Passive House projects have slightly different materials used in the construction, therefore costs are not always the same as conventional housing projects. In the Greenport Passive House, the air barrier is achieved using Zip Sheathing and Zip tape. Exterior insulation of polyisocyanurate (4″ walls, 6″ roof) and 1″ wood furring is attached to the Zip Sheathing using long structural screws. This is unique to Passive House projects because the insulation used tends to be thicker than on a conventional house. In the end, over 5,000 screws were used to attach furring and insulation to the outside of the vapor barrier sheathing. The screws alone cost over $6,000.