buck_taylor

Heat travel towards Cold in ALL directions. It doesn't matter the orientation. Hot air rises because it is less dense than cold air. We insulate attics (and floors) with more insulation because it is easy (costs less). More heat escapes through the walls than the ceilings in most structures. The formula is: Surface area x U-Value. There is an orientation component to the air film layer used in U-value calculations (vertical through horizontal), but there is no component in U-value calculations that concern whether a component is part of a ceiling versus a wall. 2x6 walls are structurally stronger than 2x4 walls. 2x6 studs cost more (more material, weight, volume, etc). If you don't need a 2x6 for structural reasons then DON'T use them. A decade ago the nominal cost between a 2x4 and 2x6 was pretty nominal, so it was a pretty easy solution to utilize a 2x6 wall to meet the energy codes. The IECC Energy codes look at the thermal performance of the wall assembly. A 2x4 wall with a continuous rigid foam insulation layer (inside or out) has a lower U-value than a 2x6 wall with just cavity insulation. The IECC Building code covers structural requirements. You as the designer (or builder) must design the building to meet both components of the code. I would suggest anyone reading this start looking at the IECC2021 codes, and play with the corresponding (web-only currently) version of ResCheck to get an idea of what's to come with a much bigger emphasis on building assembly U-values. IECC Codes ResCheck

Did you try the ceiling plane tool in the roof planes toolbar? You draw a manual ceiling plane above the loft and use its property page to match the slope of the adjacent ceiling.

Update: looks like the floor area is calculated from the surface of the sheetrock, while the ceiling is calculated from the face of the framing. The walls appear to be a combination. Got a few more configurations to try and confirm. @lbuttery- yes this would be a good option to have in a preference or configuration to allow the user to select the appropriate surface. It is awkward to explain to an observer why there is a difference.

How does Chief calculate thermal areas that are exported? I created a 21' x 21' square building, standard 2x6 walls, and a 10' finished ceiling. When I export to ResCheck I get the following areas: Walls: Gross area 201 ft. Floor: 399 ft. Ceiling: 403 ft. The window and door areas are correct. This is a simple example, but I do a lot of mechanical design and energy compliance work on larger complex homes and these seemingly small errors can add up. The expected floor area and ceiling area should be 400 sq.ft. each. There is no reason for a difference. The expected wall surface area should be 200 sq.ft. each wall. Why the extra foot? What I'm asking is what reference is Chief using when defining a space or thermal boundry? For heat loss, the thermal envelope starts with the first surface you encounter, so technically it would be in the inside surface of drywall for walls and ceiling, and floor finish for the floors.