Query posts by custom taxonomy ID

Question

I have a custom post type called portfolio and a custom taxonomy called build-type (acting as categories)

I am trying to query portfolio posts by build-type ID e.g. all Portfolio posts in "Hotels" (id=4 for that taxonomy)

// gets the ID from a custom field to show posts on a specific page   
$buildType = get_post_meta($post->ID, 'build_type_id', true);
// run query
query_posts(array( 
    'post_type' => 'portfolio',
    'showposts' => -1,
    'tax_query' => array(
        'taxonomy' => 'build-type',
        'terms' => $buildType,
        'field' => 'term_id'
    ),
    'orderby' => 'title',
    'order' => 'ASC'
));

Currently it's calling all portfolio posts and not just those with the build-type ID

For 'field' => 'term_id' should I be using term_id, tag_ID, id or something else?

Anyone know how to get this working?

Thanks in advance!