Hey Christine,
It’s not slowing down your site in any appreciable way. You may have a suggestion in a performance review for that, but it’s not going to slow down the drawing of your site by the browser.
What those attributes do is reserve space for an image. Your logo is so small both file size and dimension wise that it will be there as soon as the page is visible to your visitors.
If you really want to add them though you can. First edit your header.php file.
This section is for the logo:
<div id="logo"><?php
if (is_front_page()) {
echo '<h1><a href="'.home_url().'/"><img src="'.of_get_option('logo','').'" alt="'.get_bloginfo('name').'" /></a></h1>';
} else {
echo '<p><a href="'.home_url().'/"><img src="'.of_get_option('logo','').'" alt="'.get_bloginfo('name').'" /></a></p>';
}
?>
</div>
You can add the height and width of your image logo to the two image tags there.
The home block ones are background images on desktop sized displays. If you want to add the height and width for the smaller screen version you can. Edit the page-home.php file. The calls to those images look like this:
<img src="<?php echo of_get_option('section_image_6'); ?>" alt="" />
Feel free to add the sizes to those too.
Take care,
Bill