The National Park Service offers this website on the exterior skin of a house, which is defined as a "weather envelope" that "typically includes all the surfaces of its functional and decorative features --roof, chimney, exterior walls, woodwork, windows, porches, doors, and the above-ground portion of the foundation." The site provides some basic pointers on taking care of a historic house. Topics include: What the "Skin" Does, How Your House is Connected, What & When to Repair, and Beyond Maintenance.