With arctic conditions penetrating the mountain and causing the bedrock to remain at a temperature of 23°F, the envelope extends under the floor slab of the crawl space, which is fitted with R-40 insulation. The differential of interior and exterior temperatures and the high relative humidity required envelope detailing to focus on the reduction of thermal bridges and maintaining insulation continuity.

Photo by The Unfound door

Protecting the crawl space was key, as it holds storage tanks for the domestic water supply, which is trucked in when conditions permit. The crawl space also stores sanitary wastewater, which is hauled down the mountain to a municipal treatment plant.

During the first winter season, the team determined that working through winter was achievable if the summit highway remained open. Snowplows were deployed full-time to clear roads, escort employees and clear the jobsite. Going the extra mile to prepare for winter construction was paramount, as average winter temperatures at the summit stayed below -20°F. Measures were taken to prevent heavy equipment from freezing during excavation and rock removal. Periodic 160-mph wind gusts blew out the glass on vehicles and equipment.

Lightning storms would move onto the summit with little warning and shut down precast erection for up to an hour every day.