Hi all-
A quick, but kind of hazy question for me at least, regarding LEED projects. Let's just say, that a building is composed of multiple wall types, spanning a range of the ASHRAE 90.1 definitions...some portions of the building is steel framed, another portion is mass wall, and yet another portion is wood framed, for example. In this case, what would the baseline be defined as? Does each wall remain categorically intact, and you simply choose the baseline U-factor that corresponds to that wall type, or do you have to determine the wall type that makes up the majority of the proposed building, and choose this wall type as the baseline wall type?
Thanks in advance,
Chien
Hi Chien Si !!
I believe you need only put in the one ASHRAE 90.1 minimum wall U-value.
Exactly what Table 5.5 asks for.
John R. Aulbach, PE, CEM
Chien,
Have a look at Table G3.1 in ASHRAE 90.1-2004. As far as I can tell, above-grade walls in the baseline case are to be modeled as steel-framed using the assembly maximum U-factor from Tables 5.5.
Regards,
Brian Tysoe M.Sc., LEED AP
In Table G3.1 (#5 Building Envelope) of 90.1-2004, it says that:
?Opaque assemblies...shall conform with the following common, lightweight
assembly types and shall match the appropriate assembly maximum U-factors in
Tables 5.5-1 through 5.5-8:
* Roofs ? Insulation entirely above deck
* Above grade walls ? steel framed
* Floors ? Steel joist?
So every baseline wall should have the assembly max U-factor for a
steel-framed wall. This also allows credit to be taken for having mass walls
in your proposed design.
All,
There is likely some confusion due to two statements in the LEED Reference Guide:
* On Page 177, under "b. Opague Assemblies" the reference guide states "The Performance Rating Method specifies the type of assembly required for the Baseline Building wall, roof, and floor construction. The ECB method varies the construction assembly type modeled in the Building Budget Design based on the actual construction assembly type modeled in the Proposed Design."
* On Page 180, under "Building Envelope" the reference guide states "The Performance Rating Method requires that the Proposed Design be modeled as designed with a few minor exceptions. For the Baseline Design of new buildings, the above-grade walls, roof, and floor assemblies must be modeled using light-weight assembly types (i.e., steel-framed walls, roof with insulation entirely above deck, and steel-joist floors), with ASHRAE Std. 90.1 prescriptive maximum U-factors for the building's climate. Even if the Proposed Design incorporates mass wall construction, the Baseline Design must be modeled using a steel-framed assembly:"
Obviously, the reference to the ECB Method on page 177 causes some confusion to the reader. However, I read that all building baseline constructions should use a light-weight, steel-framed construction per the statements on page 180.
Regards
Mitchell J. Dec