Vulcan Vents offers a wide variety of vents, for both new install as well as retrofit over existing vents, as the one in these photos show.

David had all the vents in their home retrofitted, including foundation vents, under-eave vents and soffit vents above an alcove.

Recommended by: David at 261 S Castanya

Installed by:  we are not recommending our installer, who is also no longer a vendor of Vulcan Vents

Manufacturer:

Vulcan Vents @ vulcanvents.com

Installers: 

For standard size vents, a handyman (yourself?) can easily install these vents.  Nigel Ray installed his!

The following is the installer recommended by Vulcan Vents, and who services Portola Valley:

McDermaid Preservation and Restoration @ mcdermaidpainting.com