Subdomains Best Practices for SEO

You often have to use sub-domains or sub-directories on your website for various reasons, including implementing international SEO (search engine optimisation), structuring your site for large number of products or multiple brands, etc.

After setting up multiple sub-domains, you can implement separate SEO strategies (including link building) for each subdomain on your site, without any sub-domain affecting others.

What is a Sub-domain?

A subdomain is an add-on to your domain name. If your domain is:

example.com

An example of a sub-domain can be (if you are to set up a blog on your site):

https://blog.example.com/

What is a Sub-directory?

When setting up a blog on your website, an example of a sub-directory can be:

https://www.example.com/blog/

Topics that are included in this Sub-domain Best Practices for SEO article:

• Sub-domains vs Sub-directories
• When to Use Sub-domains for Websites?
• When to Use Sub-directories for Websites?
• Best Practices When Setting Up Subdomains for SEO
• International SEO
• Multiple Brands or Multiple Product Categories
• Backlink Dilution
• Keyword Dilution
• Conclusions

When launching a new website, or maintaining an existing site, you may set up multiple subdomains or multiple subdirectories.

Subdomains

Sub-domains, such as:

www.example.com
blog.example.com
forum.example.com
members.example.com

Subdirectories

Sub-directories, such as:

www.example.com/blog/
www.example.com/forum/
www.example.com/category-1/
www.example.com/category-2/

The common questions for SEO and/or website development are:

• When to use sub-domains?
• When to use sub-directories?

When to use Sub-domains?

Sub-domains are used when your business and/or website is already in (or is growing very quickly into) a relatively large scale.

Set up multiple sub-domains if you are under one of the below cases.

Case 1

Your website requires setting up multiple languages with international SEO. For example:

en.example.com
jp.example.com
de.example.com
zh-hant.example.com

Case 2

Your website consists of an eCommerce site and a blog. You have separate project/operation teams who will manage and grow the different sub-domains with different digital marketing and/or SEO strategies.

Case 3

Your eCommerce website or business service site offers a large number of products under only a few very distinctive categories. You can set up each category under one single sub-domain. You can implement different online marketing and/or SEO strategies on each sub-domain.

Case 4

When you are working on a website revamp project, you may need to stage or test your new website before hosting your new site on the root domain, you will set up your staging / test site on a sub-domain, such as:

https://test.example.com

When to use subdirectories?

Setting up any new or additional subdomain should be treated as a serious strategic decision in terms of:

• SEO (search engine optimization)
• Maintenance of websites

The best practice is that a website should often be kept on a single domain and multiple subdirectories, unless you have very good reason to set up multiple subdomains.

Other reasons to keep things simple and use only subdirectories:

• You can focus all your website’s backlink building efforts on a single domain.
• After only building all the backlinks to one domain, it makes it easier for your site to organically rank in Google’s SERP.

Before setting up multiple subdomains on your website, we will explain the subdomain SEO best practices with the cases below:

• International SEO
• Multiple Brands or Multiple Product Categories
• Backlink Dilution
• Keyword Dilution

With international SEO, it means your website(s) will be used by audiences/users in:

• Multiple markets / regions / countries (such as USA, UK, Hong Kong, Japan, etc), and or,
• Different languages (e.g. English, French, Japanese, Traditional Chinese, etc)

When implementing international SEO, you can set up your site with one of the three solutions.

• Subdomains
• Subdirectories
• Top-level domains (TLDs)

Solution 1: Subdomains

You can set up your website for international SEO with multiple subdomains, such as:

en.example.com/ (English)
fr.example.com/ (French)
jp.example.com/ (Japanese)
zh-hant.example.com/  (Traditional Chinese)

The pros when setting up your website with sub-domains include:

• Relatively easy to set up
• Allows setting geotargeting in Google Search Console
• Allows different server location per subdomain
• Easy separation of sites (i.e. Each subdomain can be a separate site)

Solution 2: Subdirectories

Set up all the country-specific and/or language-specific sites under the root domain (i.e. www) but with multiple directories.

For example:

www.example.com/en/ (English)
www.example.com/fr/ (French)
www.example.com/jp/ (Japanese)
www.example.com/zh-hant/  (Traditional Chinese)

The setup of your website on multiple sub-directories is easy, but will require adding hreflang meta tags on each page to distinguish among different languages/countries, such as:

<link rel=”alternate” href=”https://www.example.com” hreflang=”en-us”>
<link rel=”alternate” href=”https://www.example.com/fr/” hreflang=”fr-fr”>

Solution 3: Top-level domains (TLDs)

Set up completely separate websites for all the different markets/regions/countries.

For example:

https://www.example.co.uk (English for UK)
https://www.example.fr (French for France)
https://www.example.co.jp/ (Japanese for Japan)
https://www.example.hk/ (Traditional Chinese for Hong Kong)

This is the most expensive setup, as you will have to buy/register a domain name for each market/country.

Case 1

A booking engine offering flight tickets, hotel reservation, and cruise tickets have three distinctive product categories, and can set up each product category on a separate subdomain.

For example:

flights.example.com
hotels.example.com
cruises.example.com

Case 2

When a business offers multiple brands to consumers, it may involve the daily work of more than one marketing team.

Each brand can be set up on a separate subdomain, such as:

brand1.example.com
brand2.example.com
brand3.example.com

This way, each marketing team can be responsible for all marketing of a single domain.

Sub-domains can suffer from dilution of backlinks.

For example, you have your main site is on the root domain:

www.example.com

And your blog site is hosted on subdomain, such as:

blog.example.com

If you received from backlink pointing to your blog site from an external website, this backlink will contribute towards your blog site’s Google organic SERP ranking.

But this backlink will not directly help boosting the main site with Google SEO ranking.

The solution to backlink dilution is to get one set of  backlinks pointing to your main site, and acquire another set of backlinks linking to your blog site.

Sub-domains can suffer from dilution of keywords.

Again, your main site is hosted on:

www.example.com

And you have set up your blog site on this subdomain:

blog.example.com

The blog site will have an advantage to rank organically higher in Google with keywords (keyphrases) that contain the blog word, such as:

SEO blog
XYZ blog
[brand name] blog
[product name] blog

The main site will have no direct advantage on organic ranking within Google’s SERP for keywords (or keyphrases) containing blog.

The best practice is to work on ranking main site and blog site for different sets of keywords.

• The main site (if it is an eCommerce site) can optimize organic ranking for commercial keywords.
• The blog site can optimize Google SEO ranking for question keywords.

The best situations to set up multiple subdomains on your website is when:

• Setting up international SEO for your site.
• Separating the marketing of multiple brands.
• Separating the operations of multiple but very distinctive product categories.
• Setting up a staging site for testing before rolling out the site for live.

Web traffic, SEO best practices & algorithms:

• Mobile SEO Best Practices
• Local SEO Best Practices
• YMYL Sites
• Hong Kong Search Engines

SEO tools:

• Bing Webmaster Tools Tutorial
• SEMrush Tutorial
• Ahrefs vs SEMrush
• Google Search Console Tutorial
• Google Keyword Planner Tutorial

WordPress website development:

• Install WordPress
• OceanWP Theme (for WP Sites)
• Woocommerce Setup Tutorial