Because a standard sheet of drywall is Â½â thick, once installed, the width and depth of the closet will be reduced by 1â³ each. In other words, if the reach-in closet is framed at 24â³ deep, it will be 23â³ in depth after drywall.irst of all, as mentioned above, clothing hangs away from the back wall 24 inches. If a reach-in closet is 24 inches deep, any clothing hanging behind the return wall is completely hidden from view and difficult to access.