[Equest-users] slab on grade answer

[Patrick J. O'Leary, Jr.]

i just received a clarification about the f-factor for 4" slab on grade 
vs 6" slab on grade for the purposes of leed review.  the usgbc response 
(through the website/contact section) is:

"Thank you for your technical customer service inquiry regarding LEED-NC 
v2009: EAc1.  It is assumed that you are following the Performance 
option (Option 1) of EAp2 & EAc1, using Appendix G of ASHRAE 90.1.

Yes, the 4" slab (modeled & specified) should meet the requirements for 
LEED purposes.  Please note that there is no F-factor requirement listed 
as part of the Mandatory provisions of Section 5.4; it is only listed 
for the Prescriptive approach requirements of section 5.5, which is not 
necessary for LEED EAp2/EAc1 compliance.

If you model the slab as a 4" slab with 12" of earth (0.75 soil 
conductivity) underneath it in the Proposed Case model, the energy model 
should indicate the U-value of this slab.  You could simply state in 
your submittal (4" slab modeled with 12" of earth with 0.75 Btu/h-ft-° 
soil conductivity, U-value calculated within energy model as x.xx).  
Please be careful to avoid the common mistakes of modeling the slab 
without any earth beneath it, or modeling the Baseline slab "U-value" 
using the "F-factor" values from Tables 5.5-1 - 5.5-8.  F-factors and 
U-values are not interchangeable, of course.  Also, if the energy model 
cannot reflect an F-factor, please model the Baseline slab-on-grade 
floor as a 6 inch concrete slab over earth with a soil conductivity of 
0.75 Btu/h-ft-degree F, in accordance with A6.1.

We trust that this will help you with your process and we thank you for 
your interest in LEED Rating Systems.

If you have any further questions, please feel free to contact us via 
the GBCI contact page: http://www.gbci.org/contactus.

Regards,

<name redacted>
GBCI Technical Customer Service
Green Building Certification Institute
2101 L St. NW . Suite 500
Washington DC 20037
800.795.1746 . fax 202.828.5110
WWW.GBCI.ORG

The text above represents a staff opinion on a particular issue, and 
does NOT set any precedent to be upheld during a LEED Certification 
Review. For official rulings in advance of a LEED Certification review, 
customers should utilize the formal inquiry process available in LEED 
Online. Applications for LEED Certification will be thoroughly reviewed 
based upon the LEED Rating Systems balloted & approved by USGBC Members, 
applicable Addenda, USGBC-approved LEED Interpretations, and Project 
Credit Interpretation Rulings (CIRs) administered by GBCI, as 
applicable. Please note that certain inquiries submitted to USGBC are 
forwarded to GBCI for reply, as appropriate."

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