Accent Window Systems
Title 24 and Low-E Glass, Explained
Most people find out Title 24 applies to them at the worst possible moment. Here's what it actually asks for.
Current as of 2026-09-19.
Yes, it applies to a replacement
A common misunderstanding: people assume California's energy code is a new-construction problem. Title 24 is that code, and the requirements keep getting stricter. Homeowners are usually unaware it applies to a replacement.
In practice, fenestration alterations must meet the U-factor and SHGC targets for your climate zone. A like-for-like retrofit in San Jose may not need a building permit, but the glass still has to perform. Full-frame work, framing changes, and other cities often require a permit — and the inspector will look at the labels on the units we install.
What Low-E glass actually does
How Low-E works: it reflects heat back to its source. On a dual-pane unit the four glass surfaces are counted from the exterior inward. A coating on surface 2 reflects summer solar heat back out before it enters the house. A coating on surface 4 reflects interior heat back into the room in winter, which is why surface-4 coatings have become common as requirements tightened.
On South Bay jobs we most often specify dual-pane Low-E packages that hit Climate Zone 4 targets. When the opening faces heavy sun or the code path calls for it, we add the fourth-surface coating so summer heat and winter loss are both covered — without guessing at the counter.
Sixteen climate zones
California is split into sixteen climate zones and the requirements differ by zone. Naming the zone for this service area is what makes the page local.
Accent's South Bay service area — San Jose, Los Gatos, Saratoga, Campbell, Cupertino, Santa Clara, Willow Glen, and Almaden — falls in Climate Zone 4. That is the baseline we use when we specify glass for your openings.
What this means for your job
- We specify the compliant unit for Climate Zone 4
- Product labels and docs travel with the install
- Permit path depends on city and scope — we say which before you order
Accent provides the Title 24–ready product documentation. The contractor or homeowner pulls the permit when the city requires one; we make sure the glass on the truck matches what the paperwork claims.
Do I need Title 24 compliant windows for a replacement?
Yes when the replacement falls under California's energy code for alterations — which is most permitted window work and many full-frame jobs. Even where a city like San Jose skips a building permit for a like-for-like retrofit, the glass still needs to meet current U-factor and SHGC targets for your climate zone. We specify so the units pass inspection.
What does Low-E actually do?
It reflects heat back toward wherever the heat is coming from. In summer that means pushing solar heat back outside before it gets into the room. In winter it means pushing the heat you've paid to generate back into the room instead of letting it out through the glass. It's a microscopically thin metallic coating on a specific face of the glass, not a tint, and you won't see it.
Why does the surface the coating is on matter?
Because it changes which direction the heat gets sent. A dual-pane unit has four glass surfaces counted from outside in. A coating on the second surface handles summer heat coming at the house. A coating on the fourth surface handles winter heat trying to leave it. As the code has tightened, more units carry both.
Which climate zone am I in?
San Jose, Santa Clara, Cupertino, Campbell, Saratoga, Los Gatos, Willow Glen, and Almaden sit in California Climate Zone 4. Requirements for U-factor and solar heat gain are set by zone — Zone 4 is the South Bay baseline we specify against.
Will more efficient glass make my house darker?
Modern Low-E is engineered for clarity, not tint. You keep the view; you lose the heat gain you do not want. If a room already feels dark, we talk about glass package and opening size together rather than assuming efficiency means gloom.
Who handles the paperwork?
We specify compliant units and provide the NFRC labels and product documentation the inspector expects. On contractor jobs the GC typically pulls the permit; on residential work we tell you what your city requires and help coordinate so the paperwork matches the glass that lands on site.
Ask about your project.
Bring the opening. We will say what the code asks of it.