How often a roof should be replaced really depends on the type of roof. Most roofs need to be replaced after 20 to 50 years depending on the roofing material used. While minor damage can be repaired and patched up, if the roof has become worn out and damaged in large areas it is best to replace it before you spend time, money, and effort in repairing damaged drywalls or repainting the house.
First, when looking at patching damaged areas keep in mind that this may be more expensive in the long run. Replacing shingles due to wind damage or a fallen limb is relatively easy and inexpensive. Torn or damaged shingles can be removed, and new ones can be slipped in place. The downside is that unless your roof is relatively new and you happen to have saved some spare shingles from the job, your patch job may not match the existing roof. This may not be a problem for you unless you plan on selling your house, in which case a mis-matched roof patch can be a deterrent for prospective buyers. When patching your roof it is important to ask your contractor to match the shingles as closely as possible to keep the aesthetic appeal of your home. Depending on the extent of the damage, it may be more cost effective to replace your roof since this can be done in one job versus several small jobs over time.
When to reroof depends on several variables, including the shingles’ wear and age, the climate in your area, and your home’s susceptibility to future damage. The other consideration is whether to install your new roof over the existing one or whether to tear the old one off. Again this depends on the state of the current roof (how much damage is there) and the trade-off between saving a little expense now and risking greater expense down the road, and investing the money now to save on future expenses.
There is lots of great information, advice, and tips available on roof replacement, but in the end it is important to consult a professional you can trust. Get advice on how to proceed from an experienced contractor who can help you make the right decision to minimize your cost without increasing the risk of future damage and expense down the road.