My Extension End wall question

[Basecoat]

Hi All

I am not sure how this wall (arrowed) in the sketch should be built. From foundation to a height of 2500 its inside wall. Above this height its exposed with a window. My question is how do I build it A) cavity to full height or B) build it solid upto 2500 height then cavity to roof.

I would appreciate your help. Thanks in advance.

 

[masona]

If it was me I would go for solid build, cheaper, quicker & warmer than a cavity walls, More and more properties are now filling their cavity with foam filling cavity for heating saving.

The BCO and the drawing plans will have the final details choice for you to follow, although you should have the choice of input of building materials.