Is there a better way to filter Genesis structural class names?

genesis_markup

<?php
/*
 * How do I append a class "row" to the class "site-header" as opposed to recreating "site-header" like I am here?
 *
 */

add_filter( 'genesis_attr_site-header', 'ssm_site_header' );
/*
 * Add the appropriate foundation class to site-header 
 *
 */
function ssm_site_header() {
	$attributes['class'] = 'site-header row';
	return $attributes;
}

Maybe:

$classes = $attributes['class'];
$attributes['class'] = $classes . ' row';
return $attributes;

or:

$classes = $attributes['class'];
$myclasses = " row";
$attributes['class'] = $classes . $myclasses;
return $attributes;

<?php
add_filter( 'genesis_attr_site-header', 'ssm_site_header' );
/*
 * Add the appropriate foundation class to site-header 
 */
function ssm_site_header( $atts ) {
    $classes = explode( ' ', $atts['class'] );
    $classes[] = 'row';
    $atts['class'] = implode( ' ', array_unique( $classes ) );
    return $atts;
}

Or an easier way so that you don't have to mess with any markup.

ex.

.wrap {
@extend .row;
}

.content {
@extend .large-9, .columns;
}