Hide header until it is needed in WordPress using Headroom.js. http://sridharkatakam.com/hide-header-needed-wordpress-using-headroom-js/

animations.min.css

.animated{-webkit-animation-duration:.5s;-moz-animation-duration:.5s;-o-animation-duration:.5s;animation-duration:.5s;-webkit-animation-fill-mode:both;-moz-animation-fill-mode:both;-o-animation-fill-mode:both;animation-fill-mode:both}@-webkit-keyframes slideDown{0%{-webkit-transform:translateY(-100%)}100%{-webkit-transform:translateY(0)}}@-moz-keyframes slideDown{0%{-moz-transform:translateY(-100%)}100%{-moz-transform:translateY(0)}}@-o-keyframes slideDown{0%{-o-transform:translateY(-100%)}100%{-o-transform:translateY(0)}}@keyframes slideDown{0%{transform:translateY(-100%)}100%{transform:translateY(0)}}.animated.slideDown{-webkit-animation-name:slideDown;-moz-animation-name:slideDown;-o-animation-name:slideDown;animation-name:slideDown}@-webkit-keyframes slideUp{0%{-webkit-transform:translateY(0)}100%{-webkit-transform:translateY(-100%)}}@-moz-keyframes slideUp{0%{-moz-transform:translateY(0)}100%{-moz-transform:translateY(-100%)}}@-o-keyframes slideUp{0%{-o-transform:translateY(0)}100%{-o-transform:translateY(-100%)}}@keyframes slideUp{0%{transform:translateY(0)}100%{transform:translateY(-100%)}}.animated.slideUp{-webkit-animation-name:slideUp;-moz-animation-name:slideUp;-o-animation-name:slideUp;animation-name:slideUp}@-webkit-keyframes swingInX{0%{-webkit-transform:perspective(400px) rotateX(-90deg)}100%{-webkit-transform:perspective(400px) rotateX(0deg)}}@-moz-keyframes swingInX{0%{-moz-transform:perspective(400px) rotateX(-90deg)}100%{-moz-transform:perspective(400px) rotateX(0deg)}}@-o-keyframes swingInX{0%{-o-transform:perspective(400px) rotateX(-90deg)}100%{-o-transform:perspective(400px) rotateX(0deg)}}@keyframes swingInX{0%{transform:perspective(400px) rotateX(-90deg)}100%{transform:perspective(400px) rotateX(0deg)}}.animated.swingInX{-webkit-transform-origin:top;-moz-transform-origin:top;-ie-transform-origin:top;-o-transform-origin:top;transform-origin:top;-webkit-backface-visibility:visible!important;-webkit-animation-name:swingInX;-moz-backface-visibility:visible!important;-moz-animation-name:swingInX;-o-backface-visibility:visible!important;-o-animation-name:swingInX;backface-visibility:visible!important;animation-name:swingInX}@-webkit-keyframes swingOutX{0%{-webkit-transform:perspective(400px) rotateX(0deg)}100%{-webkit-transform:perspective(400px) rotateX(-90deg)}}@-moz-keyframes swingOutX{0%{-moz-transform:perspective(400px) rotateX(0deg)}100%{-moz-transform:perspective(400px) rotateX(-90deg)}}@-o-keyframes swingOutX{0%{-o-transform:perspective(400px) rotateX(0deg)}100%{-o-transform:perspective(400px) rotateX(-90deg)}}@keyframes swingOutX{0%{transform:perspective(400px) rotateX(0deg)}100%{transform:perspective(400px) rotateX(-90deg)}}.animated.swingOutX{-webkit-transform-origin:top;-webkit-animation-name:swingOutX;-webkit-backface-visibility:visible!important;-moz-animation-name:swingOutX;-moz-backface-visibility:visible!important;-o-animation-name:swingOutX;-o-backface-visibility:visible!important;animation-name:swingOutX;backface-visibility:visible!important}@-webkit-keyframes flipInX{0%{-webkit-transform:perspective(400px) rotateX(90deg);opacity:0}100%{-webkit-transform:perspective(400px) rotateX(0deg);opacity:1}}@-moz-keyframes flipInX{0%{-moz-transform:perspective(400px) rotateX(90deg);opacity:0}100%{-moz-transform:perspective(400px) rotateX(0deg);opacity:1}}@-o-keyframes flipInX{0%{-o-transform:perspective(400px) rotateX(90deg);opacity:0}100%{-o-transform:perspective(400px) rotateX(0deg);opacity:1}}@keyframes flipInX{0%{transform:perspective(400px) rotateX(90deg);opacity:0}100%{transform:perspective(400px) rotateX(0deg);opacity:1}}.animated.flipInX{-webkit-backface-visibility:visible!important;-webkit-animation-name:flipInX;-moz-backface-visibility:visible!important;-moz-animation-name:flipInX;-o-backface-visibility:visible!important;-o-animation-name:flipInX;backface-visibility:visible!important;animation-name:flipInX}@-webkit-keyframes flipOutX{0%{-webkit-transform:perspective(400px) rotateX(0deg);opacity:1}100%{-webkit-transform:perspective(400px) rotateX(90deg);opacity:0}}@-moz-keyframes flipOutX{0%{-moz-transform:perspective(400px) rotateX(0deg);opacity:1}100%{-moz-transform:perspective(400px) rotateX(90deg);opacity:0}}@-o-keyframes flipOutX{0%{-o-transform:perspective(400px) rotateX(0deg);opacity:1}100%{-o-transform:perspective(400px) rotateX(90deg);opacity:0}}@keyframes flipOutX{0%{transform:perspective(400px) rotateX(0deg);opacity:1}100%{transform:perspective(400px) rotateX(90deg);opacity:0}}.animated.flipOutX{-webkit-animation-name:flipOutX;-webkit-backface-visibility:visible!important;-moz-animation-name:flipOutX;-moz-backface-visibility:visible!important;-o-animation-name:flipOutX;-o-backface-visibility:visible!important;animation-name:flipOutX;backface-visibility:visible!important}@-webkit-keyframes bounceInDown{0%{opacity:0;-webkit-transform:translateY(-200px)}60%{opacity:1;-webkit-transform:translateY(30px)}80%{-webkit-transform:translateY(-10px)}100%{-webkit-transform:translateY(0)}}@-moz-keyframes bounceInDown{0%{opacity:0;-moz-transform:translateY(-200px)}60%{opacity:1;-moz-transform:translateY(30px)}80%{-moz-transform:translateY(-10px)}100%{-moz-transform:translateY(0)}}@-o-keyframes bounceInDown{0%{opacity:0;-o-transform:translateY(-200px)}60%{opacity:1;-o-transform:translateY(30px)}80%{-o-transform:translateY(-10px)}100%{-o-transform:translateY(0)}}@keyframes bounceInDown{0%{opacity:0;transform:translateY(-200px)}60%{opacity:1;transform:translateY(30px)}80%{transform:translateY(-10px)}100%{transform:translateY(0)}}.animated.bounceInDown{-webkit-animation-name:bounceInDown;-moz-animation-name:bounceInDown;-o-animation-name:bounceInDown;animation-name:bounceInDown}@-webkit-keyframes bounceOutUp{0%{-webkit-transform:translateY(0)}30%{opacity:1;-webkit-transform:translateY(20px)}100%{opacity:0;-webkit-transform:translateY(-200px)}}@-moz-keyframes bounceOutUp{0%{-moz-transform:translateY(0)}30%{opacity:1;-moz-transform:translateY(20px)}100%{opacity:0;-moz-transform:translateY(-200px)}}@-o-keyframes bounceOutUp{0%{-o-transform:translateY(0)}30%{opacity:1;-o-transform:translateY(20px)}100%{opacity:0;-o-transform:translateY(-200px)}}@keyframes bounceOutUp{0%{transform:translateY(0)}30%{opacity:1;transform:translateY(20px)}100%{opacity:0;transform:translateY(-200px)}}.animated.bounceOutUp{-webkit-animation-name:bounceOutUp;-moz-animation-name:bounceOutUp;-o-animation-name:bounceOutUp;animation-name:bounceOutUp}

functions.php

//* Enqueue Headroom
add_action( 'wp_enqueue_scripts', 'sk_enqueue_scripts' );
function sk_enqueue_scripts() {

	if ( wp_is_mobile() )
		return;

	wp_enqueue_style( 'animations',  get_stylesheet_directory_uri() . '/css/animations.min.css' );

	wp_enqueue_script( 'headroom', get_stylesheet_directory_uri() . '/js/headroom.min.js', '', '', true );
	wp_enqueue_script( 'jquery-headroom',  get_stylesheet_directory_uri() . '/js/jQuery.headroom.min.js', array( 'jquery' ), '1.0.0', true );
	wp_enqueue_script( 'headroom-init',  get_stylesheet_directory_uri() . '/js/headroom-init.js', array( 'jquery-headroom' ), '1.0.0', true );

}

headroom-init.js

jQuery(document).ready(function($) {

	$(".site-header").headroom({
		// scroll tolerance in px before state changes
		"tolerance": 0,

		// vertical offset in px before element is first unpinned
		"offset": 164, /* set this to height of your header */

		"classes": {
			// when element is initialised
			"initial": "animated",

			// when scrolling up
			"pinned": "slideDown",

			// when scrolling down
			"unpinned": "slideUp",

			// when above offset
			"top": "headroom--top",

			// when below offset
			"notTop": "headroom--not-top"
		}
	});

});

style.css

@media only screen and (min-width: 1025px) {

	.site-header {
		position: fixed;
		width: 100%;
		z-index: 10;
	}

	.nav-primary {
		padding-top: 164px;
	}

}