Title 24 insulation
Insulation is one of the least expensive measures to improve building energy efficiency.
Insulation requires no maintenance, helps improve indoor comfort, and provides excellent
sound control. Adding extra insulation at a later time is much more expensive than
maximizing insulation levels at the beginning of construction.
Type of Insulation
There are four basic types of insulation, or insulation “systems,” installed in residential
buildings and the use vary based on the design and type of construction:
- Batt and Blanket: Batt and blanket insulation is made of mineral fiber and mineral wool
– either processed fiberglass, rock, or slag wool; natural wool products—animal wool or
cotton-based products; or cellulose materials. These products are used to insulate
below floors, above ceilings, below roofs, and within walls. They offer ease of
installation with R-values set by the manufacturer based on size and thickness.
Batt and blanket insulation allow easy inspection, and installation errors can readily be
identified and remedied, including breeches in the air barrier system that allow air
- Loose-Fill Insulation: There are several commonly used types of insulation that have
a blown installation process, including cellulose, fiberglass, and natural
wool (animal- or cotton-based products). Blown wall insulation can be an effective way
to deal with the irregularities of wall cavities, especially the spaces around pipes,
electric cables, junction boxes, and other equipment that is embedded in cavities. The R-value of blown wall insulation material installed in closed cavities
is determined by the installed thickness. This differs from manufactured products such
as fiberglass or mineral wool batts for which the R-value has been tested and arrives at
the construction site in preformed lengths and thicknesses with set R-value
When installed in floors, walls, and other vertical assemblies, these fibrous insulations
are held in place in one of three ways:
1. Pre-installed netting or fabric
2. Use of existing cavity walls
3. Use of integral adhesives
- Spray Polyurethane Foam (SPF): SPF is a two-part, liquid-foamed thermoset plastic
(such as polyurethane). Polyurethane is formed by the reaction of an isocyanate and a
polyol. Blowing agents, catalysts, and surfactants are added to develop a cellular
structure before the polyurethane mixtures cures. When this mixture is applied to
substrate materials, the SPF material forms in place to provide insulation, an air seal,
and, in the case of closed-cell SPF, an integral vapor retarder and water barrier.
SPF insulation is a two-component reactive system mixed at a spray gun or a singlecomponent system that cures by exposure to humidity. The liquid is sprayed through a
nozzle into the wall, roof/ceiling, and floor cavities. SPF insulation can be formulated to
have specific physical properties (such as density, compressive strength, fire resistance,
SPF insulation is spray-applied to adhere fully to the joist and other framing faces to
form a complete air seal within the construction cavities.
There are two types of SPF insulation:
a. Low-Density Open-Cell SPF (ocSPF) Insulation: A spray-applied polyurethane
foam insulation having an open cellular structure resulting in an installed nominal
density of 0.4 to 1.5 pounds per cubic foot (pcf), ocSPF has been assigned a default
R-value of 3.6 per inch for compliance purposes, but some products can achieve
higher R-values. The ocSPF insulation is sprayed then expands to fill the framed
cavity. Excess insulation is removed with a special tool. Theaverage thickness of the foam insulation must meet or exceed the required R-value.
- Medium-Density Closed-Cell SPF (ccSPF) Insulation: A spray-applied
polyurethane foam insulation having a closed cellular structure resulting in an installed
nominal density of greater than 1.5 to less than 2.5 pounds per cubic foot (pcf), ccSPF
has been assigned a default R-value of 5.8 per inch for compliance, but some products
can achieve higher R-values. The average thickness of the foam insulation must meet
or exceed the required R-value.
Required Thickness of SPF Insulation to Archive Default R-Values
Rigid Insulation: Rigid board insulation sheathing is made from fiberglass, expanded
polystyrene (EPS), extruded polystyrene (XPS), polyisocyanurate (ISO), or
polyurethane. It varies in thickness, and some products can provide up to R-6 per inch of
This type of insulation is used for above-roof decks, exterior walls, cathedral ceilings,
basement walls, as perimeter insulation at concrete slab edges, and to insulate special
framing situations such as window and door headers, and around metal seismic bracing.
Rigid board insulation may also be integral to exterior siding materials. Properly sealed
rigid insulation can be used continuously across an envelope surface to reduce air
infiltration and exfiltration, and thermal bridging at framing.
- Title 24 prescribes 3 paths for insulating roofs in order to comply with the standard. Any one of these options can be applied.
- Above-Roof Rafter Insulation (Option A):
In a vented attic, rigid board insulation can be installed above the roof rafters to add
value to the thermal integrity of the roof system.
Above-rafter insulation can be implemented with either asphalt shingles or clay/concrete
tiles.Whenabove-rafter insulation is installed, a radiant barrier must also be installed in the requiredclimate zones.
- Below-Deck Insulation (Option B):
In a vented attic, air-permeable or air-impermeable insulation (that is, batt, spray foam,
loose-fill cellulose, or fiberglass) should be placed directly below the roof deck between
the truss members and secured in place to provide a thermal barrier for the attic space.
Insulation must be indirect contact with the roof deck and secured by the insulation adhesion, facing,mechanical fasteners, wire systems, a membrane material, or netting.
Proper attic ventilation must always be maintained to prevent the potential for moisture
Roof Insulation Option A (Left) and Option B (Right)
- Duct and Air Handlers Located in Conditioned Space (Option C):
Option C allows a project to place and verify that ducts are located in conditioned space
instead of installing insulation at the roof deck. In this case insulation is installed at the ceiling level. Radiant barrier is also required in some climate zones. Simply locating ducts inconditioned space does not qualify for this requirement; a HERS Rater must test andverify the system and that the ducts are insulated to a required level.
- Raised Heel or Extension Truss (Energy Truss)
The use of an energy truss, usually referred to as a raised heel or extension truss, allows
full depth, uncompressed insulation at the ceiling to continue to the ceiling edge where the
roof and ceiling meet. For this strategy, the roof truss is assembled with an additional
vertical wood framed section at the point where the top and bottom truss chords meet. The
vertical section raises the top chord and provides increased space that can be filled with
Benefits of this strategyinclude:
- Realizing the full benefit of ceiling insulation.
• Providing more space for air handler and duct systems if located in the attic
Raised Heel or Extension Truss (Energy Truss)
Slab / Raised Floor Insulation
- Raised Floor often occurs in a building where there is a crawlspace or when upper floor extends beyond the walls of the lower floor. Title 24 requires these conditions to be properly insulated.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 before rolling out the insulation. Insulation hangers are heavy wires up to 48 inch 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.
Raised Floor Insulation
Raised slab floors with radiant heat (heated slab floors) must meet special insulation
When a controlled ventilated or an unvented crawlspace is used, raised-floor insulation isnot required, although vapor retarder is required over the ground, and the foundation wallsmust be insulated
Slab Insulation requirement changes by climate zone. The reason for this is that ground temperature varies between climate zones resulting in varying energy loss through the slab. Title 24 provides a number of options in term of slab insulation location.
Allowed Slab Edge Insulation Placement
The 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 Insulation Requirements for Heated Slab Floors
(Excerpted from CEC Title-24 Part 6 Residential Compliance Manual)