A valley is where two roof slopes meet at an inside corner, and it carries more water than any other single line on a shingle roof. Rain from both slopes runs down into it, snow slides into it, and in St. Louis the freeze and thaw cycle puts a lot of ice into that one trough every winter. The shingle wrapper tells you what the shingle is. It does not tell you what the valley is. That answer lives in your roof spec, and if the spec says only "shingles, valleys included," the crew will choose for you.
This page covers the four things the spec should name for a valley: the type, the metal, the width, and the membrane underneath. It is written for a homeowner comparing bids who wants to know what to ask for before the order goes in. Keys Roofing installs Atlas and Malarkey shingles, and the valley detail depends on the shingle and the slope, so the questions below apply to any roofer on your list. For the scope itself, call the Keys office at (314) 220-2333.
Open or closed: pick the type in writing
An open valley leaves a strip of metal exposed down the center of the trough. The shingles on each slope are cut back along the valley line, and the metal carries the water. An open valley is easy to inspect because you can see the metal and its edges from the ground with binoculars, and it sheds leaves and grit better than a closed valley when the metal is kept clean.
A closed valley, sometimes called a cut valley, runs shingles across the trough with the cut edge laid over the metal. Nothing is exposed, so it looks cleaner from the curb, but the shingle edges become the water path. A woven valley interlaces shingles from both slopes. Woven valleys are common on older roofs and on some architectural shingles. Each type behaves differently in a hard rain and under ice, and each needs different metal or no metal at all.
The spec should name the type in a sentence. "Open valley with metal" and "closed cut valley" are both usable. "Valleys per manufacturer" is not, because the manufacturer's installation instructions allow more than one method and leave the choice to the installer.
Name the metal, the gauge and the finish
For an open valley, the metal is the part you will see. Write the metal type into the spec. Galvanized steel, aluminum and copper are the common choices on St. Louis roofs, and each one reacts differently to the other metals on the roof. Copper beside galvanized steel will corrode the steel over time, and aluminum does not belong against fresh concrete or mortar. If your roof has copper flashing somewhere else, the valley metal and the copper need to be checked together.
Write the gauge too. Gauge is the thickness of the sheet, and a lower number means thicker metal. A spec that says "valley metal" with no gauge leaves the thickness to whatever is on the truck that morning. Ask the roofer to write the gauge as a number, and ask whether it is the same gauge used for the other sheet metal on the job, such as the drip edge and the step flashing.
Finish matters in the sun. A painted valley metal in a color close to the shingle will look right on day one and fade on a south-facing slope. Name the finish and the color, the same way you would name the shingle shade. If the metal is bare galvanized, say so, because that is a legitimate choice with a different look and a different maintenance pattern.
Width is a number, not a guess
The width of the valley metal decides how much water it can carry before the flow reaches the edge of the metal and starts to run under the shingle cut line. A narrow valley on a large catchment, such as a long lower slope meeting a short upper one, can overflow in a heavy storm. A wider valley costs a little more metal and holds more water in the trough.
Ask for the width in inches on each side of the centerline, and ask whether it is the same on every valley on the house. Many roofs have three or four valleys of very different size. If the bid says one width for all of them, ask why. The answer is sometimes sound, since a short valley does not need what a long one does, but the bid should show that thought.
The membrane under the valley
Water that gets past the metal or the shingle cut line needs a second layer to reach. Many installers run a strip of self-adhering membrane, often called ice and water shield, under the full width of the valley before the metal goes down. St. Louis winters make this worth asking about. A valley holds snow longer than the open field of the roof, and ice that forms in the trough can push water back up under the shingle edge, with the freeze and thaw cycle working directly against the seam.
Write the membrane into the spec with its width and where it runs. "Ice and water shield in valleys" is a line item, and it should be a line item with a width. Ask whether it runs the full length of the valley and how far it extends up each slope. The material cost is small. The cost of leaving it out shows up later, as a stain on the ceiling below the valley in the first hard freeze.
What to ask before you sign
- Which valley type is on the bid, open, closed or woven, and does that apply to every valley on the house?
- What metal is the valley, and what is the gauge written as a number?
- What is the finish and color of the metal, and is it painted or bare?
- What is the width of each valley in inches, and does it vary by size?
- Is there a self-adhering membrane under the valley, what width, and how far up each slope?
- Where does any copper on the roof sit relative to the valley metal, and does the spec address the pairing?
A roofer who can answer each of these in one line has probably thought about the valley. A roofer who answers "standard" to all six has left the choice to the crew. Ask for the answers in the proposal, not only on the phone, so that the spec you sign is the spec the crew reads on the roof.
When the roof is open, the valley is one of the first places to check. Ask the crew to show the metal and the membrane before the shingles go on over them, and photograph both. A valley you can see in writing, with dated photos, is a valley you can compare later if a question comes up about what was installed.