What is a ridge cap, what does it do, and how is it installed?
Short answer. A ridge cap is the row of folded cap pieces that covers the peak where two roof slopes meet. It seals the top joint, covers the ridge vent, and is installed with each piece lapping the one before it, starting from the end opposite the prevailing wind.
What it does
- Seals the peak. Field shingles stop short of the ridge, leaving a gap the cap covers.
- Covers the ridge vent. On vented roofs, the cap sits on top of the vent and lets hot attic air escape while keeping rain out.
- Takes the wind first. The ridge is the most exposed line on the roof, so cap pieces are often the first to blow off in a storm.
How it is installed
- Install the ridge vent, if used, centered over the slot cut in the decking.
- Start at the end of the ridge opposite the prevailing wind, so the exposed edges face away from it. In much of Georgia, storms typically arrive from the west or southwest, but the roofer should judge the actual exposure.
- Bend each cap piece over the ridge, centered, and fasten with two nails placed where the manufacturer specifies, with nails long enough to go through the vent and into the decking.
- Lap each piece at the exposure printed on the bundle so the next piece covers the nails.
- Finish the last piece by cutting off the nailing area and face nailing, then seal the nail heads.
Hips are capped the same way, working from the bottom up. Use the ridge cap made for your shingle line; caps cut from 3 tab shingles are an older method and may not qualify for some enhanced manufacturer warranties. More on the roof's parts in roof anatomy explained and on venting in ridge vents vs box vents.