Questions and Answers

Common engineering questions answered by our professional engineers.

A: The most likely backfill with no floor slab is concrete – full depth. Concrete backfill prevents flexure below the soil surface, allows for better lateral support and prevents uplifting of the post.

A: The most likely backfill with a concrete floor slab is either granular or sand. The international Building Code actually requires either concrete backfill or sand backfill, however, it has been found through experience that compacted, crushed 3/4 (-) rock is an excellent backfill. The presence of a floor slab also provides lateral support for the post.

A: Purlins can be installed stacked and lapped, stacked and butted or face hung. A stacked purlin stacks on top of the truss top chord. It is nailed to a purlin block that is nailed on each side to the top chord of both trusses. When the purlins are stacked and lapped one purlin laps over the other, usually about a foot in length. When the purlins are stacked and butted the two purlin boards butt together right in the middle of the purlin block. Purlins can also be installed flush with the top of the top chord of the trusses using joist hangers.

A: Commercial girts are typically required to resist high wind loads.

A: A commercial girt can be installed with blocks nailed to the post or with rotated joist hangers. The commercial girt (which is rotated 90 degrees to a flat girt) is nailed on top of a block and then toe nailed into the post. A commercial girt can also be installed with a joist hanger rotated 90 degrees and nailed directly to the post.