I have a great article I keep bookmarked on the subject:
Roof Certifications and Roof Inspections
From Elizabeth Weintraub,
Your Guide to Home Buying / Selling. (About.com)
(Please note: this quote is truncated into a short blurb to illustrate an answer to your question.)
Roof certifications are separate from a home inspection. Home inspectors, for the most part, do not perform thorough roof inspections. Instead, roofing inspectors climb up on the roof and issue reports on:
* Possible movement
* Condition of roofing materials
* Ridges, caps and drip edges
* Soundness of drains, downspouts, and gutters
* Flashing around roof pipes, chimneys, vents, valleys and mounting of HVAC units
If the roof does not require repairs, the roofing company will then estimate the remaining years of life for a roof and certify its inspection. The certification is good for two to five years, depending on local custom.
If the roof requires repairs, after the repairs are performed, the roofing company will then issue the roof certification.
You can read the entire article (which gives a very clear explanation in general) by clicking the Web References link below.
FYI: A number of buyers have stipulated this as part of the contingencies of their contracts (e.g. Subject To: appraisal, inspection, engineer's report, roof certification, mortgage, etc. ). There are a lot of stips a buyer and seller can insist upon to include in a binder and real estate sales contract to close a deal. Contracts should always be reviewed carefully before they are signed. Regards, C. ( http://www.TannStarr.com