Where does the water go after it leaves your roof?

The best time to learn about drainage is during a steady rain. Put on a coat, pick a corner of the house and follow the water with your eyes. Where does it leave the roof? Does it reach the gutter? Does it run down the spout, and what happens at the bottom?

Take a dated photo of any point where the water spills, pools or goes somewhere unexpected. Then send us a note for each, such as "front gutter overflows at the corner." It is an easy way to tell the roofer exactly where to begin.

Water leaves the roof at its edge. On a pitched roof that is simple, because gravity does the work. On a roof that is nearly flat, the code says a roof that does not slope to its edges needs drains at each low point, so water does not stand on it.

If you have a flat porch or addition roof, look at it a day after rain. Water still sitting there, or a dark patch where it was, is something the roofer needs to know. Mention it when you book, and add whether the water ever reaches a gutter at all.

A gutter works only if it carries water to the downspout. The Department of Energy guide asks for a drop of at least 1/16 inch for every foot of run toward the spouts. That is a small slope, and it is easy to lose when a gutter sags or a hanger lets go.

Look for water standing in a gutter between rains, or a stretch that overflows while the rest runs clear. Either one tells you the slope has gone wrong in that spot. Mark it in a photo and ask the roofer to check the run.

The guide says downspouts should end at least 5 feet from the foundation. Some end much closer, right against the wall, and the water they release has nowhere to go but down beside the house.

Measure from the end of each spout to the wall. Write the numbers down. If any is short, tell us; it is one of the simplest things for a roofer to look at, and a short spout can explain a wet wall without any problem on the roof.

Once the water leaves the spout, the ground takes over. If the ground slopes toward the house, the water goes toward the foundation. If it slopes away, the water leaves. You can see the difference after rain by looking for pooling beside the wall.

Take a photo of any wet patch at the base of the house a day after rain. A damp wall or basement is often blamed on the roof when the real cause is the path below it. Tell the roofer both, and they will treat them as separate lines.

Some houses send water from an upper roof onto a lower one, such as a main roof draining onto a porch or addition roof. That water adds to what the lower roof already has to handle, and it arrives in one stream, not spread out. If your porch roof leaks and a higher roof drains onto it, tell the roofer.

The fix may be a gutter or downspout on the upper roof, not a change to the lower one. It is a good example of why a diagnostic visit follows the water from the top, and why a repair on the visible drip can miss the point.

In cold climates gutters can freeze, and the Department of Energy guide mentions grade-level drainage, which carries roof water away along the ground, as an alternative. It describes this as something to weigh for each house, not a rule to follow everywhere.

So nobody should tell you that gutters are simply unneeded here. Ask the roofer what each option would mean for your house: where the water would land, how far from the foundation, and what changes along the eave. Ask for the reasons in writing.

A gutter full of leaves does not carry water to the spout. The water goes over the edge, onto the siding, or behind the gutter and into the wall. You will often see streaks on the siding below the run. Those streaks are a clue about where the water went, not only a cosmetic problem.

Clearing it can show you the slope problem hiding under the debris, but stay off ladders in wet or icy weather. If the gutter still holds water or overflows after it is clear, tell us which stretch.

• Where water spills, pools or lands, with a dated photo of each.
• How far each downspout ends from the foundation.
• Whether a flat roof section holds water a day after rain.
• Whether any gutter stays wet between rains.
• Whether a stain inside lines up with any of these.

Those five items let the roofer trace the water from edge to ground in one pass. The drainage page lays out the visit, and the flashing page covers the wall joint.

• Re-hang a gutter run so it drops toward the downspout.
• Add a downspout where one run has too much to carry.
• Extend a spout so the water ends farther from the wall.
• Add a drain or a better route for a flat roof that holds water.
• Add a kick-out where a roof meets a taller wall.

Not every house needs all five, and some need none. The point is that each item is a small, specific change tied to a place on the path you walked, so you can see why it is there.