Open vs Closed Valleys on North Vancouver Shingle Roofs
Open vs Closed Valleys on North Vancouver Shingle Roofs
An open valley shows a strip of metal flashing down the join between two roof planes. A closed valley covers that join with shingles. On a North Vancouver asphalt shingle roof, we usually lean towards the open metal valley. The reason is the combination of heavy rain, fir needles and maple leaves, moss and the odd freeze-thaw week. Closed-cut valleys can still be done properly, and the right choice depends on your roof’s pitch, its tree cover and how the valley is built.
This guide explains how each type is put together, what the building code and Canadian trade guidance say, and how to judge a quote from a roofer.
TL;DR
- An open valley uses a metal channel with shingles trimmed back from the centreline. A closed-cut valley has shingles running across the join, with the flashing hidden underneath.
- Open valleys move water and debris along a clear channel, which is why they suit tree-lined North Shore lots and lower-pitched sections.
- Closed-cut valleys give a cleaner, uninterrupted look and can perform well when the nailing, trimming and cement details are followed exactly.
- The British Columbia Building Code sets minimum details for both: open valleys need metal at least 600 mm wide, and closed valleys are restricted on low slopes.
- Most valley leaks come from small installation details, not from the valley type itself.
Table of Contents
- Why valleys are the weak point on a North Vancouver roof
- How a closed-cut valley is built
- How an open metal valley is built
- Open vs closed valley at a glance
- Which one suits your North Vancouver roof
- Our perspective
- Installation mistakes that cause valley leaks
- Keeping valleys clear between roof jobs
- Talk to us about your valleys
- FAQ
- Sources
Why valleys are the weak point on a North Vancouver roof
A valley is where two roof planes meet at an inward angle. Every drop of rain falling on both planes ends up funnelled down that one line. On a hip-and-gable house with dormers or an addition, there can be several valleys, and each one carries more water than any other part of the roof.
That concentration matters on the North Shore. We get long wet spells in fall and winter, and many lots are surrounded by tall conifers and broadleaf trees. Needles, seeds and leaves wash into valleys and sit there. Moss follows, holding moisture against the shingles for weeks. The National Roofing Contractors Association notes that valleys are prone to debris accumulation, and that their service life is affected by snow, ice, rainfall, humidity, temperature swings and wind. It adds that the best valley configuration depends on those conditions, plus the roofing material and slope.
So the question is not which valley looks better in a brochure. It is which one keeps working on your roof, under your trees, in your weather.
How a closed-cut valley is built
In a closed-cut valley, shingles from one roof plane run right across the valley and up onto the other plane. Then the second plane’s shingles are trimmed along a line near the centre. From the street you see an unbroken field of shingles.
The Canadian Roofing Contractors Association (CRCA) lays out the method in its reference manual section on valleys. In plain language, it goes like this:
- Valley underlayment goes down first, before any shingles. The manual describes a strip about 1 m (39 in) wide with proper overlaps.
- One roof plane is shingled across the valley and at least 300 mm (12 in) onto the adjoining plane, starting on the lower-slope or lower-height plane.
- The adjoining plane is shingled up to the valley and trimmed at least 50 mm (2 in) from the centreline.
- The upper corner of each trimmed shingle is clipped 25 mm (1 in), and each end shingle is embedded in a 75 mm (3 in) strip of plastic cement.
- Nails stay at least 150 mm (6 in) from the centreline, and the shingle crossing the valley gets two nails at its end.
The strengths are clear. It is quick, tidy and sheds water well when built to that standard. Many homeowners prefer the look, especially on a visible front elevation.
The trade-off is that the water channel is underneath layers of shingle. IKO, a shingle manufacturer, says closed valleys can restrict water and debris flow compared with a metal flashing. Under heavy tree cover, that is the detail we pay closest attention to.
How an open metal valley is built
An open valley starts with the same underlayment, then adds a metal lining that stays exposed. Shingles are held back from the centre to leave a clear channel. NRCA describes it as a metal lining over valley underlayment with shingles held back from the centreline to create an unobstructed runoff channel.
The CRCA manual gives the details that separate a good open valley from a poor one:
- Corrosion-resistant metal flashing, at least 600 mm (24 in) wide, centred over the underlayment.
- Nailing along the outer edges on 300 to 450 mm (12 to 18 in) centres, without puncturing the metal itself.
- Multiple pieces overlapped 300 mm (12 in) in the direction of flow and embedded in plastic cement.
- Chalk lines snapped 100 mm (4 in) from each flashing edge, tapering inward at 10 mm per metre (1/8 in per foot) so the channel widens as it goes down.
- No shingle shorter than 300 mm (12 in) used to finish a course into the valley.
- The upper corner of each end shingle clipped 25 mm (1 in), then cemented to the flashing with a 75 mm (3 in) strip of plastic cement.
- No exposed nails along the flashing.
That last point on clipping corners is one people skip. The CRCA says failing to trim the corners can let water run along the top of a shingle until it finds a way in.
The British Columbia Building Code is the legal baseline here. Section 9.26 says open valleys must be flashed with at least one layer of sheet metal not less than 600 mm wide, or two layers of roll roofing. So a narrow strip of metal is not just a poor detail. It falls short of the code.
A practical bonus: IKO notes that open valleys need less nailing in the valley itself, because the nails sit at the edges of the flashing, well away from the centre where the water runs.
Open vs closed valley at a glance
| Factor | Open metal valley | Closed-cut valley |
|---|---|---|
| Appearance | Visible metal strip, more architectural | Continuous shingle surface, traditional |
| Water and debris flow | Clear channel, debris washes through | Water runs over shingle layers, debris can catch |
| Moss and needles | Easier to see and clear | Harder to spot until staining or leaks appear |
| Where nails sit | Edges of the flashing | At least 150 mm from the centreline |
| Low-slope sections | Generally the safer choice | Code restricts closed valleys with rigid shingles on low slopes |
| Main installer risk | Untrimmed corners, exposed nails, narrow metal | Nails too close to centre, missing cement, poor overlap |
| Typical North Shore fit | Treed lots, additions, lower pitches | Open sightlines, steeper roofs, visible front slopes |
No table replaces looking at your roof, but it shows why the decision is rarely one-sided.
Which one suits your North Vancouver roof
Three questions settle most cases.
How steep is the valley?
Pitch matters. The BC Building Code states that closed valleys must not be used with rigid shingles below a set minimum slope(1 in 1.2 in the code text). IKO also says open valleys are strongly recommended on lower-pitched roofs because they shed debris faster. Many North Shore homes have an addition, porch or dormer roof that is flatter than the main roof. That is where we look first, because valley water moves more slowly and debris lingers.
What is growing over the roof?
If you have cedars, firs or maples overhead, we recommend an open valley. NRCA specifically recommends open valleys where foliage debris is a concern and in areas with frequent freeze-thaw cycling. A metal channel lets leaves and needles slide through, and you can see a build-up from the ground or during a seasonal inspection.
How cold does that slope get?
North Vancouver is mild by Canadian standards, but higher elevations, shaded slopes and cold snaps do bring snow and refreezing. NRCA lists enhancements for freeze-thaw areas, including stripping metal flanges with 9 to 12 inch strips of self-adhering polymer-modified bitumen underlayment, adding a closure at the eave and tapering the shingle cut. IKO adds that ice and water protection in valleys is typically at least 2 feet wide, and local code may require more. We cover that layer in more detail on our ice and water shield page and our page on roof underlayment installation.
Our rule of thumb: treed lot, lower pitch, or a roof that has leaked before in the valley means open metal. A steep, open, sunny front slope where the owner wants an uninterrupted shingle look can work with a closed-cut valley, built to the full CRCA detail. For a deeper side-by-side, see our post on which valley style sheds Vancouver rain better.
Our perspective
Hey, it’s Harman here. When we open up a leaking valley on the North Shore, the valley type is rarely the villain. The villain is a shortcut: metal too narrow, nails driven through the flashing, corners left square, or a closed-cut valley with nails sitting right where the water runs.
That is why we put the detail work first. When we install an open valley, we use wide corrosion-resistant metal, nail only at the edges, overlap and cement the joins, and clip the shingle corners so water cannot track sideways. When a homeowner wants a closed-cut valley, we build it to the Canadian trade guidance, with the nailing kept well back from the centreline and cement under the end shingles.
Our approach is designed around the roof in front of us, not a one-size-fits-all rule. A cedar-lined street in Lynn Valley is a different job from a clear south-facing slope in Edgemont. We would rather walk the roof, look at the valleys and the trees and then recommend one, than quote the same thing for every house.
Harman
Installation mistakes that cause valley leaks
If you are comparing quotes or reviewing a past job, these are the details to look for. They all come straight from the CRCA guidance above.
- Narrow flashing. Open valley metal under 600 mm (24 in) wide is below the code minimum.
- Exposed nails in the metal. The CRCA requires no exposed nails along the valley flashing. Nail heads in the channel are future leak points.
- Square, untrimmed corners. Without the 25 mm (1 in) clip, water can travel along the top of a shingle and find a path under it.
- Short filler shingles. Finishing a course into an open valley with a piece under 300 mm (12 in) is a shortcut that does not hold.
- No cement bed. End shingles should be embedded in a 75 mm (3 in) strip of plastic cement on both valley types.
- Nails too close to the centre in a closed-cut valley. The minimum is 150 mm (6 in) from the centreline.
- Missing or narrow underlayment. Valley underlayment goes on first. Without it, one failed nail becomes a ceiling stain.
One repair note matters for owners and stratas. We have written about why flashing patches in a valley often buy only weeks and about repeat valley leaks in a West Vancouver strata. The pattern is the same: a patch over a poorly built valley does not fix the valley. Our article on open valley leak repairs in North Vancouver also explains when a repair can trigger a permit, which is worth knowing before work starts.
Keeping valleys clear between roof jobs
A good valley still needs a look once or twice a year. For North Vancouver, we suggest checking after leaf drop in late fall and again after the wet season.
- Look for debris, moss and standing water in the valley from the ground or a safe vantage point, and use binoculars if you have them.
- Watch for staining on the ceiling below, or on the wall where a valley meets a dormer or sidewall.
- Check that shingle edges alongside an open valley are not lifting or curling.
- Leave the climbing and the clearing to a roofer. Wet moss and metal are slippery.
If you see damp patches under a valley after a heavy rain, call for an inspection before the next storm. Water running under a valley can soak the sheathing for a long time before it shows inside the house.
Strata councils and property managers with several buildings should add valleys to the yearly maintenance walk. Moss and debris build up predictably, so a scheduled clean is cheaper than an emergency call.
Talk to us about your valleys
We inspect, repair and replace asphalt shingle roofs for homeowners, strata corporations and commercial owners across the North Shore and Metro Vancouver. If you suspect a valley is failing, or you are planning a reroof and want to choose between open and closed, we can look at the roof and give you a straight recommendation. Start with our residential roofing services, or if you manage a building, see our strata and multifamily roofing services.
For active leaks, use our emergency roof repair service through the Paragon Roofing BC home page.
FAQ
Are open valleys better than closed valleys?
Not in every case, but for treed lots and lower pitches they usually perform better, because the metal channel keeps debris and water moving. Closed-cut valleys can perform well on steeper roofs when the nailing and cement details are followed. The installation quality matters more than the label.
Do closed valley shingles leak more often?
They can, when built poorly. The CRCA’s closed-cut method relies on nails kept at least 150 mm (6 in) from the centreline, clipped corners and cement under the end shingles. Skip those and water finds a way in. Built to that standard, a closed-cut valley is a sound detail on the right slope.
How wide should open valley metal be in BC?
The BC Building Code calls for at least one layer of sheet metal not less than 600 mm wide, or two layers of roll roofing. The CRCA manual also recommends corrosion-resistant metal at least 600 mm (24 in) wide. Ask your roofer to confirm the width and the metal in writing.
Can you convert a closed valley to an open valley?
Yes, but it means lifting the shingles along the valley, installing proper underlayment and wide metal flashing, then re-laying and trimming the shingles. It is usually best done during a reroof or a larger repair. We can assess whether it makes sense on your roof during an inspection.
Sources
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