1. Starter shingles installed incorrectly (or not at all).
Many people make this mistake. It 's critical to lay down a "starter" shingle along the eaves; otherwise water will invade the sheathing and cause significant damage to your roof and house.
2. Improper use of nails.
Shingles can slip or blow off if they aren 't nailed correctly or if too few nails have been used. You should use at least 5 nails per shingle, and raise that minimum to six on roofs with steep grades. Check your local codes to determine if you live in a high wind area, which would require 6 nails. Better safe than sorry!
3. Improper slope.
Choosing roofing materials that aren 't made to accommodate the slope of the roof also leaves the home susceptible to water
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When laying down shingles for a roof, it 's important to make sure that air can escape from attics and ceilings. Otherwise, moisture can build up over time and weaken the shingle material prematurely.
7. Not planning for ice dams.
If you live in a cold climate, ice dams can form at the roofline and force water under the shingles if the roof isn 't insulated enough. Prevent this by putting down an ice and water product on the roof for about three feet or so to add an additional layer of protection against melting ice water.
8. Not aligning shingles correctly.
This might be the easiest way to spot a sub par roofing job. If the cutouts on three-tab shingles are not vertical and/or the butted joints aren 't on the same horizontal plane, the shingles are misaligned.
9. Safety.
Always follow safety guidelines. Roofing is considered one of most dangerous occupations because of the height of the work being done, and at times the conditions in which this work is completed in. Always check local safety guidelines, and be safe!!!!
10. Incorrect shingle exposure.
Always check the correct exposure. Most every manufacture lists the exposure on the wrappers. Incorrect exposure leaves the shingles vulnerable to collecting moisture during a driving rainstorm or being blown off if the wind speed