Floor joists

Just a few days after framing started, the first joists went up over the basement. Joists are horizontal structures that support and distribute weight from above (in this case, from the next floor).

Floor joists

Traditionally, floors were supported by either a) solid lumber joists or b) trusses, which are built out of solid lumber arranged in a series of connected triangles (think railroad bridge).

My house uses a newer product known as engineered wood joists, also called “I-joists.” I-joists are made up of two solid “flanges” with a thin “web” of engineered wood glued between them. Compared with traditional solid lumber, I-joists are stronger per their weight and less likely to deform over time. Compared with trusses, I-joists are easier to work with on a jobsite and less expensive. Downsides are that penetrations for electrical, plumbing or mechanical have to be cut carefully through the web to prevent a loss of strength, and the thin web between the flanges is more susceptible to fire than either trusses or solid lumber.

The strength of a structure built out of I-joists depends both on the both the size and materials of the individual I-joists and the spacing between joists. Joist spacing is dictated both by structural requirements and by code. Most residential projects use joists spaced between 12 and 24 inches on center apart.

Floor joists Floor joists

Photos taken December 18, 2019. Posted January 5, 2020.

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