When Richmond, Calif., builder Pete Kasten accepted a last-minute commission to renovate a third-floor bedroom and bath in a historic 8,000-square-foot home north of the Golden Gate Bridge, he knew that the impending late-winter rains had the potential to wreak all sorts of expensive havoc on the site. The job - part of a regional event to showcase the work of residential designers - called for tearing off an existing 15-by-36-foot roof, beefing up the framing, and installing a new membrane roof and floating ipe deck. The new deck was to be flush with the bedroom floor and separated from...

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