Whether or not you need to replace your roof depends on the type of roof, the age of roof and the condition of the roof. If you have a history of leaks or notice any visible discoloration or sagging (especially for composite shingle) then yes getting a new roof is probably a good idea regardless of if you go solar or not. Most installers will be reluctant to install on a roof that has potential liability issues in the future.
Some roofs just last longer than others. Metal roofs and certain kinds of tile roofs such as clay or cement typically have lifetime warranties. We can install on most tile roofs but the older ones typically require replacing the roof underlayment to prevent leaks.
Composite shingle roofs are the most common roofing type in America and if they have less than 10 years left in them its always a good idea to replace the roof. Some parts of the country where it is really cold or really humid it is recommended to replace the composite shingle roof before you go solar no matter the age of the roof, just because shingle roofs dont last long in those conditions. Keep in mind Solar Panels are warrantied for 25 years and we have systems installed in the 70's that are still operating today. Taking the solar panels off and replacing them in the future is always an option, in most cases the penetrations can remain in place so all that needs to be done is removing and replacing the solar panels. A skilled crew can get that done in a couple of hours.
Flat roofs or very low pitch roofs such as tar and gravel can be installed with no roof penetrations. Essentially the solar panels are just weighted down on the roof. In this case the only time the roof needs to be replaces is if it is so old and decrepit the added weight might cause the roof to collapse.
A few roof types most installers just wont touch unless you replace the roof. Slate roofs are notoriously difficult to install on, walking on them in general is not a good idea. Even with boards and carpet strewn about they are very easy to crack. Wood Shake/Shingle roofs are generally avoided as well. A common solution for Wooden roofs is to replace the section of the roof where solar panels will be installed with composite shingle. A good installer can make it look seamless.
Hope you enjoyed and thanks for reading!
Daniel Parrella
1-800-891-6168
Main@SpearheadSolar.com
www.SpearheadSolar.com/blog