on the project I am working on, they want the web application to have the header, sidebar and footer remain fixed in the browser. So only the content area will scroll. I don't think this is a good idea because it breaks user expectations of how web-based things work, but I'm looking for more evidence to present. Any ideas?
It's usually a bad idea because the header, footer and sidebar are ancillary to the primary content area. Why take screen real estate away from the primary function? There may be a reason, and, if so, consider it, but usually the request is arbitrary, at best. Have you asked why they desire that?
There are compromise solutions as well. Instead of a full footer, perhaps they could use a small tool-bar (ala the old Facebook footer) for example.
I think there's absolutely nothing wrong with it. In many cases, the richer the application, the closer it will be to a desktop app, and the less it will be restricted by standard web page behaviors. Consider Grooveshark, Google Maps, Docs, Calendar and Reader for examples of apps where only the content area scrolls. And that's just from the tabs open in my browser right now :)
I see @Vitaly's point but in those cases, "Grooveshark" for example, the footer is a controller in which you perform regular activities throughout the time you stay on the site.
This wouldn't make any sense if the footer would only contain links or text. I think the questions here are:
What is the content of such footer and header?
How much will user be using them?
How relevant is the information contained therein?
Why do the managers want to keem them fixed? What functional requirement does it addresses?
You sould take into account that if what the user is looking for is the content per se, and the footer/header are rather big, then the user would find himself scrolling in a tiny space getting informatin bit by bit which would make the whole experience really uncomfortable.
But if, in contrast, the user will be interacting with the header/footer on a regular basis, then having them fixed on the browser might not be such a bad idea.