Washington Administrative Code › Title 51 - Enterprise Services, Department of (Building Code Council) › Chapter 51-11R - State Building Code adoption and amendment of the 2021 edition of the International Energy Conservation Code, Residential › Section 51-11R-40320 - Section R403.3-Ducts

Current through Register Vol. 24-14, July 15, 2024
R403.3
Ducts.
Ducts and air handlers shall be installed in accordance
			 with Sections R403.3.1 through R403.3.7.
R403.3.1
Ducts located outside
			 conditioned space.
Supply and return ducts located outside
conditioned space
shall be insulated to an
R
-value of not less than R-8 for ducts 3 inches (76 mm) in
			 diameter and larger and not less than R-6 for ducts smaller than 3 inches (76
			 mm) in diameter. Ducts buried beneath a building shall be insulated as required
			 per this section or have an equivalent thermal distribution efficiency. Ducts
			 within a concrete slab or in the ground shall be insulated to R-10 with
			 insulation designed to be used below grade. Underground ducts utilizing the
thermal distribution efficiency
method shall be listed and
			 labeled to indicate the R-value equivalency.
R403.3.2
Ducts located in conditioned
			 space.
For ducts to be considered as being located inside a conditioned
			 space, such ducts shall comply with the following:
1. All duct systems shall be located
			 completely within the
continuous air barrier
and within the
building thermal envelope
.
2. All heating, cooling, and ventilation
			 system components shall be installed inside the conditioned space including,
			 but not limited to, forced air ducts, hydronic piping, hydronic floor heating
			 loops, convectors and radiators. Combustion equipment shall be direct vent or
			 sealed combustion.
3. For forced
			 air ducts, a maximum of 10 linear feet of return ducts and 5 linear feet of
			 supply ducts is permitted to be located outside the conditioned space, provided
			 they are insulated to a minimum of R-8.
3.1.
			 Metallic ducts located outside the conditioned space must have both transverse
			 and longitudinal joints sealed with mastic.
3.2. If flex ducts are used, they cannot
			 contain splices. Flex duct connections must be made with nylon straps and
			 installed using a plastic strapping tensioning tool.
4. Ductwork in floor cavities located over
			 unconditioned space shall comply with all of the following:
4.1. A
continuous air
			 barrier
installed between unconditioned space and the duct.
4.2. Insulation installed in accordance with
			 Section R402.2.7.
4.3. A minimum
			 R-19 insulation installed in the cavity width separating the duct from
			 unconditioned space.
5.
			 Ductwork located within
exterior walls
of the
building
			 thermal envelope
shall comply with the following:
5.1. A continuous air barrier installed
			 between unconditioned space and the duct.
5.2. A minimum R-10 insulation installed in
			 the cavity width separating the duct from unconditioned space.
5.3. The remainder of the cavity insulation
			 shall be fully insulated to the drywall side.
R403.3.3
Ducts buried within ceiling
			 insulation.
Where supply and return air ducts are partially or
			 completely buried in ceiling insulation, such ducts shall comply with all of
			 the following:
1. The supply and return ducts
			 shall have an insulation
R
-value not less than R-8.
2. At all points along each duct, the sum of
			 the ceiling insulation
R
-value against and above the top of
			 the duct, and against and below the bottom of the duct, shall be not less than
			 R-19, excluding the
R
-value of the duct insulation.
EXCEPTION:
Sections of the supply duct that are less than 3 feet
						  (914 mm) from the supply outlet shall not be required to comply with these
						  requirements.
R403.3.3.1
Effective
R
-value of deeply buried ducts.
Where using the total
			 building performance compliance option in Section R405, sections of ducts that
			 are: Installed in accordance with Section R403.3.3; located directly on, or
			 within 5.5 inches (140 mm) of the ceiling; surrounded with blown-in attic
			 insulation having an
R
-value of R-30 or greater and located
			 such that the top of the duct is not less than 3.5 inches (89 mm) below the top
			 of the insulation, shall be considered as having an effective duct insulation
R
-value of R-25.
R403.3.4
Sealing.
Ducts, air
			 handlers, and filter boxes shall be sealed. Joints and seams shall comply with
			 either the
International Mechanical Code
or
International Residential Code
, as applicable.
EXCEPTIONS:
1. Air-impermeable spray foam products shall be
						  permitted to be applied without additional joint seals.
2. For ducts having a static pressure classification of
						  less than 2 inches of water column (500 Pa), additional closure systems shall
						  not be required for continuously welded joints and seams, and locking-type
						  joints and seams of other than the snap-lock and button-lock types.
R403.3.4.1
Sealed air handler.
Air handlers shall have a manufacturer's designation
			 for an air leakage of no more than 2 percent of the design air flow rate when
			 tested in accordance with ASHRAE 193.
R403.3.5
Duct testing.
Ducts
			 shall be leak tested in accordance with WSU RS-33, using the maximum duct
			 leakage rates specified.
EXCEPTION:
A duct air leakage test shall not be required for ducts
						  serving ventilation systems that are not integrated with the ducts serving
						  heating or cooling systems.
A written report of the results shall be signed by the party
				conducting the test and provided to the
code official
.
R403.3.6
Duct
			 leakage.
The total leakage of the ducts, where measured in accordance
			 with Section R403.3.3, shall be as follows:
1.
			 Rough-in test: Total leakage shall be less than or equal to 4.0 cfm (113.3
			 L/min) per 100 square feet (9.29 m2) of conditioned
			 floor area when tested at a pressure differential of 0.1 inches w.g. (25 Pa)
			 across the system, including the manufacturer's air handler enclosure. All
			 registers shall be taped or otherwise sealed during the test. If the air
			 handler is not installed at the time of the test, total leakage shall be less
			 than or equal to 3.0 cfm (85 L/min) per 100 square feet (9.29
			 m2) of conditioned floor area.
2. Postconstruction test: Leakage to outdoors
			 shall be less than or equal to 4.0 cfm (113.3 L/min) per 100 square feet (9.29
			 m2) of conditioned floor area or total leakage shall
			 be less than or equal to 4.0 cfm (113.3 L/min) per 100 square feet (9.29
			 m2) of conditioned floor area when tested at a
			 pressure differential of 0.1 inches w.g. (25 Pa) across the entire system,
			 including the manufacturer's air handler enclosure. All register boots shall be
			 taped or otherwise sealed during the test.
3. Test for ducts within thermal envelope:
			 Where all ducts and air handlers are located entirely within the
building thermal envelope
, total leakage shall be less than or
			 equal to 8.0 cubic feet per minute (226.6 L/min) per 100 square feet (9.29
			 m2) of conditioned floor area. For forced air ducts,
			 a maximum of 10 linear feet of return ducts and 5 linear feet of supply ducts
			 may be located outside the conditioned space. All metallic ducts located
			 outside the conditioned space must have both transverse and longitudinal joints
			 sealed with mastic. If flex ducts are used, they cannot contain splices. Flex
			 duct connections must be made with nylon straps and installed using a plastic
			 strapping tensioning tool. Ducts located in crawl spaces do not qualify for
			 this exception.
R403.3.7
Building cavities.
Building framing cavities shall not be used as
			 ducts or plenums. Installation of ducts in exterior walls, floors or ceilings
			 shall not displace required envelope insulation.