How to get Header not to reload on every page?

I’m testing a new custom theme, where there’s a page load issue regarding the Header that is a bit annoying….

I noticed that when visiting any page on the blog, the blog’s logo first appears under the content, then when the Header fully loads every thing is pushed down. I understand why it loads like this, but it gets annoying when you navigate around to multiple pages. Is there any way to make the height of the header remain static even when it hasn’t finished loading yet? Perhaps a Cache issue or setting a defined Height or something to the Header? I don’t notice this problem with any other blog so I’m sure there’s a solution.

You can see it here –> https://67.192.53.165/dataatrisk/

Thanks!