Classicthesis chapter title formatting

Question

How can I modify ClassicThesis to format chapter headings with the word "Chapter" followed by the roman numeral chapter number, a verticle space, and the chapter title? As many know, the default looks like:

While the desired (nay, required) would look like:

I have written the whole thing using lyx, and have been able to change many things to match required formatting.

Answer 1

You can add the following code to your preamble, just before \begin{document}:

\newcommand{\RNum}[1]{\uppercase\expandafter{\romannumeral #1\relax}}
\def\ifNumPutRoman#1{%
  \if!\ifnum9<1#1!\else_\fi
    \RNum{#1}\else#1\fi}

\titleformat{name=\chapter}[display]%             
        {\relax}
        {\centering{CHAPTER \ifNumPutRoman{\thechapter}} \\ }%
        {10pt}%
        {\centering\spacedallcaps}[\normalsize\vspace*{2\baselineskip}]%

Which gives you this:

\RNum converts thechapter to roman numerics, however, it first needs to be checked if it is a number or not. This could happen when \chapter{} is called in appendix part. The next command, \ifNumPutRoman takes care of this. Credit for this check goes to this answer.