Any experts in Title 24, Part 6 out there?
In replacing a wall and adding insulation (home was built in 1961 and currently has no wall insulation) I am also adding two small windows to this south-facing wall. Because I’m adding windows, I need to comply with either the prescriptive requirements of Title 24 or the performance requirements. Because I’m not adding conditioned space, I cannot demonstrate performance based only on the new space, but would have to demonstrate it on the whole house which is completely impossible without a gut remodel.
The prescriptive requirements for California Zone 12 (unrelated to DOE zones) requires a SHGC of .25 or “better.” I can do that and comply with the prescriptive standards, but I’m pretty sure it will actually make my energy consumption higher than if I were allowed to buy the windows with similar U-factor and higher SHGC that I prefer. I have massive heating bills in winter and run my air conditioner for perhaps 10-15 hours per YEAR. Cooling is a total non-issue because my house is in a zone considered to be warm, it is actually in the bottom of a valley and is well-shaded by nearby hills and trees. I also open screened windows at night and keep them closed during the day. This combined with closing window coverings to keep heat out is enough to keep my house comfortable enough for us, except during the 15-20 hours per year that I mentioned. The sun will not shine significantly on these south-facing windows during the summer because of a modest roof overhang. It does shine on these windows (during the hours when the hills aren’t shading the house during the winter. So, I’d like to get as much solar heat gain through these windows as I can to the extent this doesn’t require lowering my u-factor. I have found two windows with U-factors that meet the U-factor requirements and have quite different SHGC numbers, one of which is what I want and the other complies with the prescriptive requirements under Title 24.
There’s no way I can legally do this, is there? Am I right that the reality that this house doesn’t suffer from excess heat gain just doesn’t matter and I must comply with the prescriptive standard for my zone, unless I can comply with performance standards for the whole house (which is totally impossible)?
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That should say: "Cooling is a total non-issue because, WHILE my house is in a zone considered to be warm, it is actually in the bottom of a valley and is well-shaded by nearby hills and trees."
Domenico,
There have been several similar issues in the past related to code requirements for low-solar-gain windows. As you correctly point out, orientation-specific glazing often makes sense, and high-solar-gain glazing is often a good choice for south orientations. Not all code officials understand this.
You have described your dilemma well. As a first step, I would approach your local building department and ask to speak to a code official or supervisor. Local code authorities have broad authority to approve features that may not comply with the letter of the law, and you may find the ear of an intelligent, sympathetic code official.
Thanks, Martin. Our Title 24 out here is pretty prescriptive, but ultimately the AHJ decides whether to issue the permit, I'll do what you suggest on the "can't hurt to ask" theory. Maybe I'll get lucky. If not the windows aren't big enough that their SHGC will make a big difference, so it won't kill me to follow the rules, even if I think they provide a perverse result in my case.