DILLINGHAM, Alaska—Tom Marsik and Kristin Donaldson are building a house a few minutes’ drive from the center of this small city, a two-story model with peat-brown vinyl siding that blends easily with the yellows and golds of the tundra in early autumn. The location is stunning, but it’s only from the inside that you see the building’s defining characteristic: White-painted walls that are more than two feet thick.