The Dormer Cheeks Are Where a Roof Quote Gets Thin

A dormer is the small gabled box that pushes up through a sloped roof. It gives an attic room light and headroom, and it also gives water more places to get in. On a typical St. Louis story-and-a-half house, the dormer is where most of the flashing work hides, and it is where two roof quotes can look nearly identical on the first page and differ by a full day of work on the second.

What a dormer adds to the roof

Every dormer has a front face, two side walls called cheeks, a small roof of its own, and a joint where that roof meets the main slope. Each of those joints is a place where the main roof's shingles have to be woven around, not simply cut and butted. The cheeks are the part most homeowners never look at. They are vertical walls covered in siding or shingle, and water runs down them onto the main roof every time it rains.

In a freeze-thaw winter, that run-off matters more. Snow sits on the dormer roof, melts on the sunny side in February, and refreezes at the dormer eave where the gutter ends. Ice damming at that spot pushes meltwater back up under the shingles. If the dormer valleys and cheek flashing are not right, the water finds the seam first.

The three places the flashing has to work

A dormer needs flashing in three places, and a written scope should name each one.

• The valleys where the dormer roof meets the main slope. Each valley needs a metal or membrane liner, and the liner has to run under the shingles on both sides with the courses lapped in the right direction.
• The cheeks, where the side wall meets the roof surface. Step flashing, one piece per course, should go up the cheek and be tucked behind the siding above it.
• The base of the dormer front, where the wall meets the lower roof and the window or door sill. This joint gets the most attention on the day of the work, and it is the joint that most often fails first after a hailstorm.

If a quote says "flash dormer" with nothing after it, you do not yet know which of these three the roofer plans to do, or whether they plan to do them at all.

Why the dormer cheek is often a separate job

Many roofers price a dormer as a square count on the main roof plus a flat number for the small roof. That number usually covers the shingles on the dormer top and not the cheeks, because the cheeks are treated as siding work. Ask the roofer to show cheek flashing as its own line item. If it is folded into the dormer price, ask who is responsible for it if the siding has to come off to get the step flashing behind it.

Keys documents the cheeks in the photo set before tear-off starts, with a measurement of each wall's height and width, so the homeowner can see what is being replaced and what is being reused. That written record is what to ask for from any roofer, whatever the company's reputation.

The valley question

A dormer valley gets special attention on any St. Louis roof. Two sloped planes meet at a low point, and the water from both pitches runs down to that line. Metal valley liners are common, and so are woven shingle valleys. Each has a different failure pattern. A woven valley stays watertight only if the courses are laid and nailed in the right order. A metal liner stays watertight only if it is wide enough and its edges are not left exposed to wind-driven rain. A quote should say which method it uses. If the two quotes you are comparing use different valley methods, the cheaper one is not automatically the same roof.

Measuring the dormer on the quote

Square counts on a dormer quote often leave out the dormer top and count only the main roof. Ask whether the count includes the dormer roof, the cheek faces, and any shed roof over a porch that meets the dormer. Then ask for the count as a number on the page, not a rounded figure. An aerial estimate may not show the cheek walls at all, so a dormer is where screen-based estimates tend to be least accurate. If your quote came from an aerial estimate, ask the roofer to confirm the dormer measurements from photographs taken at the roof edge or from a walk-up on the ground.

What to ask before you sign

• Does the price include step flashing on both cheeks, and is it tucked behind the siding or simply applied on top?
• What liner goes in each valley, and how wide is it?
• Is the base of the dormer front getting new flashing, or is the old flashing being reused and sealed?
• Who removes and reinstalls any siding on the cheeks, and is that work in this price?
• Will the photographs show each dormer joint before it is covered?

Ask the same questions of every bidder. A roofer who answers them plainly is giving you a scope you can compare. A roofer who says the dormer is "all included" is asking you to trust a single line.

When the permit desk asks about it

Most St. Louis County municipalities require a reroof permit that describes the work at a general level, and the dormer may not appear on that paperwork at all. If the dormer is being rebuilt, reframed, or has its window changed, that is a different scope and may need a building permit rather than a roofing permit. Check with the city or county desk before the work starts, and ask the roofer whether they pull the permit or whether you do. The permit desk will tell you which form covers what.

Photos, and the first rain after the work

The dormer should be photographed twice, once before tear-off and once after the flashing is in place and before the cladding goes back over it. A roofer who documents the joints with a ruler in the frame gives you a record that will still be useful if a leak shows up in the first winter. If it rains during the work, look at the cheek and the valley the same day. Water that shows at the ceiling under a dormer usually started at one of the three joints described above, not in the middle of a shingle field.

If you want the dormer looked at before you choose a roofer, call the Keys office at (314) 220-2333 and ask that the dormer joints be included in the photographs and measurements.