Zone 4B – 2012 IBC and SHGC
The new 2012 IBC adoption in my future building area will mandate that windows can only have a maximum of 0.40 SHGC, including the south facing windows. I am trying to achieve a Passive House design but the low SHGC mandate makes it more difficult. I am going with Intus uPVC triple pane windows. Originally I was going to go with the 0.49 SHGC for the south elevation but now I have to go with the 0.37 SHGC. The building department will NOT budge on this factor and will not allow any windows > 0.40 SHGC.
I believe this is where the new code fails by not recognizing a Passive Solar design for a Zone 4B climate.
For the one east window and the two west windows (required by code for fire escape), I will have a 0.25 SHGC to prevent any summer time heat gain.
Has anyone else run across this problem with the new 2012 IECC/IBC?
One possible solution is to add another window or windows on the south elevation to compensate for the lower SHGC?
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Replies
When I read your question, I realize that there are benefits to building a house where I don't even need a building permit.
Could you get Intus to mislabel the windows?
Peter L,
If you want to use windows with a higher SHGC than is permitted by the prescriptive tables, then (as far as I know) you can always used an alternative path -- specifically, the simulated performance path in Section 405. Of course, you'll have to hire an energy consultant to perform the required simulations.
While the simulated performance path option includes restrictions on maximum SHGC for windows in Climate Zones 2 and 3 (see http://www.resnet.us/uploads/documents/conference/2012/pdfs/Barcik-Energy_Code-IECC2012_vs_2009IECC.pdf), I don't believe that there are such restrictions for Climate Zone 4.
Add a low e coating, there are a lot of types some manufactures have it in their u-value, or tint, both can keep the same low u value, not affect light transmission and lower SHGC.
Terry,
I think you misunderstood the question. I don't want to LOWER the SHGC, I want to INCREASE the SHGC on the south elevation. The "low-e" coating would reduce the SHGC which is what I do NOT want.
"Originally I was going to go with the 0.49 SHGC for the south elevation but now I have to go with the 0.37 SHGC. The building department will NOT budge on this factor and will not allow any windows > 0.40 SHGC"
Probably wouldn't hurt to provide a little more info on your design, why and what differene the - 3 SHGC would make to your original .49....sound like you are wanting a lower SHGC by 3 and not increase the glazing area. Looking at 12 IBC I could not find the disclaimer IRC has in it that the combined SHGC is acceptable, and the 15% fenestration are exempt did you? If you are using mass effect and can load it with more area do it if a 3 gain will make an effect on heat capacity and internal dynamics which I doubt.