Asphalt shingles are the most popular roofing material used for residential construction in North America. Roofing and reroofing with asphalt shingles are normally done by specialty roofing contractors, but a homeowner with good skills and who is committed to working safely above the ground can tackle this job. In addition to learning basic roofing skills, you should follow these tips offered by manufacturers and industry pros.
Work Left to Right, Bottom to Top
Have a glance at any professional roofing crew in action, and you'll notice the same pattern is always used. Begin at the bottom left corner of a roof surface and work toward the right and upward from the eave line to the peak. Where several workers are installing shingles, one usually begins by installing shingles along the eave overhang, while others begin filling in the field, working from bottom to top.
Carefully Flash the Valleys and Seams
Almost 75% of roof leaks occur in valleys where two roof planes meet, or at chimneys or other roof penetrations, so be sure to install roof flashing in these areas prior to the start of the installation. Flashed open valleys may be more durable and water-resistant than blind alleys, in which the shingles overlap from one plane to the other and cover the valley. For asphalt shingles, aluminum flashings are recommended. The metal should be at least 0.019 inches thick.
If working on a roof where someone has already installed flashing, make sure it is in good condition and not leaking. When re-roofing, most pros choose to install new flashings rather than relying on the existing flashings.
Complete One Shingle Bundle Before Moving to the Next
Use up all shingles from the same bundle before using the next bundle. Colors may vary slightly between bundles, and by using up the bundles one at a time, you will avoid having different colors on the roof within the same area. If possible, make sure all your bundles are from the same manufacturing "lot," which will minimize color variations.
Check the Deck
A good roofing installation depends on a solid, firm deck of plywood sheathing or OSB (oriented strand board). Make sure the sheathing is in good shape, and if installing new sheet material, make sure it is approved for roof-decking use. If using plywood, make sure it is labeled CDX, meaning that it is construction grade plywood intended for exterior use. If using OSB, make sure it carries approval from the APA - The Engineered Wood Association.
In Dade County, Florida, and some other hurricane-prone zones, OSB is prohibited for use as a roof sheathing.
Use Full Tabs at Valleys or Rake Edges
Where possible, install three-tab shingles so that the tabs falling over metal valleys or rake edges at the side of the house are at least four inches wide. For better results, try to use full-size shingles going into a closed valley (one without metal flashing) as this can eliminate nailing too close to the centerline.
Attach Ridge Cap Shingles Correctly
Where a ridge is covered with shingles rather than a roof vent, make sure each cap shingle is attached with two nails, one on each side of the peak. Typically, 13/4 to two-inch-long nails are used on the ridge.
Use Proper Nails
Nails used to secure asphalt shingles must be intended for the purpose. The preferred attachment nails are galvanized steel or corrosion-resistant roofing nails. Be sure to verify this against local building code requirements and recommendations from the manufacturer.
Use Proper Nailing Technique
At a minimum, asphalt shingles can be attached with just four nails for each shingle, but if installing in an area prone to high winds, six nails should be used for each shingle. Asphalt shingles have a nailing line—a line of sealant material intended to bond with the next row of shingles. Your nails should be placed just below this line, not inside it or above it. To reduce the wind lift forces acting over the shingles, do not nail them too high or too low. Never nail through the sealant strip of the shingle as it might affect the water flow over the roof.
Make sure nails are driven straight, not angled so that the sharp edges of the nail heads can cut into the asphalt shingles. Make sure that all fasteners penetrate at least 3 ⁄4 inch into the wood deck or completely through the sheathing.
Store Shingles Properly
Protect shingles from the weather when stored at the job site. Covered by a plastic tarp is good; stored in a garage is even better. Do not store asphalt shingles near steam pipes, radiators, or any other source of heat.
Be Cautious With Double Layers of Roofing
Where allowed, you can save money by laying a new roof directly over the old shingles without removing the old roofing. However, this may be prohibited by code in some areas, where complete tear-off is required. And make sure the old roof is flat and in decent shape, as any flows or irregularity in the old roof will telegraph through to the new layer of shingles. And never go more than two layers thick.
Use Ice and Water Membrane Where Appropriate
An ice and water membrane is an impermeable rubberized fabric that is used to double-guard against moisture penetration. It is a good idea to use this to line valleys and the first few feet of the roof deck along eaves. And it may be mandatory in regions with freezing winter temperatures, where ice dams are a likelihood.
High Wind Considerations
In areas where high winds are likely, it is a good idea to use shingles with a reinforced nailing strip area. These strips will increase wind uplift resistance up to 110 mph. As a general guide, a minimum of four number nine 1 1/2-inch hex head screws must be used when shingles are installed in high wind areas.