Most metal buildings (also known as steel buildings) are used for relatively utilitarian purposes — for example, as warehouses, auto repair shops, or manufacturing facilities. That said, it’s possible for a metal building to have a completely finished interior, in which case the building can be used as a retail store or even a high-end home.
Metal buildings have a post-and-beam steel frame (steel columns and rafters) overlaid on the exterior of the walls by horizontal steel girts. Steel purlins are installed above the rafters. To complete the system, the walls and roof are covered by steel panels.
Metal buildings have certain advantages: they allow for wide spans without intervening columns or supporting walls, and they’re relatively inexpensive. They also have a few disadvantages: the buildings’ fat columns can be hard to hide or disguise, and most metal buildings have an unsophisticated approach to insulation and air sealing.
Compared to wood-frame buildings, steel buildings are notable for their lack of wall sheathing or roof sheathing. For builders concerned with air sealing details or advanced insulation methods, the lack of sheathing raises a few concerns.
Most metal buildings are insulated with a product called MBI. You’re probably wondering, “What’s MBI?” That’s simple: MBI stands for Metal Building Insulation. Basically, it’s fiberglass insulation adhered to a white vinyl vapor barrier.
Installers drape the insulation over the roof purlins, and then install the steel roofing panels with screws through the insulation to the purlins. The wall insulation is usually hung on the exterior side of the steel girts, and the steel wall panels are screwed through the insulation into the girts.
[Image credit: CertainTeed — https://www.certainteed.com/resources/mb316.pdf]This method is fast and easy, but it introduces a major thermal weakness in the building exterior: at…