Chalk Line

A chalk line is one of the simplest and oldest layout tools in construction. It consists of a string wound on a reel inside a case filled with powdered chalk. When the string is pulled out it picks up a coating of chalk; stretched taut between two points and plucked, it snaps against the surface and leaves a straight line. Chalk lines are mentioned in Homer's Iliad and were used in ancient Egypt, and East Asian carpenters use a related ink line, known in Japan as the sumitsubo.

Uses in roofing

• Shingle courses: snapping horizontal lines across the deck keeps courses straight and exposure consistent, compensating for uneven eaves or decks.
• Vertical offset lines: lines up the slope set the stagger (offset) pattern for shingle joints.
• Starter courses and eave lines, especially where the eave is not straight.
• Battens and counter-battens for tile and slate roofs, marked at the correct gauge (spacing) for the tile or slate headlap.
• Metal panel layout: square reference lines for the first panel and for panel spacing.
• Low-slope membranes: alignment lines for rolls, fastener rows and insulation boards.
• Cut lines on panels, boards and membranes.

Chalk colours

Chalk is sold in several colours. Blue and white chalks are generally used where marks should weather away, while red and other strong colours are often marketed as more permanent and can stain roofing materials and paint. Manufacturers also sell weather-resistant and fluorescent formulations. Choosing a colour that will not permanently mark visible surfaces matters on finished roofs, metal panels and light-coloured membranes.

Technique

Measure and mark both ends of the line, hook or hold one end, pull the line taut, lift it straight up from the surface in the middle and release it. On long runs or windy days, a helper holds the centre and snaps each half. Lines snapped on wet surfaces may smear, and lines on very steep roofs may need to be refreshed as work progresses. A tape measure, square and pencil complete the basic layout kit.