Shingle stagger…edge-to-edge spacing… single spacing…shingle offset…
Call it whatever you want, you should be looking at roof shingle stagger. Stagger is important because, if the spacing is less than 4 inches, water can travel from joint to joint under the shingles and create a leak in the roof.
Typical three-tab shingles of years past
Take a look at details of a typical three-tab shingle installation (Illustration). The edge-to-edge spacing (stagger) measures 6 inches. It’s easy to see whether there’s a problem with stagger: The tabs and cutouts don’t line up. Shingle stagger was rarely an issue when three-tab shingles were the norm.
When it’s hard to see stagger
We can see that the stagger is about 1.5 inches in this installation (Photo 1). The butt joints of the shingles were never tightly installed and the joints are worn. This is a defect.
In another case, it’s a little more difficult to identify the stagger (Photo 2). Because the shingle edges are not perfectly aligned, the spacing is more visible. The placement of my ruler also helps.
The California valley installation
In a “California valley,” a vertical shingle lines the edge of the valley (Photo 3). Note that the vertical shingle is run parallel to the metal flashing and then covered with horizontal shingles. It is tough to see, but my ruler shows spacing at about 4 inches—the minimum allowed.
The California valley installation is used to speed installation. The edges of the shingles are not cut; full shingles are just laid into the valley. This type of placement creates a problem on lower-slope roofs where the spacing becomes less than 4 inches. You may also see this California type of valley in a closed-cut installation without the metal flashing.
The takeaway
Architectural or laminated shingles can complicate your roof inspections because the shingle stagger is difficult to see. While improper spacing can result in appearance issues, we’re really concerned with improper spacing that can cause leaks.
Never ignore the shingle stagger. All industry standards, as well as shingle manufacturers’ instructions, mandate that the stagger should be greater than 4 inches. You won’t normally identify the type of shingle and installation instructions, but always make sure that the stagger is more than 4 inches.
To learn more, attend Tom’s technical presentations at educational sessions for ASHI chapters. Tom can also provide his knowledge for your educational event; contact him at Tom@HTOYH.com.