In recent years there has been a trend away from traditional attic ventilation by many US home builders.

Wood frame homes traditionally had either gable vents in end walls or roof vents combined with soffit vents to allow attic ventilation.

Today, many builders are leaving gable vents off their homes and are instead relying on ridge vents only. 

In many other homes, vinyl siding installers are covering gable vents with siding or replacing large capacity wood vents with smaller capacity vinyl molded vents.

Ridge vents are good, but are the enough? 

In my opinion, NO.

Ridge vents that are clogged with dust,  covered with snow or ice, or simply not large enough to adequately ventilate large attics will lead to condensation problems.

Moisture is constantly flowing upward from your living areas to the attic,  If it cannot escape the attic, it will condense on the coolest surface around, the inside of the roof sheathing.

Condensation on inside of roof sheathing will cause problems such as  mold, mildew,  and most importantly it will shorten the useful life of sheathing and shingles.

In addition to moisture problems,  inadequate ventilation can lead to extreme temperatures which will also cup and damage shingles, warp boards, and damage anything stored in the attic..

Consider adding gable vents to your attic or gable along with ridge and soffit vents to make sure you are properly venting your attic.

Check out ebay auctions for vents, gable vents, louvers, etc and avoid condensation and high heat problems.