How to preserve the value of an old domain when building a new website.

Selected answers from the Dumb SEO Questions Facebook & G+ community.

• 
  Sandra Sinclair: Hi Everyone!
  If building a completely new website - how will that affect my SEO efforts of my previous website? Will all the work go to waste? New site will be on old domain.
  
  Thanks in advance!
  Sandra
• 
  Lori Eldridge: Need more info. If you're building a new website because the old one was penalized, then better build it on a new domain and don't link from the old to the new.
• 
  Citation Gurus: Agreed. Also some templates with content management sites can cause issues even with 301 redirects from all old links so I would try and cross test the 2 first if it is a CMS site to make sure that the new template does not affect the seo. Someone in another group I'm in had this happen to them awhile back after switching to a new template. Then switched back and was fine.
• 
  Will Marler: Yeah, we need more info on this one.
  
  Why the rebuild and, more importantly, 'how' the rebuild?
• 
  Sandra Sinclair: Hi! Thanks for your quick input. My client recently told me they want to redesign the entire website. They are ranking great and never been penalized... They strictly want to do a total makeover of the design...
  
  Just wondering if, and how, this will affect SEO...
• 
  Lori Eldridge: In that case either change the design or the content but not both, otherwise it can cause problems and a drop in ranking. If your client wants both then do one now and the other once you see the site ranking hasn't changed.