This story shows how to install ridge vents.
Ridge and roof vents are easier to install just prior to a roofing job, but they can also be retrofitted onto an existing roof. Soffit vents can be installed anytime.
Venting goes hand in hand with insulation. Measure the thickness of your attic floor insulation (or wall and ceiling insulation, if the attic is finished) and ask your building department or a home center whether you should add more.
If you need more ventilation but don't want to cut a new hole in the roof or gable, consider adding a power vent, which can be controlled by a thermostat and/or a wall switch.
Several hours to install most venting products
Tape measure, drill, reciprocating saw, jigsaw, chalkline, circular saw, hammer and chisel, trowel
Basic carpentry and roofing
Determine how much and what type of ventilation you need. Tear off the roofing or plan to cut back shingles for the installations. Make preparations for working safely on the roof.
Soffit, roof, ridge, or gable vents; nails and screws; roofing; roofing cement
Snap chalklines on both sides of the ridge to cut a slot of the recommended size -- typically 1-1/2 inches on each side of the peak. Set a circular saw blade to cut through the sheathing without damaging the rafters below. Stop cutting about 12 inches from the end of the ridge or as recommended by the manufacturer. Finish the cut with a hammer and chisel.