Purpose of this diagonal board on underside of deck?

Question

This board is nailed to the underside of the joists, and does not extend across the full width of the deck.
I'm planning to add a commercial under-deck ceiling, and would need to remove that board.
Would there be an issue removing that board?  What does it do?

Lee Sam · Accepted Answer

It’s a temporary brace...probably used temporarily during construction and they forgot to remove it. (Look close and you’ll see the end of the board is not fastened.)
The height of the deck above the ground has nothing to do with the use (or need) for a brace.

Ed Beal · Answer

With the deck that high the diagonal board stops the deck from wobbling. I might add a steel cable x to do the same thing in a much smaller profile. It could be drilled in but I would want both directions with cable.

Answered by Ed Beal on August 4, 2021

blacksmith37 · Answer

Diagonals are needed in square /rectangle construction to prevent distortion ( called "racking") and movement/wobble ; with no diagonals it will distort as a trapezoid . I would put in 2 X 6 diagonals between many of the joists. It could also be done with cables or steel straps but these are tension members only. A ceiling of something like 1/2 plywood wood also stiffen it. Generally the exterior wall corners of homes will have plywood sheathing to prevent this possible distortion. The diagonal board was to provide stability during construction ; houses under construction will many many of these temporary diagonals. Apparently they forgot to remove it and put in permanent diagonals.

Answered by blacksmith37 on August 4, 2021

Purpose of this diagonal board on underside of deck?

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