What the 2025 Energy Code changed for homes

The 2025 Energy Code applies to every residential permit application submitted on or after 1 January 2026. If you are building a house, an ADU, an addition or a remodel in California, this is the code your compliance report runs against.

Most of what you have heard about it is either exaggerated or about nonresidential buildings. Here is the residential picture.

Heat pumps became the baseline

This is the change with the most money attached to it.

There are two ways to comply, and the answer is different on each.

On the prescriptive path, the checklist route, §150.1(c) now requires the heating equipment to be a heat pump, in all sixteen climate zones. Not a preference, a requirement. If you want a gas furnace, the prescriptive path is closed to you.

On the performance path, the modelled route, the code sets a standard design your building has to match or beat, and that standard design assumes a heat pump. Here you are not required to install one. You are required to be as efficient as a building that did.

That distinction is where the money is. Put a gas furnace in a house whose standard design assumed a heat pump and you now have a gap to close somewhere else: better windows, more insulation, tighter ducts, a bigger solar array. Sometimes closing that gap is cheap. Sometimes it costs more than the heat pump would have.

This is worth a phone call before the mechanical plans are finished, not after.

Water heating moved the same way. Gas tankless water heaters were removed from the prescriptive options for single-family additions, and the old exception for gas tankless in Climate Zones 3, 4, 13 and 14 has gone.

How compliance is measured changed too

Under the 2022 code, the performance path measured your energy budget in TDV, time dependent valuation. The 2025 code replaces it with LSC, long-term system cost, alongside source energy.

This is invisible on a drawing and it matters anyway: it changes which trade-offs the model rewards. A measure that bought you margin under TDV does not necessarily buy the same margin under LSC. If you are used to what worked on 2022 projects, expect the model to disagree with you occasionally.

Solar and battery storage

New homes have carried a solar PV requirement since the 2019 code. The 2025 code keeps it, changes how the array is sized, and adds a battery requirement of a different kind.

PV sizing is now based on total solar access roof area: that area multiplied by 18 for steep-sloped roofs, or by 14 for low-sloped ones.

Battery storage is now a readiness requirement rather than an install requirement. A newly built one or two dwelling unit home with electrical service over 125A has to be battery-ready. Fit an actual battery and the readiness requirement falls away.

Two things people get wrong here:

• Additions and remodels are not caught by it. The PV requirement lands on newly constructed dwellings, not on adding a bedroom to an existing house.
• An attached ADU is treated as an addition, so the PV requirement does not reach it.
• Many detached ADUs fall out of it too, but not because of a size rule written into the code. The array is sized by formula, and where the formula produces a system below the minimum it is waived. In practice that takes a lot of small detached ADUs out of it, with the cut-off depending on the climate zone and the roof. There is also an exemption where shading leaves too little usable roof.
• The other rules still apply in full. Envelope, HVAC and water heating do not care whether the PV requirement was waived, and that is what catches people out.

Do not take the ADU position on trust for a specific project. It turns on the sizing calculation for that roof in that climate zone, which is a five-minute job to check and an expensive thing to assume.

What did not change

Quite a lot, and this is the part nobody writes about.

The envelope rules are recognisably the same. Insulation, window U-factor and SHGC, air sealing, duct sealing, and quality insulation installation all work the way they did under the 2022 code. Climate zone still drives the design assumptions. The forms are still CF1R for residential, still registered the same way, still field-verified by an independent rater.

If you built under the 2022 code, you are not starting from scratch. You are adjusting.

Where projects actually get into trouble

Not in the code text. In three practical places.

The permit application date. The 2025 code follows the date the application was submitted, not when the drawings were done or when construction starts. A project filed in late 2025 stays on the 2022 code. If that application lapses and gets refiled, it moves to 2025 and the requirements change underneath it. There is a code cycle checker on this site if you want to check yours.

Glazing area on the prescriptive path. Large windows are the most common reason a project cannot use the prescriptive checklist and has to be modelled on the performance path instead. That is not a failure, just a different route, and usually the cheaper one for a modern design. Our glazing checker screens it in about ten seconds.

Value engineering after the model is done. Someone takes out the measure the compliance model took credit for, nobody tells the energy consultant, and it surfaces at field verification. This is the single most expensive mistake in residential compliance, and it is entirely avoidable with one email.

What this means for your project

If your permit application goes in during 2026, you are on the 2025 code and the mechanical decision is the one worth thinking about early. Model it before the equipment is ordered and you get to choose the cheapest compliant path. Model it afterwards and you are closing a gap the hard way.

An ADU or JADU on the prescriptive path is $200 and comes back in two business days. Additions and remodels start at $300, new homes at $300. The calculator gives you the number without you contacting anyone first.