Although many .NET based programs still require version 3.5 of the Framework, this version won't be installed/enabled by default on Windows 8 / 8.1 / Server 2012 (R2) systems.
You can manually enable the .NET 3.5 feature using the control panel (and an Internet connection) or you can use Dism.exe and the \sources\sxs\ folder of your Windows installation medium (see Installing the .NET Framework 3.5 on Windows 8 or 8.1 and .NET Framework 4.5 is default and .NET Framework 3.5 is optional).
By v. 9.6, "WSUS Offline Update" will support the second (offline) way to have the .NET 3.5 Feature enabled under Windows 8 / 8.1 / Server 2012 (R2).
You may use "IntegrateSourcesSxsFolder.cmd" to integrate the required binaries into your WOU tree.
Be sure to specify the correct platform, architecture and language, otherwise subsequent installation/enabling attempts will fail, of course.