Windows – does CA Title 24 preclude SHGC > 0.30?
user-5691874
| Posted in Energy Efficiency and Durability on
Building in Zone 3 with 3500 HDD, lots of shade in the west and I want to warm the house with the sun in the morning. Planning to use Marvin Integrity windows, and I asked the vendor for low E1 for the east facing windows – but he said “The reason they don’t offer LowE 1 is that it does not meet California Title 24 Energy code requirements for SHGC, which is 40 and needs to be 30 or below.”
Questions:
Does CA Title 24 really forbid SHGC > 0.30?
I’ll be using low E2 (SHGC 0.30) elsewhere, with awnings on south and west. Is low E1 / SHGC 0.40 a mistake on the east windows?
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Replies
See http://www.cardinalcorp.com/technology/applications/energy-calculator/
Bill,
I don't know much about Title 24, but from my online research, it sounds as if there are prescriptive maximums for window U-factor, but no prescriptive requirements for window SHGC. It sounds as if window SHGC only matters when someone chooses a performance compliance path instead of a prescriptive compliance path.
More information here: Windows, Skylights and Title 24.
Needless to say, if I am misunderstanding the situation, I hope that someone who is more familiar than me with Title 24 requirements posts a comment here.
-- Martin Holladay
Bill,
I just found another source: Title 24 Quick Reference Guide.
According to this source, "RSHGC (Residential Solar Heat Gain Coefficient) – Even though this number does weigh in towards the performance and compliance of the over‐all building, there is no performance minimum requirement residentially. Prescriptively zones 1, 3 & 5 are exempt and all other zones are required to have a .25 or better."
If this document is correct, it means that in your case (since you are in Zone 3), your building is exempt from SHGC requirements if you follow the prescriptive approach.
-- Martin Holladay
Make sure to avoid conflating CA climate zone numbers with DOE climate zones (which are never called out in Title 24.)
The map you should be referring to regarding Title 24 regulations is here:
http://www.energy.ca.gov/maps/renewable/BuildingClimateZones.jpg