The mansion is located at 1807 Latigo Canyon Road, Malibu, California, USA.
Various independent film companies shoot many low-budget films there, not just the 1313 homo-erotic series by David DeCoteau. Many other softcore sex comedies and dramas as well ('Barely Legal' is one of them). I'm heard that David DeCoteau used to rent it out by the owner who lived in a small room on the third floor and used to use it to rent it out on a regular basis for film crews.
Go to web sites such as Zillo, or Trulia, or Malibu realator sites and check it out and who currently owns it now.

I saw some Cinemax softcore porn that was filmed there. They must rent it out.

Yeah but to hire mansion like this costs at least 10k/day so I doubt he rented it. Most likely one of his friends owns it. He knows many people in the brand so I guess It's not that hard for a filmmaker like him.

I don't know if it's his friend's mansion or not, but Los Angeles is full of mansions and big houses like that that are available to rent for filming.