A quick hint about installing WAC Server. As it happens, Office Web Apps Server 2013 only added support for 2012R2 with SP1, and even though SP1 is about 3x the file size of RTM, you cannot install it without RTM; RTM setup fails and that’s where I found myself this morning.
Copy SP1 files to ‘updates’ folder
Download the service pack 1 for WAC Server from this link: http://go.microsoft.com/fwlink/p/?LinkId=510097
Then extract the service pack using /extract to a folder on the disk. Like this:
Now copy all the extracted files into the “updates” folder of the RTM install files. Once the updates are there, RTM setup works on 2012R2 and automatically installs SP1, too.
Note: Make sure to follow other requirements, as listed on TechNet