How to read and use TABLE SB 5.5-5–2017 (OBC SB-10)

[sunyaer]

The following table is from OBC SB-10:

TABLE SB 5.5-5–2017 (See Appendix A.)
(Supersedes Table 5.5-5 in 2013 ANSI/ASHRAE/IES 90.1)
Building Envelope Requirements for Climate Zone 5 (A, B, C) (SI)

Opaque Elements Nonresidential Residential Semiheated
Assembly Insulation Assembly Insulation Assembly Insulation
Max. U-Value Min. RSI-Value Max. U-Value Min. RSI-Value Max. U-Value Min. RSI-Value

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Questions:

1. This table is tilled as "Building Envelope Requirements", while in the column "Opaque Elements", roof, mass, floors, and slab-on-grade floors are listed, are these elements building envelope? Why are they listed in the table?

2. What does "Opaque Elements" refer to?

3. What does "mass" refer to in the table?

4. Is there a simple sample showing how to use this table? Or a few simple steps for its application in design /inspection?

 

[tmurray]

1. Yes, they are part of the building envelope. They are broken out to allow different styles of construction to meet different thermal resistances.

2. Codes generally differentiate requirements for opaque components of a building with fenestration.

3. Mass refers to systems that are mostly one building material.

4. Table use is very simple. If I have a non-residential structure and lets say I want to look up how much insulation I need for a wood framed wall, I just find the appropriate categories and I see that I can do a wall with a U-value of 0.261 or 2.3 RSI cavity insulation and 1.8 RSI continuous (out-of-board) insulation. The U-value allows designers to calculate their own assembly using isothermal planes and/or parallel heat flow calculations. The RSI is more for people who just want to quickly select materials.

 

[sunyaer]

1. Yes, they are part of the building envelope. They are broken out to allow different styles of construction to meet different thermal resistances.

It's easy to understand that slab-on-grade floors are building envelopes, like house basement floors. What about elevated floors as building envelopes? Would a scenario be an example where an office building with parking garage floors as open (unheated), the lowest floor slab separating the heated floors from garage floors is considered part of the building envelope?

 

[tmurray]

It's easy to understand that slab-on-grade floors are building envelopes, like house basement floors. What about elevated floors as building envelopes? Would a scenario be an example where an office building with parking garage floors as open (unheated), the lowest floor slab separating the heated floors from garage floors is considered part of the building envelope?

Absolutely. Anything that is either unconditioned, partially conditioned, or exterior. Certain energy codes will allow slightly lesser insulation levels for assemblies separating conditioned and partially conditioned spaces, so be on the look out for that.

 

[sunyaer]

In the table, there are values like: "1.8+3.3", "4.4+1.9Ls", "2.3+3.3ci". I know Ls=liner system, ci=continuous insulation, but how to read those values with "+"?

 

[tmurray]

The first number is the cavity insulation. The number after the plus is the out-of-board insulation.