Adding a responsive mobile menu in any iThemes Builder theme. http://sridharkatakam.com/add-responsive-mobile-menu-builder-theme/

functions.php

// Enqueuing and Using Custom Javascript/jQuery
function custom_load_custom_scripts() {
if ( file_exists( get_stylesheet_directory() . '/js/custom_jquery_additions.js' ) )
    $url = get_stylesheet_directory_uri() . '/js/custom_jquery_additions.js';
else if ( file_exists( get_template_directory() . '/js/custom_jquery_additions.js' ) )
    $url = get_template_directory_uri() . '/js/custom_jquery_additions.js';
if ( ! empty( $url ) )
    wp_enqueue_script( 'custom_jquery_additions', $url, array('jquery'), false, true );
}
add_action( 'wp_enqueue_scripts', 'custom_load_custom_scripts' );

gistfile1.css

@import url(http://fonts.googleapis.com/css?family=Source+Sans+Pro:200,300,400,600,700,900,200italic,300italic,400italic,600italic,700italic,900italic|Merriweather:400,700,400italic,700italic,900,900italic,300italic,300);

gistfile2.css

/*********************************************
	Mobile Navigation Menu
*********************************************/

.it-mobile-menu {
	display: none;
}

gistfile3.css

.builder-module-navigation-background-wrapper {
	padding-top: 0.75em;
}

.builder-module-navigation.mobile .current_page_item a,
.builder-module-navigation.mobile .current-cat a,
.builder-module-navigation.mobile .current-menu-item a {
	background: #fbef05;
}

.builder-module-navigation.mobile li a:hover,
.builder-module-navigation.mobile .current_page_item li a:hover,
.builder-module-navigation.mobile .current-cat li a li a:hover,
.builder-module-navigation.mobile .current-menu-item li a:hover {
	background: #ECECEC;
	color: #5B7E39;
}

.builder-module-navigation li li {
	background: transparent;
}

style-mobile.css

/*********************************************
	Navigation Module (Mobile/Responsive)
*********************************************/

.builder-module-navigation.mobile {

}
.builder-module-navigation.mobile .builder-module-navigation-menu-wrapper {
    display: inherit;
    margin: 0;
}
.builder-module-navigation.mobile ul {
	margin-top: .5em;
	background: #FFFFFF;
}
.builder-module-navigation.mobile li {
	width: 100%;
	position: relative;
}

/* second level stuff */

.builder-module-navigation.mobile li ul {
	position: relative !important;
	left: 0 !important;
	border: 0;
	width: 100%;
	margin: 0;	
}
.builder-module-navigation.mobile li a,
.builder-module-navigation.mobile .current_page_item li a,
.builder-module-navigation.mobile .current-cat li a,
.builder-module-navigation.mobile .current-menu-item li a {
	margin: 0;
	background: transparent;
	border-color: transparent;
	color: #3B3F42;
	border-bottom: 1px solid rgba(0,0,0,0.1);
}
.builder-module-navigation.mobile li a:hover,
.builder-module-navigation.mobile .current_page_item li a:hover,
.builder-module-navigation.mobile .current-cat li a li a:hover,
.builder-module-navigation.mobile .current-menu-item li a:hover {
	background: #423737;
	color: #ECECEC;
}
.builder-module-navigation.mobile li li {
	border: 0;
	width: 100%;
}
.builder-module-navigation.mobile li ul ul {
	margin: 0;
}
.builder-module-navigation.mobile li li a {
	padding: .25em 0 .25em 2em;
	line-height: inherit;
}
.builder-module-navigation.mobile li li li a {
	padding-left: 4em;
}
.builder-module-navigation .menu.it-mobile-menu-hidden {
	display: none;
}
.it-mobile-menu {
	font-family: 'Source Sans Pro', 'Playfair Display', 'Helvetica Neue', Helvetica, Arial, sans-serif;
	text-transform: uppercase;
	color: #3B3F42;
	padding: .25em .75em;	
	display: block;
	cursor: pointer;
	-webkit-font-smoothing: antialiased;	
}