[joey44]

I would like to buy several BILLY bookshelves but would prefer not to use the back panel so as to leave my beautiful brick wall somewhat visible through the rows of books. Will this interfere with structural integrity of the bookcases? Is the back panel necessary? Are there alternate solutions?

[ted]

Yes, it prevents the unit from torquing.
The LACK shelving unit is backless.

[joey44]

Can we use the metal x-bars to stabilize instead of the back panel?

[jgsearls]

This couple didn't use the back of their Billy bookcase.

Office Progress: Bookcase Building | Young House Love

'Course they just did this project so we should check in in a year or so and see how it's holding up.

[JHSurf]

Originally Posted by joey44

Can we use the metal x-bars to stabilize instead of the back panel?

You should be able to use a metal cross brace. The included back piece is intended to keep the outer casing square. The metal cross-braces will accomplish the same thing.

Are you installing more than one Billy side-by-side? If so, you could connect all the cases and have a single set of cross-braces across the entire group of cases. This would probably leave more of the brick exposed through the book case.