how to skip SASS compilation in Ember Broccoli build

I'm compiling an Ember.js app using broccoli and currently I'm working only on the JavaScript files. The SASS stylesheet files are not being changed at all, yet our Broccoli build is always building new CSS out of those stylesheets.

How do I turn this off?

How can I make Broccoli only build JavaScript files or only build SASS files? It's really slowing down my compile times when I change a JS file but a SASS file is compiled.