For code officials and people like specifiers, the language of codes is familiar and comfortable. For the rest of us, it can seem a bit overwhelming, so we put together an overview of some of the basic codes and test requirements you might encounter regarding the weatherization of residential and light commercial structures.
Where do codes come from?
Multiple organizations have a say in building codes. The International Code Council (ICC) creates both the International Building Code (IBC) and the International Residential Code (IRC). The IRC refers to requirements for detached one- and two-family dwellings and townhouses not more than three stories above grade, while the IBC applies to structures not covered by the IRC. States and local authorities may adopt these codes as created or add their own specific requirements to them.
The IBC and IRC are updated every three years; however, the active code in many states is several years behind the most recent issue. The IBC and the IRC dictate what materials meet the requirements for weatherization purposes. In some cases, the building codes identify a single material as allowed but may provide for approved alternate materials as well. The ICC creates Acceptance Criteria that define the testing methods and performance requirements for approval of alternate material under the building code. Acceptance criteria of note for weatherization materials include:
- ICC AC-38 for Water-Resistive Barriers
- ICC AC-148 for Flashing Materials
- ICC AC-356 Drainage Systems for Plaster or Masonry Veneer
Other trade and standards organizations also have a direct influence on the weatherization materials allowed by the building codes. ASTM International (American Society for Testing and Materials) and the American Architectural Manufacturers Association (AAMA), for example, provide standards and material specifications referenced in the building code for allowed products.
Chapter 14 Exterior Walls
1402.2 Weather protection. Exterior walls shall provide the building with a weather-resistant exterior wall envelope. The exterior wall envelope shall include flashing, as described in Section 1404.4. The exterior wall envelope shall be designed and constructed in such a manner as to prevent the accumulation of water within the wall assembly by providing a water-resistive barrier behind the exterior veneer, as described in Section 1403.2, and a means for draining water that enters the assembly to the exterior. Protection against condensation in the exterior wall assembly shall be provided in accordance with Section 1404.3.
1403.5 Vertical and lateral flame propagation. Exterior walls on buildings of Type I, II, III or IV construction that are greater than 40 feet (12 192mm) in height above grade plane and contain a combustible water-resistive barrier shall be tested in accordance with and comply with the acceptance criteria of NFPA 285. For the purposes of this section, fenestration products, flashing of fenestration products and weather-resistive barrier flashing and accessories at other locations, including through wall flashing, shall not be considered part of the water-resistive barrier.
- Walls in which the water-resistive barrier is the only combustible component and the exterior wall has a wall covering of brick, concrete, stone, terra cotta, stucco or steel with minimum thicknesses in accordance with Table 1404.2.
Walls in which the water-resistive barrier is the only combustible component and the water-resistive barrier has a peak heat release rate of less than 150 kW/m2, a total heat release of less than 20 MJ/m2 and an effective heat of combustion of less than 18 MJ/kg as determined in accordance with ASTM E 1354 and has a flame spread index of 25 or less and a smoke-developed index of 450 or less as determined in accordance with ASTM E 84 or UL 723. The ASTM E 1354 test shall be conducted on specimens at the thickness intended for use, in the horizontal orientation and at an incident radiant heat flux of 50 kW/m2.
1403.2 Water-resistive barrier. Not fewer than one layer of No. 15 asphalt felt, complying with ASTM D226 for Type I felt or other approved materials, shall be attached to the studs or sheathing, with flashing as described in Section 1404.4, in such a manner as to provide a continuous water-resistive barrier behind the exterior wall veneer.
1404.4 Flashing. Flashing shall be installed in such a manner so as to prevent moisture from entering the wall or to redirect that moisture to the exterior. Flashing shall be installed at the perimeters of exterior door and window assemblies, penetrations and terminations of exterior wall assemblies, exterior wall intersections with roofs, chimneys, porches.
Chapter 25 Gypsum Board, Gypsum Panel Products, and Plaster
For Cement Plaster/Stucco
2510.6 Water-resistive barriers. Water-resistive barriers shall be installed as required in Section 1403.2 and, where applied over wood-based sheathing, shall include a water-resistive vapor-permeable barrier with a performance at least equivalent to two layers of water-resistive barrier complying with ASTM E2556, Type I. The individual layers shall be installed independently such that each layer provides a separate continuous plane and any flashing (installed in accordance with Section 1404.4) intended to drain to the water-resistive barrier is directed between the layers.
- Where the water-resistive barrier that is applied over wood-based sheathing has a water resistance equal to or greater than that of a water-resistive barrier complying with ASTM E2556, Type II and is separated from the stucco by an intervening, substantially non-water-absorbing layer or drainage space.
- Where the water-resistive barrier is applied over wood-based sheathing in Climate Zone 1A, 2A, or 3A, a ventilated air space shall be provided between the stucco and the water-resistive barrier.
The 2018 IRC
Chapter 7 Wall Covering
R703.1 General. Exterior walls shall provide the building with a weather-resistant exterior wall envelope. The exterior wall envelope shall include flashing as described in Section R703.4.
R703.1.1 Water resistance. The exterior wall envelope shall be designed and constructed in a manner that prevents the accumulation of water within the wall assembly by providing a water-resistant barrier behind the exterior veneer as required by Section R703.2 and a means of draining to the exterior water that enters the assembly.
Importance of Moisture Management
R703.2 Water-resistive barrier. One layer of No. 15 asphalt felt, free from holes and breaks, complying with ASTM D226 for Type I felt or other approved water-resistive barrier shall be applied over studs or sheathing of all exterior walls. Such felt or material shall be applied horizontally, with the upper layer lapped over the lower layer not less than 2 inches (51mm). Where joints occur, felt shall be lapped not less than 6 inches (152mm). The felt or other approved material shall be continuous to the top of walls and terminated at penetrations and building appendages in a manner to meet the requirements of the exterior wall envelope as described in Section R703.1.
R703.4 Flashing. Approved corrosion-resistant flashing shall be applied shingle-fashion in a manner to prevent the entry of water into the wall cavity or penetration of water to the building structural framing components. Self-adhered membranes used as flashing shall comply with AAMA (Ameri-can Architectural Manufacturers Association) 711. Fluid-applied membranes used as flashing in exterior walls shall comply with AAMA 714. The flashing shall extend to the surface of the exterior wall finish. Approved corrosion-resistant flashings shall be installed at:
- Exterior window and door openings. Flashing at exterior window and door openings shall extend to the surface of the exterior wall finish or to the water-resistive barrier complying with Section R703.2 for subsequent drainage. Mechanically attached flexible flashings shall comply with AAMA 712.
R703.7.3 Water-resistive barriers. Water-resistive barriers shall be installed as required in Section R703.2 and, where applied over wood-based sheathing, shall include a water-resistive vapor-permeable barrier with a performance at least equivalent to two layers of Grade D paper. The individual layers shall be installed independently such that each layer provides a separate continuous plane and any flashing (installed in accordance with Section R703.4) intended to drain to the water-resistive barrier is directed between the layers.
- Where the water-resistive barrier that is applied over wood-based sheathing has a water resistance equal to or greater than that of 60-minute Grade D paper and is separated from the stucco by an intervening, substantially non-water-absorbing layer or designed drainage space.
Additional energy code requirements may dictate the exterior envelope including an air barrier. These requirements will vary based on jurisdiction, including different requirements from county to county, so check with the local building department.
These are the primary weatherization codes you’ll encounter in residential and light commercial construction. Beyond them, you may encounter references to test methods for specific performance criteria or physical properties of materials. Typically, these tests will validate compliance with some aspect of the code and are not separate or additional to the code. So, while you may not be a code geek, we hope you feel a little more confident in your understanding of weatherization building codes. Remember, understanding codes, guidelines, and best practices is all part of ensuring that you can build at the highest quality and avoid issues.
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Contact a Henry weatherization expert for advice and support on your next job.