What's the best way to phase in a complete site redesign?

[BlueAcorn]

Our client is in the planning stages of a site redesign that includes moving platforms. The new site will be rolled out in different phases throughout a period of a year. They are planning to put the new site redesign on a subdomain (i.e. www2.website.com) during the roll out of the different phases while eventually switching the new site back over to the www domain once all the phases are complete. We’re afraid that having the new site on the www2 domain will hurt SEO.

For example, if their first phase is rolling out a new system to customize a product design and this new design system is hosted on www2.website.com/customize, when a customer picks a product to customize they’ll be linked to www2.website.com/customize instead of the original www.website.com/customize. The old website will start to get phased out as more and more of the new website is completed and users will be directed to www2. Once the entire redesign is completed, the old platform can be removed and the new website moved back to the www subdomian.

Is there a better way of rolling out a website redesign in phases and not have it hosted on a different subdomain?

[YannickVeys]

The way they're planning it now is really, really a bad idea. First you put a part of the new design. New url's start popping up. SE's crawl that, might find duplicate content, you need redirects in place, but what happens when the site is moved again, you have to change redirects again... So it sucks!

You can put everything on the www2 domain, but put a noindex nofollow in the header. Better still would just to let the new website sit behind an authentication screen so only you, developers, etc. can reach it. Once it's fully ready and you know what all the new urls will be, setup redirects (301's!) and once they are ready to go, than move the new site in place.