Open vs Closed-Cut Roof Valleys in Massachusetts

In Massachusetts, the right valley on an asphalt shingle roof is almost always an open metal valley, not a closed-cut. Closed-cut and woven valleys are legal here, but they are the configuration that ices over first, leaks first, and shows up in February after the first real thaw. The Asphalt Roofing Manufacturers Association (ARMA) tells installers to consider open metal in cold-weather work for the same reason your slate-roof grandparents already knew: bending shingles across a valley centerline in 25 degree weather cracks them, and once they crack the freeze-thaw cycle drives water under the cap on every melt.

There is a second thing almost no national how-to article will tell you. Under 780 CMR (the Massachusetts state building code, 10th edition, which adopted the 2021 IRC for residential work as of July 1, 2025), the valley is one of the spots where a self-adhered ice-and-water barrier is mandatory. The line is in IRC R905.1.2 and R905.2.8.2 as adopted. A "one-day reroof" crew that drops a layer of #15 felt in the valley and calls it done has not built a code-compliant valley, no matter how clean the bid looked.

Here is what the three valley types actually do in a Massachusetts winter, what 780 CMR requires under each one, and the four contract lines that lock in a valley that will last as long as the rest of the roof.

What is a roof valley, and why does Massachusetts care so much about it?

A valley is the trough where two roof slopes meet at an inside angle. Every dormer, every L-shape, every cross-gable house in Massachusetts has at least one. Valleys move more water per linear foot than any other section of the roof, because they collect runoff from both adjoining planes. They are also the lowest, coldest, slowest-to-clear part of the roof in a snow event.

In a Massachusetts winter you get a specific failure pattern. Snow drifts settle into the valley. Heat escaping from the conditioned attic melts the bottom layer. That meltwater hits the cold valley cap, refreezes, and forms a ridge of ice across the valley. The next thaw pushes water sideways under the shingles next to that ice ridge. That is how valleys leak, and it is why the valley needs a self-adhered membrane under it and a flashing detail that actively sheds ice rather than trapping it.

The three valley types in plain English

There are three styles you will see on Massachusetts bids, plus one you should refuse outright.

Open metal valley. The shingles on each plane stop a few inches short of the valley centerline. A continuous metal liner (copper, painted galvanized steel, painted aluminum, or stainless) runs down the trough, visible as a stripe of metal. Water hits the metal and slides straight off. Snow and ice slide off the metal faster than they slide off asphalt because metal has a different surface and a different thermal behavior. This is the configuration that survives MA winters longest.

Closed-cut valley. The shingles from one plane (usually the lower-slope side) run all the way across the valley and continue at least 12 inches up the other slope. The shingles from the second plane are then cut in a straight line about two inches off the valley centerline and seated on top. A self-adhered membrane (or a code-compliant valley liner) runs underneath. No metal is visible. This is the default an MA production crew will install if you do not specify otherwise, because it is the fastest of the three.

Woven valley. Shingles from both planes are alternated across the centerline, each course bent across the valley and lapped over the course from the opposite plane. It produces a smooth, weave-look valley with no exposed metal and no cut line. It is also the configuration that bends shingles the most, which is why ARMA flags it in cold-weather guidance.

The one to refuse: the California valley (also called a Long Island valley or lap valley). Shingles from one plane run across, then a starter shingle is laid parallel to the valley centerline and the second plane's shingles are butted against it. It is fast and cheap. It also collects debris against that starter, dams water during heavy rain, and is widely understood by inspectors as a service-life-shortening detail. It is not specifically banned in 780 CMR, but it does not give you the self-adhered underlayment path the code wants and there is no reason to accept it on a Massachusetts house.

What 780 CMR actually requires under every valley

Two separate code sections apply, and Massachusetts roofers routinely talk about one and skip the other.

R905.1.2 (ice barrier). Per the Mass.gov ice-barrier FAQ on 780 CMR, an ice barrier is required on every Massachusetts roof. It must be either two layers of underlayment cemented together or a self-adhering polymer-modified bitumen sheet (ASTM D1970). At the eave it extends from the lowest roof edge to a point at least 24 inches inside the exterior wall line. On slopes of 8:12 or steeper, the barrier also extends at least 36 inches measured along the slope from the eave. The ice barrier rule is the one homeowners hear about. It is not the only one.

R905.2.8.2 (valley flashing). This is the section most crews undershoot. As adopted in Massachusetts, R905.2.8.2 permits three valley liners for asphalt shingles.

Valley style	Code-compliant liner under it (R905.2.8.2)
Open metal valley	Corrosion-resistant metal, at least 24 inches wide, per the metal table in R905.2.8.2
Open valley with mineral-surfaced roll roofing	Two plies of mineral-surfaced roll roofing, bottom layer 18 inches, top layer at least 36 inches
Closed valley (shingles covering the valley)	One ply of smooth roll roofing at least 36 inches wide, OR self-adhering polymer-modified bitumen (ASTM D1970), OR the same metal/mineral options as the open valleys

Then there is the cold-climate kicker. The same section says that for slopes under 7:12, where the average daily January temperature is 25 F or less (most of Massachusetts in January), the metal valley flashing underlayment must be solid-cemented to the roof underlayment or self-adhering. In plain English: in MA, you do not get to staple a strip of felt under the valley and walk away. Either it is bonded to what is under it or it is a self-adhered membrane. Most reroof contracts answer that by running ice-and-water shield the full length of every valley before any shingles or metal go down. That is the right answer. The cheaper crews answer it by hoping the inspector does not look.

Why closed-cut valleys leak first in Massachusetts

Closed-cut works fine in Atlanta. The reasons it does not work as well here are climate-specific.

In a winter where the upper attic stays even slightly warm, the snow load on the roof melts from the bottom. That meltwater follows the cold valley toward the eave. With an open metal valley, the meltwater hits a smooth metal surface and exits. With a closed-cut valley, the meltwater contacts the cut edge of the upper-plane shingles. Those cut edges are not factory-sealed. They are saw-cut on site, often with a utility knife, and they wick water by capillary action. The seal strip that bonds the cut shingle to the shingle beneath it sees that water in a freeze cycle, the freeze pushes the seal apart, and the next melt cycle finds the open lap.

Now add ice damming. A typical MA ice dam forms at the eave and backs water up under the field shingles. In a closed-cut valley, the same ice that forms at the eave forms across the valley centerline, because the valley sits lower and gets less direct sun than the field. The cut line is exactly where the ice ridge sits. The water that backs up has only one path under the shingle, and it finds it.

Per ARMA's cold-weather installation guidance, woven and closed-cut valleys force the installer to bend shingles across the centerline. When the air is below freezing, asphalt shingles do not bend. They crack. The crack does not show on day one. It shows in February three winters later, when the crack has cycled enough times to open.

ARMA's published position is to consider open metal valleys in cold weather work. That is a manufacturer trade association recommending against its own most popular configuration, which is unusual and which a Massachusetts homeowner should weight accordingly.

What an open metal valley costs vs a closed-cut valley

The honest answer is "ask the contractor for the line-item difference." A closed-cut valley uses only shingles, a self-adhered membrane underneath, and labor. An open metal valley uses the same membrane, plus 24-inch-wide painted metal coil stock, plus a slightly slower install (because the metal has to be hemmed at the edges and shingles have to be cut back to a chalk line on both planes). The metal itself is the new material line.

In our experience reviewing MA reroof bids, the open metal upgrade typically adds a low-three-figure cost per valley to a residential reroof, not a per-roof step-change. On a typical Cape or Colonial with two to four valleys, that is small money against a $15,000 to $35,000 reroof. The cheaper crews will tell you open metal "isn't necessary." That is technically true (closed-cut is code-legal). It is also the same logic they use to skip the brand starter strip and the brand ridge cap, and you can read about the wind-warranty consequences of that in our Massachusetts wind warranty guide.

The numbers in this section are relative not absolute. The actual quote depends on roof complexity, metal choice (painted galvanized at the cheap end, copper at the high end), and how many valleys you have. Ask for it itemized.

Side-by-side: open metal vs closed-cut vs woven in MA

Axis	Open metal	Closed-cut	Woven
Code-compliant in MA per R905.2.8.2	Yes	Yes, if proper liner installed	Yes, but rarely current best practice
ARMA cold-weather position	Recommended for cold-weather work	Acceptable	Flagged because shingles must bend
Self-adhered ice-and-water membrane required underneath in MA	Yes (and the metal sheds water on top of it)	Yes (and it is what is actually holding water out)	Yes
Behavior under ice damming	Sheds, metal surface clears faster	Cut line is where water backs up	Lap pattern traps water in the weave
Visible material	Stripe of painted metal or copper	Shingles only, no metal	Shingles only, no metal
Common failure mode	Sealing the metal to the deck wrong at edges	Wicking at the cut edge plus freeze-thaw on the seal strip	Cracking at the bend after a few winters
Repairability when it does leak	Easiest, the metal can be re-flashed	Hard, requires opening cut shingles	Hardest, requires opening multiple courses
Typical relative cost adder over closed-cut	Low three figures per valley	Baseline	Slightly cheaper than closed-cut
Reasonable on a Cape, Islands, or coastal MA roof	Yes, strongly preferred	Marginal	Not preferred

If your house is on the Cape, the Islands, the South Coast, or anywhere with serious snow exposure (Worcester, Berkshires, North Shore), the answer almost always lands on open metal. If your house is in central MA with a simple gable and one short valley, closed-cut with a proper self-adhered liner is defensible.

Four contract lines that lock in a valley that will last

These are four lines you can put in the contract before you sign. They cost an honest roofer almost nothing.

1. "Self-adhering polymer-modified bitumen valley underlayment (ASTM D1970) shall run the full length of every valley, minimum 36 inches wide centered on the valley, installed in addition to the eave ice barrier required by 780 CMR / IRC R905.1.2."
2. "All valleys shall be installed as open metal valleys with a minimum 24-inch-wide corrosion-resistant metal liner per IRC R905.2.8.2, hemmed at both edges, and color-matched to the shingle."
3. "No California / lap-style valleys shall be permitted on this project."
4. "Field-cut shingle edges along closed-cut valleys (if used on accessory structures or detached buildings) shall be hand-sealed with manufacturer-approved asphalt roof cement per ARMA's cold-weather installation guidance."

If a contractor pushes back on lines 1 and 2, that pushback is your signal. They were planning to do less than 780 CMR already requires under one reading and less than ARMA already recommends under the other. You can use that to compare bids honestly: the cheap bid that excludes these is not the same job as the slightly more expensive bid that includes them. For the broader version of the same vetting conversation, our hiring a Massachusetts roofer guide walks the rest of it (HIC vs CSL, insurance, lien releases).

For the parallel ice-and-water rule at the eaves (which is the more famous half of R905.1.2), see our Massachusetts ice and water shield code guide. For the underlying ice-damming mechanism and how attic ventilation interacts with valleys, see our Massachusetts ice dam guide. And if you are choosing between asphalt, metal, and slate in the first place (which changes the valley conversation completely), our asphalt vs metal vs slate roofing guide is the matching piece.

Frequently asked questions

Are open valleys better than closed valleys in Massachusetts?

Yes, in almost every case. The open metal valley sheds meltwater and ice faster, does not require bending shingles across the centerline, and is easier to inspect and repair. ARMA's cold-weather guidance points contractors toward open metal valleys specifically because of the bend-and-crack failure on closed-cut and woven valleys in cold climates. Closed-cut can work in MA on a simple roof with a proper self-adhered liner, but on a complex, coastal, or heavy-snow roof it is the wrong default.

Do I need ice and water shield under my valley in MA?

Yes. 780 CMR adopts IRC R905.2.8.2, which permits self-adhered polymer-modified bitumen as a closed-valley liner, and IRC R905.1.2 requires a self-adhered (or two-layer cemented) ice barrier on every MA roof. The standard MA reroof practice is to run ice-and-water shield the full length of every valley before any shingles or open-valley metal go down. If a bid does not say that, ask why not.

What is a California valley and is it allowed on a Massachusetts roof?

A California valley (also called a Long Island valley or lap valley) is a closed-style valley where one plane's shingles run across and the second plane is butted against a starter shingle laid parallel to the centerline. It is not specifically banned in 780 CMR, but it traps debris, dams water in heavy rain, and is a known service-life-shortener. There is no reason to accept it on a Massachusetts house. Refuse it in the contract.

How long does an open metal valley last on a Massachusetts roof?

Anecdotally on our network: a properly installed painted galvanized or aluminum open valley typically outlives the field shingles, so on a 30-year architectural shingle reroof you should not need to redo the valley separately. Copper valleys routinely outlast two generations of asphalt shingles. Closed-cut valleys, when they fail, tend to fail in years 8 to 15 in MA, often well before the field shingles. Specific service-life figures are not published by the code or by ARMA, so treat ranges as roofer experience, not specification.

Can I replace just the valley if it is leaking?

Sometimes, on an open metal valley, yes. The shingles next to the valley can be lifted and the metal can be re-flashed or replaced in isolation. On a closed-cut or woven valley you almost always have to open multiple courses on both planes to get the cut shingles out cleanly, and the cost approaches a full slope re-shingle. That repairability difference is a meaningful argument for open metal at install time.

Get matched with a Massachusetts roofer who specs valleys right

Valley failures are an install problem, not a roof problem. The fix is finding a Massachusetts roofer who already prices the job to 780 CMR, who runs self-adhered membrane the full length of every valley, and who carries 24-inch metal coil stock on the truck for open valleys without acting like you are asking for something exotic.

Tell us your town and roof shape on the /get-estimate page. We will route your project to vetted roofers in your area who quote open metal valleys as the MA default and who put the self-adhered valley liner in the contract on their own. You can also browse our Massachusetts roofing directory for vetted roofers in your area.