I think exterior walls need one more layer! EXTERNAL Insulation. It would go outside of the sheathing and inside of the cladding air gap.
And now that I think about it, the air gap could use a bit more detail. The exterior insulation I plan to use recommends 1x3 (nominal) vertical battens outside of the insulation, oriented vertically, centered on the stud centers and spaced same as the studs - and they will also function as the air gap spacer! Not sure what other options there should be.
What about a house wrap layer (eg. Tyvek)?
House wrap, being so thin, is HARD to show in SketchUp - other than as a possible TEXTURE applied to the whatever it’s wrapping.
It’s usually so thin that it can be ignored for dimensioning/take off purposes for the building - unless it’s one of the new ones that incorporates a rain shield under the cladding, in which case it should be another option for the “Air Gap” between sheathing and cladding.
Same is true if you’re putting a vapor or air barrier on the inside of the wall. Actually, even more so because there aren’t variants (that I’m aware of) with enough thickness to model.
My interest is mainly visibility control. If it is on a separate layer, it’s visibility can be controlled easily.
I’ve previously tried to model house wrap - before @Medeek’s extension came out. Even visibility is a problem since, as you zoom away from it, OpenGL starts letting what’s under it bleed through. I got so frustrated that I went with the texture option to simply show it’s presence.
I did try making it thicker than it actually is, but even at 1/32", it was hard to work with and prone to frequent inference problems - if you try to infer to an edge or corner and you’re not zoomed in VERY close, you can easily infer to the wrong point - and if you infer to the inside side on one end of what you’re drawing and the outside side on the other, the plane of what you’re drawing stops being parallel to the other planes in the wall assembly!
All of this, taken together, is why I refrained from suggesting that house wrap be added to Medeek’s extension!
I have tended to avoid modeling things that are extremely thin (ie. house wrap, sill plate foam etc…)
The problem as @sjdorst suggests is one of inference problems and Z-fighting.
Battens and exterior insulation might be in the works though, I’ve had a lot of interest in Battens from Australian builders and designers.