If you are going to install shingles on a new roof, they should be on all surfaces of the roof including around the chimney, hips and valleys of the roof. Installing shingles around the chimney is particularly important, as the joins between the surface of the roof and the vertical surface of the chimney creates the ideal place for leaks to occur. The proper installation of shingles and flashing will prevent leaks from happening, saving you the trouble of reinstalling the roof before it is needed. This is well known by professional roofers. It does not however, take a professional roofer to do it correctly. Here you will find the information needed to install roof shingles around a chimney stack correctly.
Step 1 - Install the Flashing
The flashing should be bent at the appropriate angle (typically a 90 degree angle), so that the vertical part is flush against the chimney, and the horizontal part is flush against the roof. You will need to cut the flashing to the appropriate length for your chimney. Use the tin snips to cut the flashing. Make sure you wear good leather gloves when working with the flashing, as the metal edges or scrap can cause severe cuts in your hands. Nail the flashing to the chimney, but not to the roof. Use roofing cement to secure the flashing to the roof's surface. Use a silicone based caulk in any gaps between the flashing and the surface of the chimney, or in the corners of the flashing to create a water proof seal. Allow the caulk to cure a full twenty four hours before adding shingles or anything else to the area.
Step 2 - Install Shingles
Begin laying your shingle at the lowest point of the rise of the roof where the roof's surface meets the chimney stack. work up each side, and finally, install shingles across the top of the chimney. Use a hammer and roofing nails to secure the shingles. You will want to layer them similar to you would when laying shingles on the remainder of the roof, staggering them to help ensure a waterproof surface. You may need to trim, or custom cut shingles to fit around the chimney so that they blend into the remainder of the roof in an appealing manner, while maintaining the integrity of the roofing job. Shingles are easily trimmed using a utility knife. Use roofing cement on any shingles that have been cut to secure them to the surface of the roof.
Step 3 - Seal
Using the silicone caulk, fill and seal any gaps or seams, particularly in between the edges of the shingles and the flashing. Pick up and properly dispose of scraps of the flashing and shingles.