This depends on the age of your roof. If your roof is relatively new you may just need to replace a few shingles. If however, your roof is near it's warranty limit you should consider replacing the whole roof.
Depends on the type of roof, climate and condition of the roof. Typical asphalt shingles have an average life of about 20-25 years.
We need to tear out a spot on our roof. How difficult is it to remove and replace roof shingles on our own?
Not often if there tarting to wear and tear you should replace them.
When a roof develops a leak often times caused by damage to a certain part of the roof ei: blistered or cracked areas on a flat roof or missing and cracked shingles on a pitched roof. Repairs should be preformed on a sunny day when the roof is dry.
Weather should be warm, (70 -80 f ) , not raining and preferably sunny.
A roof should be inspected annually but could be more than that. One should inspect his roof for damage after high winds, hail, or other events that could damage structures.
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Most hardware stores can provide great information on what you will need to replace the roof on a home. The internet is also a valuable resource, often providing instructional videos on how to complete your project.
Replace headlight bulb only when blown.
We need a grat to replace our roof it was bad then we had a hail storm.