I'm building a 1400 sq. ft addition which will be mostly covered with a flat (very low sloped) roof, with a second storey bedroom over the rest.
I'd like to have 4" of continuous rigid exterior insulation (in addition to cavity insulation), so to keep my overall wall thickness down, I'd like to have the walls framed with 2x4s. My architect said that because of the 10' high walls they would need to be framed with 2x6's (according to Ontario building code), but I'm nearly certain I've seen recent builds that have 10' high walls that were framed with 2x4's.
I've not been able to specifically find anything to prove/disprove this yet.