Easy One - Do my loft walls have a cavity?

[Kalibre46]

This may sound like a dumb question, but I'm trying to work out final interior spaces for a potential loft conversion. My house is detached (1950's) with a gable end on both roof aspects.
When I look in my loft at each end I see red brick construction. Is this the internal skin of a cavity wall or are the outside walls of lofts just single skin with the cavity starting on the floor below? I'm thinking it's the latter, but thought I'd check with the people in the know! Thanks.

 

[noseall]

The cavity wall typically carries on up within the roof space.

 

[Kalibre46]

Many thanks!

 

[tony1851]

Sometimes the party wall is solid (9") brick.
Uusally the outer gable wall is cavity, continued up from below.

Why are you so concerned about dimensions at this stage? However 'accurately' you work it out on paper, it will end up different as-built.