Keeping Out Water
Keeping your home dry inside calls for covering the roof with the right materials and installing them in the right order. They must be firmly secured in such a way that fasteners are covered.
Much of the process of applying roofing is straightforward, but there are many ways to get it wrong and produce a faulty roof. Once you understand how the pieces go together, installing them will be fairly easy. If you are ever uncertain how to proceed, consult a professional roofer. A leak can cause serious and expensive damage to your home's interior, so it's worth any extra cost and effort to make sure that you are installing roofing correctly.
Flashing around a chimney is often a problem spot. If the flashing pieces are not installed tightly and correctly, water can seep in around the bricks and slowly damage the framing in the attic. In the usual arrangement, a single piece of flashing runs across and wraps around the base of the chimney. Individual pieces of step flashing at the sides are installed along with the roofing; each piece rests on top of a lower shingle and under the next higher shingle.
At the upper side of the chimney, there is usually a "cricket" -- a peaked roof that diverts water to the sides of the chimney. The cricket can be plywood covered with flashing or roofing or it can be made entirely of metal flashing.
Counterflashing pieces, which overlap the other flashing pieces, are installed last. These must be tightly sealed against the chimney brick. This is often done by cutting grooves in the mortar and bending the flashing to slip into the grooves. The tops of the flashing pieces are often sealed with mortar, then roofing cement.Eave and Rake Flashings
Eave and rake flashings make it difficult for water to seep under the roofing and underlayment, keeping the sheathing dry. Drip-edge, also called roof-edge, flashing is installed at the rake and the eaves. The best arrangement is to attach the drip edge at the eaves directly to the sheathing. The underlayment (felt or waterproof membrane) goes over the eaves flashing, then the drip edge on the rake lies over the underlayment. The roofing's starter strip and the first course of shingles overhang the drip edge by 1/2 inch.Valley Flashing
Visible valley flashing where two roofs meet is one common way to keep water flowing downward unobstructed. The flashing must be wide enough that water cannot seep under it and reach the sheathing. Attach it with cleats or nails driven at the outside edges so that only the heads capture the flashing. Nails driven through the flashing can lead to leaks. Sealing the shingle edges as shown keeps water from working its way underneath.Gutters
Gutters must be firmly attached to the eave fascia and tucked under the roofing so water will run into and not behind them. Gutters must slope so water runs to a downspout, which carries water down and away from the foundation with the use of a downspout extender (shown). Upper parts fit into lower parts so that water does not seep out at the joints. Connect the joints with screws and seal them with gutter caulk.Step Flashing
Step flashing is installed where a roof meets a side wall at an angle. Step flashing must tuck under the house's siding or be protected by a counterflashing so water cannot seep behind the top edge of the flashing. Where the roof meets the front of a wall on a level line, wide L-shape drip-edge flashing is installed so it slips under the house's siding and rests on top of the roofing. At an angled corner, a special piece of flashing should be custom-cut to make the transition. Self-adhesive flexible flashing can often be used in this situation. The house's siding should be cut at least 1/2 inch above the roof so that water cannot wick up into the siding.Overlapping Shingles
Overlapping shingles cover nails, sealing off leaks. Roof fasteners are usually covered by the shingle or tile above. The front edge of an asphalt shingle is held down with a thick dotted line of self-sealing adhesive on the shingle it rests on. Tiles and shakes are firm enough that they do not need their front edges fastened down. At the ridge and other places, you will end up with a couple of exposed nailheads. Cover these with roofing cement as shown.Flashing Around Plumbing Stacks
Flashing around plumbing stacks is installed so that the upper half is covered with roofing and part of the lower half rests on top of roofing. You can easily visualize how rainwater will run over the roofing and the flashing, rather than under them. Similar flashing arrangements are used around skylights.