How to Snap Chalk Lines for Straight Shingle Courses
Straight courses come from lines, not from eyeballing the eave. Horizontal exposure lines and vertical bond lines keep the whole roof true.
- Intermediate
- 30 minutes to 1 hour per slope
- Updated
The short answer
Snap a horizontal line for the first course, then more horizontal lines up the roof every 4 to 6 courses, spaced at the shingle exposure (about 5-5/8 inches for laminated shingles). Add vertical bond lines to keep the offset pattern straight. Do not follow a crooked eave; measure from the ridge and adjust the exposure slightly across many courses to land courses on the ridge.
A shingle roof that looks crooked is nearly always crooked because the courses drifted, one nail at a time, away from a true line. The shingles are straight. The starting line, or the lack of one, is not. A few minutes with a chalk line, before the first course and then every few courses, is what separates a roof that looks straight from every angle and one that wanders.
There are two kinds of lines. Horizontal lines run across the roof parallel to the eave and keep the exposure consistent from bottom to top. vertical bond lines run up the roof and keep the offset pattern of shingle ends where it should be. Both are snapped on the underlayment, and both are temporary.
Lines come after the eave edge and starter strip are in and before laying shingle courses. They use the exposure printed on the wrapper for the shingle.
Tools
- Chalk line reel, 100 foot
- Tape measure
- Framing square
- Shingle gauge or hatchet with exposure gauge
- Pencil or lumber crayon
- Helper for long runs
Materials
- Blue chalk, used for temporary lines
- Red chalk only when a permanent line is wanted, because it stains
- Underlayment in place on a dry deck
Safety first
- Do not back up to snap a line near the eave or rake. Kneel and stay tied off, because a line snapped with a step back is how roofers walk off edges.
- Keep a hand on the line and the reel. A dropped chalk reel slides down the roof.
- Do not snap lines on a wet or frosty deck. The chalk will not mark, and the surface is a slip risk.
Step by Step
Step 1: Check the exposure and the roof geometry
Most laminated shingles have an exposure of about 5-5/8 inches. Most 3-tab shingles have 5 inches. Confirm on the wrapper. Measure the slope from the bottom of the starter to the ridge in a few places, since the eave and the ridge are often not parallel.
Divide the run by the exposure to see where the last course lands. A remainder of a fraction of an inch can be spread across many courses by adjusting each exposure a hair. That is better than ending with a thin strip at the ridge.
Step 2: Snap the first course line
The first course sits on top of the starter and overhangs the eave by the same amount. Measure from the lower edge of the starter up by one exposure, mark at each end and at a third point, and snap the line. Check that the marks are consistent.
If the eave is not straight, follow the line, not the eave. A slightly bent eave hidden by a straight first course is invisible. A straight eave with a crooked course line is not.
Step 3: Snap horizontal exposure lines up the roof
For laminated shingles at 5-5/8 inches, 4 courses is 22-1/2 inches and 6 courses is 33-3/4 inches. Mark at both ends and at least one point in the middle, then snap. On a long run, pull the line tight and have a helper hold the far end.
Between lines, use a shingle gauge on the hammer or a mark on the nailer base to keep each course at the exposure. The lines catch drift before it grows.
Tip: Snap lines on the underlayment where you can see them, and use blue chalk. Red chalk stains and can show through light shingles.
Step 4: Check the lines against the ridge
A course that finishes with a thin sliver at the ridge looks poor and is hard to nail. If the remainder is off by a half inch or less, adjust the last several lines by a hair each, within the tolerance the manufacturer allows. Shingles with slightly stretched exposure are fine. Large changes are not.
Check at both ends of the slope. On a roof where the ridge is not level, the lines may need to diverge slightly, so that courses adapt to it.
Step 5: Snap vertical bond lines
Vertical lines are used to keep the shingle ends in the pattern. For a racking pattern, where shingles are laid straight up the roof in a stair-step, a line shows the edge of each shingle in the stack. For a 6 inch offset pattern, lines are used to keep the diagonal of joints consistent.
Start at a true line. Square off from the eave with a framing square, or use the 3-4-5 method on a large roof. Do not start from the rake unless the rake is plumb. A rake that is out of square pushes every course off.
Step 6: Deal with a crooked eave or a wandering rake
Old houses are rarely square. The eave may sag or the rake may lean. Rather than following the eave up the roof, pick a straight line and bring the courses to it. Over 3 to 4 courses, a small taper is invisible.
Where the difference is large, see how to lay shingle courses and offsets for how to feather the variation across the first courses. A crooked eave on a roof with a hip also affects the hip lines: see how to shingle a hip roof.
Step 7: Re-snap lines after walking and weather
Snap lines for the next section while the current one is being nailed. Lines on a dry deck last through a day of work. On a wet or dewy morning, wait until the deck is dry, or use a lumber crayon to mark the ends and snap when it can be seen.
Keep the chalk dry and the string clean. A chalk line that is damp will not leave a clear mark.
Exposure Reference
These are common values. The wrapper gives the correct exposure for the product.
- Laminated shingles: about 5-5/8 inches, so 4 courses is 22-1/2 inches.
- 3-tab shingles: 5 inches, so 4 courses is 20 inches.
- Hip and ridge cap: varies by product, commonly about 5 to 5-5/8 inches.
Long Runs and Big Roofs
On a long run, a chalk line sags in the middle and snaps with a curve. Pull it tight, hold it at both ends, and have a helper press the middle to the deck. For runs over about 40 feet, snap in two halves, checking that they meet. Wind makes it harder, so wait for a calm moment.
Common Mistakes
- Following the eave up the roof. A crooked eave makes every course crooked. Snap a true line.
- Snapping lines too far apart. Drift grows between lines. Snap every 4 to 6 courses.
- Starting vertical lines from an unsquared rake. Every course moves off, and the error grows toward the ridge.
- Ignoring the ridge. A course that finishes as a sliver at the ridge is hard to fasten and looks bad. Adjust exposure across many courses.
- Using red chalk. It stains the roof and can show through a light shingle.
- Snapping on wet underlayment. The line will not show and will have to be done again.
When to Call a Professional
Chalk lines are a homeowner-level skill, but roofs with hips, dormers and valleys need a plan for how the lines meet. If the roof is not square, has multiple pitches or is steep enough that kneeling is unsafe, have a roofer lay it out.
A roofer will often lay out a full roof of lines before a single shingle goes on. That is how a cut-up roof ends up with courses that line up where two planes meet.
Fraser Roofing does free roof inspections across the Fraser Valley, from Hope to Abbotsford. See our Roof Replacement service or the towns we cover.
How to Snap Chalk Lines for Shingle Courses: Questions
How far apart should chalk lines be for shingles?
Snap a horizontal line every 4 to 6 courses, which for laminated shingles at 5-5/8 inches of exposure is about 22-1/2 to 33-3/4 inches apart. Lines closer together keep drift smaller, and lines further apart save time but let errors grow. A line at each change of plane also helps.
What is the exposure for architectural shingles?
Most laminated or architectural shingles have an exposure of about 5-5/8 inches, which is 143 millimetres. Each product has its own figure, printed on the bundle wrapper, and the manufacturer's installation instructions govern. A slightly different exposure changes the number of courses and the coverage per bundle.
How do you keep shingle courses straight?
Snap a true first-course line, then horizontal lines every few courses, and check the courses against them as you go. Do not follow the eave if it is crooked. Use a hammer or nailer gauge set to the exposure between lines, and check the run to the ridge early so you can adjust.
Do you need vertical chalk lines for shingles?
They are not required, but they help keep the offset pattern straight, especially when racking or laying a stair-step pattern. A vertical line also helps where courses meet at a valley or hip. Many roofers use them on the first few courses and then work by eye.
What if the eave is not straight?
Snap the first-course line straight and let the starter follow the eave, then use the first few courses to absorb the difference. A small curve in the eave disappears over 3 or 4 courses. If the eave is badly out of line, the fascia and framing may need attention before roofing.
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This guide is general education. Always follow the product manufacturer's installation instructions, the BC Building Code and WorkSafeBC requirements, which take priority over anything written here.
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