A building contractor was asked to cover a steel building with a traditional tile roof, but had a few questions about how to specify the roof. In particular, he needed to know the rafter sizing, spacing, and how to tie the rafters down, considering there is no traditional wall plate for the rafters to sit on. The contractor requested the solution ASAP, preferably the same day.
We inspected the calculation package for the steel frame provided by the structural engineer to find the relevant information to answer the questions. Namely, the building dimensions, the loading applied to the roof i.e., the allowed mass of the tiles, the allowed mass of the tile battens and roof membrane, the allowed mass of the rafters, the expected wind and snow loading.
We then computed a few variations of the rafter size and spacing that would be capable of carrying the roof load between the steel purlins. The lowest cost suitable option was then selected. We also calculated various options for tying the roof down, using various methods/materials. The one chosen was the simplest one using the most off the shelf parts.
This was completed and delivered within 6 hours.
A CAD drawing depicting the roof layout, detailing rafter size, space and method of tying the method to the steel purlins.