#1346 Cathedral Ceiling Modeling

[Michael Shewmaker]

From Scott's email: 12/23/22, 11:52 - summary of issue
In some of the testing that Mikey has been doing we uncovered some issues associated w/ our rules that transform New/Altered cathedral ceilings in proposed models into attics in standard design models.
The root of the problem is that we are not paying attention to the consistency between the status and slope of cathedral ceilings vs. the status and slope of standard design attic surfaces. If an attic (over conditioned zone(s)) already exists in the model, then we transform cath ceiling surfaces into surfaces of that attic (regardless of attic status or slope) and if no attic exists, then we create an attic w/ default status and slope. So low-sloped, altered cathedral ceiling surfaces are getting modeled in the standard design as new, steep-sloped attic roof surfaces (w/ different requirements).

Concerns from CEC:
The new above deck insulation requirement for altered low-sloped roofs is not being applied when the cathedral ceiling is converted to an attic space w/ default roof slope (5:12), or an existing roof-slope >= 2:12. Additionally, the steep-sloped cool roof requirements (0.20/0.75) are incorrectly being applied, as opposed to the low-sloped requirement (0.63/0.75).

[Scott Criswell]

Actual work here is restricted to roof slope.
References to New/Altered cathedral ceiling & attic status are not valid because the only case (as of 2022 code) that we convert cathedral ceilings to attic is New Construction, where ALL components are New.
Same for CEC concern re: above deck insulation requirement for altered low-sloped roofs - since (EAA) Altered cathedral ceilings are not converted to attics.

Mods/fixes resulting from this ticket will ensure New, steep and low-sloped cathedral ceilings will be converted to attic with consistent steep/low-sloped roof surfaces.

[Scott Criswell]

ruleset mods checked into SVN @ r2440

• separate attics created for steep (>=2 in 12 rise/run) vs. flat to ensure proper std design attic roof treatment
• cathedral ceilings added to proposed attic of same classification (steep vs. flat), otherwise new attics created for std design
• when new attics are created for std design, attic roof tilt set based on area-weighted average of proposed cathedral ceilings' tilt (by classification)