Measure the area of your roof (length x width) and divide by 100 to get the number of squares required. Then multiply this number by three to get the number of bundles of shingles required for the job. Add an additional 10-15% for spare, leaning toward the 15% if your roof has hips and valleys.

Drip edge, ice and water shield, asphalt paper, flashing, roofing nails, and hip and ridge vents will also be required. The Drip edge comes in various lengths. Measure the outside perimeter of the roof to calculate the drip edge required. asphalt paper and flashing come in roles. Use your roof square area calculation for determining your asphalt paper requirements. Calculate 2 times the length of the roof and valleys to estimate the amount of ice and water shield required.

Typically each shingle will require 4-6 roofing nails and flashing usually comes in 16" wide roles or 6x6 or 8x8 square inch steps. Step flashing is typically used around chimneys, dormers and side wall junctions. Hip and Ridge vent will vary with local building codes, however a rough estimate would be to measure the length of your roof's hip and ridges and take 75% of this figure for calculating the amount of vent required.

You should now be able to fairly accurately calculate the cost of material for roofing your home.

Installing the Drip Edge

Nail the Drip edge around the entire outside perimeter of the roof.

Apply the Ice and Water Shield Membrane and the Asphalt Paper

Apply the ice and water shield material such that it is flush with the drip edge. If the climate in your area has harsh winters and/or significant annual rainfall, add a second course of ice and water shield for added protection. You should also add the ice and water shield membrane in the valleys.

Next apply the asphalt paper to the entire roof, starting from the bottom and working towards the ridge. Make sure each course of asphalt paper overlaps the lower row by several inches (effectively shingling with the asphalt paper).

Install metal flashing

Install metal flashing in all of the valleys. Step flashing around chimneys and dormers will be added as the shingles are installed.

Installing the Shingles

Start the shingling at the bottom of the roof (or at the eaves). Lay a starter course such that the bottom edge of the shingle lines up flush with the drip edge. The starter strip is a "tabless" shingle that you make from the regular shingles using your carpenter's knife.

Lay your next course of full shingles over the first course, staggering the starter joints from the first course to prevent water penetration.

Note: Sometimes you may want to start with a full or a partial shingle at one end. In either case, you want to try to avoid small shingle pieces at the far end of the roof. To prevent this, divide the length of the roof by the length of a full shingle and assess how much of a shingle length you want to start with. Ideally you do not want to have pieces smaller than 12".

Use a Chalk Line

To ensure your shingle courses run straight use a chalk line. Measure the finished reveal on your shingles. Usually this is about 5 inches. Then make marks every 5 inches on the gable ends of the roof. Snap a chalk line between the gable ends at each pair of marks all the way up the roof. This will ensure that you shingles run true and straight as you progress up the roof with the courses.

Vertical lines should also be snapped every 3 to 6 feet to ensure your tabs maintain alignment.

Use of Roof Jacks

After 3 or 4 courses of shingles have been installed using ladders, roof jacks may be necessary to access the upper courses. Roof jacks are steel brackets that hold planks in position for you to stand on. The roof jacks should be securely nailed through the decking and into rafters to ensure that they will support your weight.

Shingling Valleys, Chimneys, Skylights and Dormers, and Step Flashing

Shingling the valleys and installing flashing requires extra care. The shingles, typically coming from two intersecting courses when entering a valley, need to overlap each other such that no water penetration occurs.

Skylights, chimneys and dormers must be step flashed (step flashing is interleaved with each course of shingles) to ensure water is kept from penetrating the roof.

Adding the Ridge Vent and Caps

To complete the roofing project, ridge vents need to be installed. These are nailed to the top of the ridge and then capped.

The ridge cap prevents water from entering the home via the ridge vent, while still allowing the house to breath. The ridge cap is constructed out of individual shingle tabs that have their unfinished corners cut off at 45 degree angles. Each modified shingle tab, is nailed such that it overlaps the previous piece as you work your way down the length of the ridge vent.