Ridge vents are much easier to install because they sit on top of the roof at the peak.
Gable vents vs roof vents.
You would also have to cover up and close the gable vents because air would come in and go straight out the ridge.
Without ventilation unfinished attic spaces can end up having stagnant air.
Gable vents are usually chosen for their visual appeal but can also serve as an exhaust vent.
Keeping the roof cool in the summer and because the outside air is drier than inside air in the cold weather it keeps the roof dry.
It will run the entire length of the gable roof peak.
You merely have to climb up to the roof and place the ridge vent.
Many roofing contractors discourage using a gable vent with ridge vent and soffit vents because a gable vent interrupts the proper airflow and can cause the air current to flow perpendicular and unevenly throughout the attic.
A new roof was installed 10 years ago at which time a ridge vent was added along all ridges at the suggestion of the roofer.
They range in style from 6 inch round stainless steel vent covers that are placed in the soffit between each rafter to continuous vents that run the entire length of the soffit.
These vents are installed in the soffit the enclosed portion under the roof overhang and permit air to flow up under the roof and into the attic.
When the wind is perpendicular to the gable the cooler outside air enters the gable vent and drops to the floor of the attic before rising to exit at the other end again leaving zones of dead air right.
Installing functional gable vents can take some time as you will need to fit them into the gable end of the roof.
On a house with eaves and gable vents but no ridge vents wind perpendicular to the ridge tends to create air flow along the floor of the attic but leave hot dead air in the roof peak left.
Without any air movement temperatures in the attic soar in summer and plunge in winter.