Officially, Intel's Broadwell processor could only address RAM modules up to 8 GB thus far. This was also because of the fact that bigger SODIMMs were not available at the time. The small RAM manufacturer Intelligent Memory is the first to launch 16 GB modules which are compatible with current notebooks.
http://www.notebookcheck.net/Intelligent-Memory-16-GB-RAM-modules-for-Broadwell-notebooks.137492.0.html