In designing a paint barn the designer must compromise finish quality in order to achieve the benefits of safety and health, while retaining a low-cost system. The designer looks at the design of a proper paint booth and regards as too costly the changes necessary to accomplish a perfect paint booth design. Several considerations are important to the designer in this rationale. One is access to the aircraft, previously done by tele-platforms. Multiple use of a paint facility (such as maintenance) leads to the use of bridge cranes that make it difficult to incorporate them into an insert. Use of fall protection around the top surfaces of a paint booth means rugged support structures.
The need for fall protection and elaborate access structure in a paint barn means that there are flat spots on the tops of beams and other items that overspray, dust, and even pollen in the springtime can settle onto. Once these particles are disturbed, they fall onto the object being painted causing a blemish and reducing quality. Steel beams are a particularly sought-after roost for birds and pigeons. While the inner walls of a paint barn can be sheathed with smooth drywall or sheet metal, the overhead steel and hanging items are another challenge altogether.
Lighting in a paint barn has been uniformly poor in past designs. In part, because the lights are typically further away from the aircraft than they would be in an insert, and there is very little, if any, lighting on the side walls. Typically the lights are high wattage HID lamps that drop from the ceiling. In cases where explosion proof lighting is required, the light fixtures become extremely expensive.
Airflow is calculated over the entire cross sectional area of the Barn even though the process does not use the air at the ceiling level. To reduce the airflow to a more reasonable level risks the degradation of laminar flow in the center of the plane (the wings) where a lot of paint is applied. As the air slows down and liquids are added to the air, the density of the air changes and the laminar flow degrades into eddies. This is visible as a cloud of overspray over the head of the painter.
This leaves only the problems with paint barns, such as poor painting quality and high instances of re-work. Good controlled airflow and high levels of lighting solve both of these problems. The very style of the paint barn rules these features out.