Single-digit temperatures and frozen ground are wreaking havoc on construction schedules across northern Nevada.Sub-freezing temperatures and record lows froze activity at construction sites from Lake Tahoe to Elko, forcing contractors to scramble to meet deadlines and oftentimes delaying crucial first-quarter revenue.In Truckee, where temperatures routinely dip well below zero, Clark & Sullivan Construction of Sparks is building an 8,500-square-foot clubhouse at Shaffer's Mill golf course. Superintendent Steve Jessup is forced to heat the lock to the job trailer with a hand-held blowtorch to gain entry in the mornings.In Sparks, where Gradex is performing site work for a new Maverick gas …