How to Install Roof Shingles Where the Roof Lines Meet

Install metal flashing at peaks and valleys where two roofs intersect. Nail bent metal flashing with a hammer and flashing nails on both sides of a roof peak or on both edges down a valley. Place nails on the flashing edge away from the joint. Use a thick, waterproof membrane as an alternative on valleys, where two roofs come together. Pushing the flashing or membrane solidly into the valley seals it and peak flashing is secure on both sides.

Cover the entire roof with felt underlayment or similar waterproofing. Install it in layers. Overlap the layers at peaks and valleys by about 6 inches, so that underlayment seams are to the peak’s side or valley, and not in the center. Fasten it with a construction stapler along the outside edges.

Install shingles on a peak one of two ways. Run shingles up to the peak connection on both sides of the roof and install special cap shingles over the peak, extending down on both sides of the roof. Not all shingle manufacturers supply special caps. Cut regular three-tab shingles into 12-by-12-inch sections with a utility knife or shears as an alternative, and then bend those shingles over the top, nailing them in place on both sides. Nail caps in either case so that the next cap covers the nails in the previous one and seal nails on the last cap with roofing cement.

Run shingles on one roof side to a valley where two roof lines connect. Extend these shingles at least a foot onto the adjoining roof, bending them into the valley. Nail the extended ends to the other side at least 6 inches from the valley and 1 inch from the shingle’s bottom. Snap a chalk line down the valley 2 inches into the unroofed side as a guide for joining abutting shingles.

Shingle the roof’s other half up to the start of the other side’s overlap. Cut the new shingles with a utility knife or shears along the chalk line and slide each shingle under the other shingle overlap, so that there is no open seam. Don't place any nails in the valley itself.