I'm having some issues with Foundation 6 files, for some reasons they are just not including all of the sass components. I tried to use Foundation 5 and it worked fine. 
Here is my gulp task:
gulp.task('styles', ['clearCss'], function() {
    gulp.src('assets/sass/app.scss')
        .pipe(plumber(plumberErrorHandler))
        .pipe(sourcemaps.init())
        .pipe(sass({
            outputStyle: 'compressed'
        })
        .on('error', notify.onError(function(error) {
            return "Error: " + error.message;
        }))
        )
        .pipe(autoprefixer({
            browsers: ['last 2 versions', 'ie >= 9']
        }))
        .pipe(sourcemaps.write('.'))
        .pipe(gulp.dest('./assets/dist/css')) 
        .pipe(browserSync.stream({match: '**/*.css'}))
        .pipe(notify({
            message: "Styles task complete!"
        }));
});
And here is my app.scss:
// Import Foundation
@import "../components/foundation/scss/foundation";
It works with my own sass files, but completely ignoring foundation parts.