The Field of Shingles
If your roof is older, it is possible that the leak is within the roof field. This means the expanse of your roof material. If your roof is asphalt, then you can walk around with ease. Other materials such as slate, concrete tile or clay tile may not be so forgiving. You can possibly crack by walking on it, so be careful. With regular shingles, look at the tops of the vertical knockouts. Look for missing colored granules. Look for cracks. Possibly a nail has backed itself out of the roof sheathing. Simply take your time and hunt.
A valley is a line where two roof planes intersect. Valleys can be big problems if you do not trim the shingles correctly, and of course not install valley metal, or we prefer, Ice and water shield . When you trim a shingle for a valley you end up with a chisel point on the end of the shingle. If a second cut is not made to make this point like an arrow point, then water can travel along the top of the shingle and find its way inside your house.
Head Wall Flashings
Some roofs stop at a vertical wall. A metal flashing must be in place to direct water streaming down the wall away from the stopping point of the shingles. This flashing may be behind wood siding or in front of a brick wall. The flashing should extend over the shingles at least three inches. If the wall is brick or other masonry, the flashing must bend and extend one inch into a mortar joint. Tar, caulk or roofing cement should never be used in conjunction with these materials. If you see them, it is a sign that someone tried to patch a leak!
Wall Step Flashing
Some roof leaks happen at step flashings. You find these flashings where a roof climbs alongside a vertical wall. As each row of shingles is laid, a step flashing is installed over the shingle next to the wall. Part of the flashing turns up on the wall and the other portion gets covered by the next row of shingles. Look for rust or holes in these flashings. In reality, if all is well, you will be able to see only the smallest portion of these flashings.
The source of many a leaks! Chimneys contain four different types of flashing. All must be right or you will have a leak. Plus, the counter flashing that goes into the brick mortar joint must be right. A hairline crack above the flashing can allow vast amounts of water to run behind the flashings. Look for soldered corners of flashing that might have broken or have holes. Do not use caulk to repair these flashings!
Plumbing Vent Flashings
Newer vent flashings are a concern of mine. Many of these incorporate a rubber seal with an aluminum flashing. The rubber can fail in as little as 10 to 15 years. Look for cracked rubber around the plumbing pipe. The flashing should dive up and under the shingles that extend up roof from the middle of the plumbing vent. The bottom half of the flashing should be exposed and actually cover the shingles.
Furnace or B-Vent Flashing
These flashings are basically identical to plumbing vent flashings. However, they sometimes have a metal storm collar. These simply fit tightly around the vertical pipe that exits the roof. If they become loose, the storm collars can cause leaks.
Wind Blown Rain Leaks
Wind driven rain can also be a major problem. Once again, you could actually have a good roof and wind will drive water up and under your roofing materials. The only lines of defense are tar paper and the ice and water shield membranes. If you have metal valleys, you may want to hem the edges. This means that the hidden edges of the valley actual have a 180 degree bend. This creates a channel that directs wind blown rain back to the bottom of the valley. Don’t underestimate the power of a 70 mph sustained wind-driven rain.
Non-Roof Leaks !
Sometimes you think you have a roof leak when in fact the roof is fine. Attic condensation is a prime example. High humidity can cause condensation and “rain” to fall in your attic. It can also make the underside of the roof sheathing look wet. You think you have a leak instead.Chimney crowns can develop cracks. The inside surface of the chimney gets discolored or the plaster bubbles. You think a roof leak is the cause.Siding can be missing above a roof. This can cause water to enter behind head flashings.