Fiber-Cement Siding

A couple of fiber-reinforced cementitious siding products have been getting a lot of attention in the sustainable building community recently. These products have some advantages, especially when they are used to replace top-quality wood products that come from old-growth forests. They also provide excellent fire ratings and good long-term durability (under the right conditions). Other environmental advantages are hard to find, however. On the whole, their report card as “green” building products is mixed at best.

Hardiplank™ from James Hardie Building Products is a new product in North America, but an old one in Australia. It is manufactured in a plant in central California from Portland cement, virgin wood fibers (imported from New Zealand), sand, and water. The ingredients are mixed into a slurry and deposited in layers on a roller. When the desired thickness is reached, the roller off-loads the wet sheets onto conveyers, where the sheets are cut to length and width using high-pressure water jets. The individual pieces are then cured in an autoclave, which uses high temperature and pressure to reduce the curing time for the cement from 28 days to 12 hours.