Does duplicate content on a sub-domain affect the rankings of root domain?

[Amjath]

We recently moved a community website that we own to our main domain. It now lives on our website as a sub-domain. This new sub-domain has a lot of duplicate page titles.

We are going to clean it up but it's huge project. (We had tried to clean it even before migrating the community website)

I am wondering if this duplicate content on the new sub-domain could be hurting rankings of our root domain? How does Google treat it?

From SEO best practices, I know duplicate content within site is always bad.

How severe is it given the fact that it is present on a different sub-domain?

[Daylan]

A subdomain site is treated as a different website than that of your root, but having a large amount of duplicate content (being a forum, I am assuming it does) can't be great. Is there any reason to keep the two operating at the same time (and not just 301'ing it)?

The old site would still be getting crawled and indexed so from an SEO perspective i guess that's a bad factor for your root domain as it'd be a direct competitor against your proper domain content.

Your best bet would be to either cannonical the content on the old domain/posts and/or 301 the old stuff to the new stuff as soon as possible. From both a user point of view (2 sites isconfusing) and a duplicate content point of view. I guess the main issue would be that you now have yourself as a competitor for content that should be getting found from your main domain.

[Amjath]

Hi Dylan,

Thanks for the reply. The community website does not exist anymore as a standalone website. It is now a sub-domain on our main website.

e.g. Before -

we had www.mainwebsite.com and www.communitywebsite.com

After -

we have http://community.mainwebsite.com

And this sub-domain has thousands of duplicate page titles.

Will that affect www.mainwebsite.com?