Insulation and Title 24

Roof/Ceiling Insulation


Insulation in roof/ceiling constructions must be placed in direct contact with the infiltration barrier. In most cases the attic is ventilated and the infiltration barrier is the drywall ceiling; in this case, the insulation must lie directly on top of the ceiling.


Ceiling insulation should extend far enough to the outside walls to cover the bottom chord of the truss. However, insulation should not block eave vents in attics because if the flow of air is blocked, moisture may build up in the attic and water vapor may condense on the underside of the roof. This can cause structural damage and reduce the insulation’s effectiveness. Insulation may be tapered near the eave, but it must be applied at a rate to cover the entire ceiling at the specified level.


Loose fill insulation must be blown in evenly, and insulation levels can be verified by checking that the depth of insulation conforms to the manufacturer’s coverage chart for achieving the required R-value. The insulation must also meet the manufacturer’s specified minimum weight per sq.ft. for the corresponding R-value.

Wall Insulation

Batt insulation should fill the wall cavity evenly. If Kraft or foil-faced insulation is used, it should be installed per manufacturer recommendations to minimize air leakage and avoid sagging of the insulation. Wall insulation should extend into the perimeter floor joist (rim joist) cavities along the same plane as the wall. If a vapor barrier is required, it must be installed on the conditioned space side of the framing. Because it is difficult to inspect wall insulation behind tub/shower enclosures after the enclosures are installed, insulation of these wall sections should be inspected during the framing inspection. 

Floor Insulation


Floor insulation should be installed in direct contact with the subfloor so that there is no air space between the insulation and the floor. Support is needed to prevent the insulation from falling, sagging, or deteriorating. Options for support include netting stapled to the underside of floor joists, insulation hangers running perpendicular to the joists, or other suitable means. Insulation hangers should be spaced at 18 inch or less prior to rolling out the insulation. Insulation hangers are heavy wires up to 48 inches long with pointed ends, which provide positive wood penetration. Netting or mesh should be nailed or stapled to the underside of the joists. Floor insulation should not cover foundation vents.


Slab Insulation


The Title 24 mandatory measures do not require unheated slab insulation, but when the prescriptive requirements call for it (zone 16), the mandatory measures require that the insulation material must be suitable for the application and meet the requirements. An example of an insulating material that meets the requirements is smooth-skin extruded polystyrene.


Slab insulation must be protected from physical and UV degradation by either installing a water-resistant protection board, extending sheet metal flashing below grade, choosing an insulation product that has a hard durable surface on one side, or by other suitable means. Slab edge insulation is mandatory with heated slabs, as required by the Title 24 energy standards. See the Title 24 residential compliance manual for details.


(Excerpted from the Title 24 Residential Compliance Manual)