Shooting on Location vs Set
One of the advantages of shooting on a location rather than a set is question of scale and a question of period. We go primarily to locations for its exteriors, for the look of it, and how it sits in the countryside. Or the countryside itself. That we just can’t recreate in the studio.
So, when Jamie takes a journey to Helwater, which is an English stately home, he’s now in what’s known as the “Lake District,” the border countries of England. We’re looking at a great stately home and we just can’t build that exterior on a studio. So, we have found those locations and they give us a grandeur. They give us a scale. And they give us the right setting to put Jamie in that story in. In this particular, all of the interiors and exteriors were shot on location. That’s one of the great adventures about Outlander for us as a production—that each episode is different. Each story presents new challenges.
~ David Brown, Producer
The fictional houses of Helwater and Ellesmere Manor were a made up of a combination of two of the finest stately homes in the south of Scotland with elements of each real house in both fictional homes. As many stately homes were modified by successive generations, they provide a rich supply of locations options. We have shot both these stately homes from another different side in previous seasons, but you would never know.
~ Hugh Gourlay, Supervising Location Manager
Ellesmere Manor

Source: Outlander Community