How to Asphalt Shingle a Divided Roof

Install metal flashing and roofing paper or a similar membrane over all sections of a divided roof. Lay roofing paper horizontally along all the roof lines, overlapping layers from the top. Put an extra strip over all valleys, the depressions where two roof lines connect. Fasten roofing paper with a construction stapler. Put flashing over peaks and ridges before laying paper, so it's under the paper; install it over the paper on valleys. Fasten flashing with shingle nails and a hammer.

Put flashing and paper around any projections, such as chimneys or vents. Use specially-formed flashing on vents and other pipes. Use flashing strips bent at 90 degrees on chimneys, with barriers on the top side to divert water to the edges so it doesn't pool behind the chimney. Nail a metal drip cap on all edges where a roof line terminates. Fasten the drip caps under the roofing paper on sloped eaves, but over the paper on angled gable rake ends.

Lay a starter strip of shingles along the bottoms of all roof edges. Use special strips if the manufacturer provides them or cut the tabs off shingles with a utility knife and install those shingles upside down, with the cut edge up the roof. Put four nails in each shingle, one on each end and two in between at about the tab locations. Let the bottom of the shingle overlap the drip edge slightly.

Fold shingles over ridges and into valleys and nail them on both sides. Overlap ridge and valley shingles, so a row coming from the left side is covered by a shingle from the right, with the next row having a shingle from the right covered by one from the left. Trim overlapping edges on valleys at about a 45-degree angle about 18 inches across the valley so the shingle doesn't stick out past the top of the next one.

Treat all ridges and valleys the same, where two sloped roofs connect. Seal a straight connection -- such as a single-sloped roof to a house wall or a lower gable end to a higher one -- starting with 90-degree flashing down the roof and up the side of the wall. Put the flashing over roofing paper, with a shingle to cover the edge down the roof and siding to seal the top of the flashing.

Work around chimneys, vents and other openings, cutting shingles to fit with a utility knife. Seal all these shingles with roofing cement for extra protection. Cover peaks, on either gable or hip roofs, with special cap shingles if the manufacturer supplies them. Cut shingles into thirds -- use cut-off tabs if they were removed for a starter strip. Fold cap shingles over the peak and fasten them with one nail at the front end of the shingle on each side. Overlap them so a shingle covers the nails of the previous cap and seal nails on the last cap with roofing cement.