Do New Windows Need Title 24?
Usually yes. Fenestration is one of the components the Energy Code regulates directly, so replacing or adding windows brings a project into scope even when nothing else changes.
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The numbers that apply
For fenestration in prescriptive additions, the requirement is a U-factor of 0.30, and that figure applies in every one of the sixteen climate zones. Solar heat gain coefficient is capped at 0.23, with an exception: zones 1, 3, 5 and 16 carry no SHGC requirement at all. Those are the cool coastal and mountain zones, where keeping solar gain out is not the problem it is in the valleys and the desert.
There is also a small allowance: up to 30 square feet of fenestration is exempt from the U-factor requirement. That is often enough to cover an awkward feature window without forcing the whole schedule up to a higher specification.
What the values mean when buying windows
U-factor measures heat flow through the assembly — lower is better, and 0.30 is a double-glazed low-emissivity unit rather than anything exotic. SHGC measures how much solar energy comes through; 0.23 is a fairly selective coating. Both are published on the manufacturer's label for the whole unit, frame included, and it is the whole-unit figure the code uses, not the centre-of-glass number that sometimes appears in marketing.
Area matters as much as performance
On additions over 700 square feet, fenestration area is capped at 175 square feet or 20 per cent of the addition's floor area. A design can therefore fail on how much glass it has even when every unit specified meets the performance numbers. Where that happens, the performance path allows the extra glazing to be offset elsewhere — but it has to be modelled rather than asserted.
On a straight replacement in an existing opening, the test is normally just the performance of what goes in. Enlarging the opening changes that, because it changes the envelope.