A reusable solution for adding element classes in the Genesis framework.

gistfile1.php

<?php

/**
 * General function for adding element classes in Genesis
 */
function add_gen_classes( $attr, $classes, $layout = NULL ){
    
    // If there's a layout parameter, and current layout does not match, return classes unchanged
    // This part is pseudo code - not sure if this is the function for testing current layout
    if ( $layout && ! genesis_site_layout( $layout ) )
        return $attr;

    $classes = '';
    foreach( $classes as $class ){
        $classes .= ' ' . $class;
    }
    $attr['class'] .= $classes;
    return $attr;
}

/* Using the function */
add_filter( 'genesis_attr_site-header', function( $attr ){
    return add_gen_classes( $attr, array('row','other-class'), 'layout' );    
});