Roof Assembly Definitions in BEopt

asked 2020-01-08 19:40:29 -0600

trevdawg122's avatar

I would like to better understand how roof assemblies are modeled in BEopt. Usually for options the property names and/or descriptions are sufficient, but with roof assemblies I need more information to properly model. Unfortunately I don't have enough Unment Hours points to upload pictures for reference (sigh...), but the building I'm modelling has "unfinished attic" and "finished roof" components because there are vaulted ceilings. If I understand correctly in theory the two should be pretty similar except that an unfinished attic truss will have longer members between the top and bottom truss chords than a vaulted ceiling truss. Without detailed formulas and diagrams I'm not sure exactly how the framing thickness, ceiling joist thickness, roof framing factor, ceiling framing factor are defined. My trusses are made of 2" steel hat channel, mostly 18Ga, and that's for top chord, bottom chord and members in-between. I mentioned in a previous post that instead of worrying my pretty little head about all of this I would instead use cold-formed steel equivalent R-value data in the IRC to guestimate a rough difference in R-value between wood and steel and then increase the framing factor until the assembly R-value is reduced by said difference. I didn't get a response though. Thanks for your time.

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