Is there a top or bottom to a TJI® joist?

Structurally, no, TJI® joists are manufactured without camber and with uniform properties regardless of orientation. However, the location of the pre-punched knockout holes will tend to be nearer one flange, so a builder might choose to install them with the holes down, to ease wiring or plumbing installations. Installing TJI® joists in a roof, with the holes near the top, might allow a builder to gain some cross ventilation from joist bay to joist bay.

One additional reason to pay attention to orientation of the joists is the use of TJI® Flak Jacket fire protection. In this case, the fire resistance of the product is dependent upon proper installation of the joist ("Up" direction is shown on the web of the joist).

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