could trap condensation or windblown water under the roofing at some point. To make sure you've got the right sizes to lay courses correctly, cut several sizes of shingles from the three-tab variety you purchased. Cut off one-half tab-width of the first tab to start the first course. Each cut is needed to shift the slots of the shingles on the course of shingles a 1/2 tab from aligning with the slots in shingles above and below. Keep all scrap, especially any single tabs for use on the ridge cap shingles. Make the following cuts:  Cut a half tab off for your first course shingles, Cut off a full tab for your second course shingles Cut one and a half tabs off of your third course shingles, Cut two tabs off your fourth course shingles For your fifth course, cut off half of the final tab Keep your sixth course tabs intact Nail the "cut off shingle" into place, about 6 inches from its lower edge. Hammer in one nail about 2 inches from each end of each shingle and another nail about 1 inch above each cutout. Make sure to keep nails out of the tar strip as you work. The next shingles above should cover the nails by about 1 inch vertically. Horizontally, end nails will be covered by up to about 1/2 of a tab, of the shingle(s) above. Be sure that these nails will hold the top edge of the course of shingles immediately below. Repeat this basic pattern, alternating shingles across the roof, working toward the right side, using the chalk line to keep the shingles straight horizontally. Use 4 nails per shingle and 6 nails on the prevailing windward sides of the roof, as wind resistance nailing. Some local codes require the 6 nails on all sides. You can let the excess extend off the side end of the roof and trim it down after it is nailed on, if you like. Continue this process to the 5th row, then begin the same process as the first row beginning with a full shingle, and a chalk mark. Repeat all of the way to the ridge. If it is a hip roof, allow about a tab width to overhang onto the next section of roof at the hip to help strengthen the joint there.