http://sridharkatakam.com/displaying-fixed-navigation-menu-upon-scrolling-genesis/

gistfile1.php

add_action( 'wp_enqueue_scripts', 'custom_enqueue_script' );
function custom_enqueue_script() {
	wp_enqueue_script( 'sticky-nav', get_stylesheet_directory_uri() . '/js/sticky-nav.js', array( 'jquery' ), '', true );
}

gistfile2.css

.nav-secondary {
    background-color: #333;
    border-bottom: 1px solid #111;
    border-top: 1px solid #111;
    clear: both;
    display: none;
    position: fixed;
    top: 0;
    width: 100%;
    z-index: 999;
}

.admin-bar .nav-secondary {
    top: 28px;
}

.nav-secondary .genesis-nav-menu a:hover {
	color: #fff;
}

.nav-secondary .genesis-nav-menu li li a:hover {
	color: #000;
}

.menu-secondary > li:first-child a {
    background: url("images/fixed-menu-logo.gif") no-repeat center center;
    margin-right: 10px;
    margin-right: 1rem;
    text-indent: -9999px;
    width: 180px;
}

sticky-nav.js

jQuery(function( $ ) {
	var starting_position = $('.site-header').outerHeight( true ) + $('.nav-primary').outerHeight( true );

	$(window).scroll(function() {
		var yPos = ( $(window).scrollTop() );
		if( yPos > starting_position && window.innerWidth > 500 ) { // show sticky menu after these many (starting_position) pixels have been scrolled down from the top and only when viewport width is greater than 500px.
			$(".nav-secondary").fadeIn();
		} else {
			$(".nav-secondary").fadeOut();
		}
	});
});