Measure the length and width of the individual sections of the roof, multiplying them together to determine the area. [1] X Expert Source David BitanRoofing Contractor & Maintenance Professional Expert Interview. 14 July 2020. Add the areas of each section together, then divide by 100 to get the correct number of squares. Multiply this number by 3 to get the number of bundles you’ll need to buy.

The bottom row of shingles must hang past the edge of the roof. For a wood shingle roof you would have to cut the shingles that go on the edge to create a straight line to accommodate this.

Pry up the nails and loosening the ridge caps. It’s okay if you don’t get all the nails at first because you’ll have a chance to go back through and remove them later. Remove the metal flashing around chimneys, vents, and valleys in the roof. Flashing in the valleys will almost always be trashed especially. Some roofers will keep some of the flashing that’s in good shape but it’s probably worth junking it all when you’ve got the chance.

Use sticky back ice and water shield as underlayment where ice dams, leaf and twig dams are likely to build up, and at valleys or where the roof ends at a wall (wide metal flashing may also be used there). Install new flashing. Nail metal flashing called “drip edge” along the bottom edge of the roof deck near the gutters. You will also need rake edge flashing for the sides of the roof. Make sure to install flashing around the chimneys and walls. These types of flashing are known as step flashing and turn back flashing.

Mark from the left to right edge of the roof so the chalk line will be seen immediately above each course as a guideline. Continue to chalk additional guidelines based on the width of the shingle through at least four courses (rows) across the roof. When you are laying felt paper, make sure that the lines on the paper are running in a square pattern.

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,[6] X Research source 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.

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

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.

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.

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.

Bend single tabs (or special ridge shingles) over the ridge, beginning at the end putting a bead of asphalt under the first ridge shingle to hold down the tab. Nail it where the next ridge shingle will cover the nails about an inch horizontally and vertically.

Also apply asphalt cement over the nail heads exposed on the last ridge shingle to prevent water leaks.