Hardie Board Calculator

Fiber cement siding is Portland cement, ground sand, cellulose fiber, and water, formed under pressure and cured, which gives it dimensional stability, non-combustibility, and immunity to rot and insects at roughly 2.3 pounds per square foot in 5/16 inch lap thickness. Quantity is driven by exposure rather than by plank width: an 8-1/4 inch plank installed with the required minimum overlap of about 1-1/4 inches yields roughly 7 inches of exposure, so a 12 foot plank covers close to 7 square feet, while a 4 by 8 panel covers 32 and a shingle panel about 3.5. The takeoff is gross wall area minus window and door openings, plus a waste factor, divided by coverage per piece. Use 10 percent waste on plain rectangular walls and 12 to 15 percent where gables, numerous openings, or heavy trim force cutting, and add trim separately in linear feet for corners, casing, frieze, and fascia. Installed cost commonly lands between 8 and 14 dollars per square foot including labor and accessories. Three requirements shape the work. Fasteners must be corrosion resistant and penetrate framing by at least about 1-1/4 inches, blind nailed near the plank top and never overdriven, since an overdriven head crushes the board. A weather-resistive barrier with integrated flashing is mandatory behind the cladding. And cutting releases respirable crystalline silica, so shears, score-and-snap, or dust-collected blades with respiratory protection are required rather than optional.

Fiber cement began with the Austrian industrialist Ludwig Hatschek, who in 1900 patented a process for forming thin sheets from a slurry of cement and asbestos fiber on a modified paper machine, marketed under the name Eternit. The board was inexpensive, non-combustible, and rot-proof, and it spread worldwide as roofing and cladding through the first half of the twentieth century. James Hardie and Company, founded in Melbourne, Australia in 1888 as an importing business, became one of the major southern hemisphere manufacturers of asbestos cement building products. The modern product exists because the reinforcing fiber had to change. As the occupational disease burden of asbestos became undeniable, manufacturers sought substitutes, and the company removed asbestos from its building products during the 1980s, replacing it with refined cellulose fiber from wood pulp. Cellulose-reinforced fiber cement proved tougher and considerably easier to cut and nail than the asbestos formulations it displaced. The company entered the North American market around 1990 and built domestic manufacturing, and fiber cement grew from a niche import into one of the leading exterior claddings in the United States. Two forces drove that growth: wildfire and urban conflagration codes that favor non-combustible surfaces, and the development of climate-specific product formulations after freeze-thaw and humidity performance differences between regions were documented in field studies.