Is an unheated attic storage room regulated?

If it is neither heated, cooled nor indirectly conditioned, it stays unconditioned space and only its lighting is regulated. Adding heating, cooling or a permanent open connection to the house can make it conditioned space.

What R-value do I need in the rafters of an attic conversion?

For a conversion of 700 square feet or less, R-22 between wood framing or an assembly U-factor of 0.043, under §150.0(a). Above 700 square feet the prescriptive cathedral ceiling value is R-38.

Do knee walls need insulation?

Yes. The compliance manual says knee walls meet the mandatory wall insulation of §150.0(c): R-15 in 2x4 framing or R-21 in 2x6.

Is a loft in a vaulted ceiling the same as an attic conversion?

No. A loft inside existing conditioned volume adds floor area but not volume, so the compliance manual treats it as an alteration rather than an addition.

Does an Attic Conversion Need Title 24?

Yes: turning an unconditioned attic into a heated or cooled room is newly conditioned space, which §100.1 says must comply as an addition. The insulation moves to the roof line and the knee walls, with at least R-22 in an enclosed rafter ceiling for a conversion of 700 square feet or less, the mandatory wall values in knee walls, and dormer glazing counted against the addition’s caps.

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Why a conversion is an addition, not a remodel

An attic sits outside the conditioned envelope, with the insulation on the ceiling below it. Converting it adds conditioned floor area and conditioned volume, which is the §100.1 definition of an addition, and the definition of newly conditioned space says such space must comply with the requirements for an addition. The compliance manual draws the contrast with a loft built inside an existing vaulted room: that adds floor area but no conditioned volume, so it is an alteration.

Where the insulation goes

Once the room is conditioned, the thermal boundary moves from the old attic floor to the roof and the side walls of the new room.

Sloped ceilings in the rafters. For a conversion of 700 square feet or less, the exception to §150.2(a)1B sends an enclosed rafter ceiling back to §150.0: R-22 between wood framing, or an assembly U-factor of 0.043. Over 700 square feet the prescriptive package applies, and its cathedral ceiling option calls for R-38 in every zone.
Flat ceilings with attic above. A ventilated attic left over the new room, such as the space above collar ties, takes the addition values: R-38 in zones 1, 2, 4 and 8 to 16, R-30 in zones 3 and 5 to 7, and a radiant barrier in zones 2 to 15 for conversions of 700 square feet or less.
Knee walls. The short walls between the new room and the attic behind them separate conditioned from unconditioned space. The manual says knee walls meet the mandatory wall insulation of §150.0(c), R-15 in 2x4 framing or R-21 in 2x6, rather than the prescriptive wall values.
Access hatches. Doors into the leftover attic need permanently attached insulation and a gasket under §150.0(a)3.

The R-22 figure is a mandatory floor that no compliance path trades below, but it is an assembly value: the manual notes that rigid insulation not penetrated by framing can have a rated R-value under R-22, so long as the roof assembly reaches U-0.043. That helps where rafters are shallow.

Dormers and roof windows

New dormer windows and skylights are glazing in the addition. For a conversion of 400 square feet or less, total fenestration is capped at 75 square feet or 30 per cent of the floor area, whichever is greater, and in zones 2, 4 and 6 to 15 west-facing glazing is held to 60 square feet. The products meet the Table 150.1-A U-factor and SHGC; skylight specifics are on Title 24 skylight requirements.

Heating, ventilation and lighting

Extending the existing ducts into the new room brings the whole existing duct system under the sealing and testing rules of §150.2(b)1D (Exception 4 to §150.2(a)). The existing equipment need not meet Part 6 itself, but must still have the heating capacity CRC 303.10 requires. A ductless system avoids the duct test. Conversions of 1,000 square feet or less are excused from the whole-dwelling ventilation airflow, but a new bathroom needs local exhaust under §150.0(o)1G, and new lighting meets §150.0(k).

Relief for existing framing

QII applies only to conversions over 700 square feet, and even then §150.2(a)1Av relieves conversions of unconditioned space of two items: existing window and door headers need not be insulated, and air sealing is not required where the existing air barrier is not removed or replaced. The general rules for adding space are on does a room addition need Title 24.