Hi,
We are a UK-based consultancy, working on LEED for a mall, and we have a bit of trouble interpreting some of the terminologies & requirements of ASHRAE Tables 5.5 for Building Envelope. Three main questions here:
1) Slab-on-grade floor: Does this mean only the building perimeter that is connected to the earth at grade level? Is this what requires insulating (with either vertical or horizontal insulation) or do we need to insulate the full floor at grade level?
2) Linked to above, the Mall has 2 floors of unconditioned underground parking (which are only ventilated). Do we need to insulate the floor above the upper parking level? If yes, which criteria do we need to meet, those of the "slab-on-grade floor", or "floor"? Should this be considered "semiheated"?
3) The atrium skylight in the mall has an area larger than 5% of the total roof area, however Ashrae only mentions the limiting U-values for up to a 5% skylight. What do we do in this case? Do we still use the upper level limits, or is there another section in Ashrae that deals with exceptions?
These questions may sound basic for US architects/engineers... but the regulations are different in Europe!
Many thanks,
Maya
Roger Chang
Principal, Energy and Engineering LeaderDLR Group | Westlake Reed Leskosky
LEEDuser Expert
398 thumbs up
April 1, 2010 - 8:36 am
Maya, do you have access to the 90.1 user's manual? This manual provides very good guidance (with diagrams) for building envelope requirements and provides much more detailed descriptions on how to comply.
1) Slab-on-grade: just what's on Earth. You have to provide insulation at the edge for some climate zones.
2) You do need to insulate the floor above the parking level. Those requirements are based on the "floors" section of Table 5.5, rather than "slab-on-grade." Consider this nonresidential, rather than semiheated.
3) When you exceed 5% skylight to roof area, you have to demonstrate compliance using either the trade-off method or whole building energy simulation. For the trade-off method, you can use Comcheck (http://www.energycodes.gov/comcheck/ez_download.stm), a program developed by the Department of Energy. You're most likely going to need to do whole building simulation for your project to meet EAp2.
Maya Karkour
EcoConsulting871 thumbs up
April 1, 2010 - 10:14 am
Many thanks Roger, this is very helpful.
Does the same reasoning apply to the insulation, i.e. could we just do the whole building simulation without meeting the limiting U-values? My understanding is that it is not the case, as LEED EAp2 specifically requests meeting the mandatory provisions of section 5.4.
Thanks
Roger Chang
Principal, Energy and Engineering LeaderDLR Group | Westlake Reed Leskosky
LEEDuser Expert
398 thumbs up
April 1, 2010 - 11:47 am
For opaque assembly U-values, you do need to provide the minimum amount of insulation called for in Table 5.5 as per section 5.4.1. This is a great observation actually, as I've seen some people assume that whole building simulation allows any U-value to be used.
Christopher Schaffner
CEO & FounderThe Green Engineer
LEEDuser Expert
962 thumbs up
April 17, 2010 - 3:26 pm
Roger - I disagree. Section 5.4.1 references 5.8.1.1 - 5.8.1.9, which covers things like insulation labeling. Table 5.5 only applies to the prescriptive envelope option. If you are running a model, you could, in theory, put in less insulation and still comply.
Gustavo De las Heras Izquierdo
LEED Expert181 thumbs up
December 3, 2019 - 6:04 am
Hi Christopher, I agree with you.
The Energy Cost Budget Method allows trade-offs between systems, as long as the proposed
building’s annual energy consumption remains below that of a reference building that meets
minimum requirements. The way I read the Standard, a more efficient mechanical system can compensate
for a building envelope that does not meet the prescriptive requirements.