The Sweat Equity column in the San Francisco Chronicle today steered readers to a UC PowerPoint presentation on the Web that provides details on fire-resistance ratings for roofs.

Produced by UC Cooperative Extension wood durability advisor Steven Quarles, the 18-slide presentation gives viewers an understanding of how roof coverings get their fire rating.

The information in Sweat Equity, a regular home improvement column written by brothers Bill and Kevin Burnett, was prompted by a reader question about whether an existing shake roof can be treated for...