Install an air barrier behind staircases installed on exterior walls.
- Install insulation without misalignments, compressions, gaps, or voids in exterior wall cavities behind staircases installed along exterior walls.
- Install a rigid air barrier to prevent wall cavity insulation from sagging and to create a continuous thermal barrier. Rigid air barrier material could include rigid foam insulation, drywall, plywood, or OSB, among others.
- Seal all seams, gaps, and holes in the air barrier with caulk or foam.
- Ensure that the air barrier is continuous and in full contact with the insulation.
- If spray foam insulation is used for the wall cavity insulation, the spray foam can serve as the air barrier if it is at least 5.5 inches thick if open-cell or at least 1.5 inches thick if closed-cell spray foam insulation.
- ENERGY STAR requires that an air barrier be installed at the exterior vertical surface of the wall insulation in all climate zones and also that an air barrier be installed at the interior vertical surface in IECC Climate Zones 4-8 (ENERGY STAR 2015).
See the Compliance Tab for related codes and standards, and criteria to meet national programs such as ENERGY STAR Certified Homes, DOE’s Zero Energy Ready Home program, and EPA’s Indoor airPLUS.
Staircases and staircase landings are often located along exterior walls or walls adjoining unconditioned spaces like garages or attics. Insulating and air blocking of the exterior wall below the stairs is sometimes overlooked. When the insulation in the exterior wall cavities is not fully aligned with (touching) the interior wall sheathing (drywall), the insulation’s effectiveness is reduced. After filling the wall cavities with insulation, the walls should be covered with a rigid air barrier material such as rigid foam insulation, OSB, or drywall that is taped at any seams and sealed to the bottom plate, top plate, and framing at the edges with caulk. The insulation should fill the cavity and be fully aligned with the rigid sheathing.
Staircases may be prefabricated or custom site-built. Prefabricated stairs are often used when the stairs will be covered with carpet, although they can be ordered with hardwood and custom finishes. Custom staircases are sometimes built when the stair treads will be hardwood.
Prefabricated stairs come with the stair treads and risers already attached to the stringer boards. The most common varieties are the notched stringer stair and the routed stringer stair. The notched staircase uses three stringers that are cut out or notched to hold the stair step treads and risers. Routed stringer stairs use two stringer boards that are not notched. The routed stringer differs from the notched stair by utilizing two visible skirt boards as its structural support stringers. Each stringer is usually a solid finished piece of wood, typically 12 inches high and 1.25 inches thick, that is routed to hold the treads and risers. The steps are nailed and glued to the stringers. Because these stringer boards extend above and below the sides of the steps, they serve as the finish boards as well.
These materials may be installed by insulators, framers, or drywallers. This task should be included in the contract for the appropriate trade depending on the workflow at the specific job site.
How to Install a Prefabricated Routed Stringer Staircase
- If a prefabricated routed stringer staircase is used, insulate the wall, then attach the bottom end of the stringers to the floor and the top end to the second floor or landing. Fasten the staircase through the stringer boards to the exterior wall studs. Install drywall cut at a diagonal to fit from the top of the stringer/finish board to the ceiling. Apply caulk or joint compound to the seam between the top of the finish board and the drywall. Cover the seam with trim.
- Below the stairs, apply caulk to the exterior wall framing and to the bottom edge of the stringer board, then install rigid foam, drywall, or another sheet good from the bottom of the stringer/finish board to the bottom plate of the wall. Caulk or tape any seams.
How to Install a Site-Built or Prefabricated Notched Stringer Staircase on an Exterior Wall
- Attach a spacer board to the outer side of the outside notched stringer boards. Attach the spacer board flush with the bottom edge of the stringer board. The spacer board should be thick enough to allow room to slide the drywall between the stringer and the exterior wall studs. If you want to install a finish board along the steps, use a wider spacer (e.g., a 2x4) that will accommodate the thickness of both the drywall and the finish board.
- Attach the stringers at the base floor and the second floor or landing. Insulate the wall. Attach the stringer board to the exterior wall studs through the spacer board. The spacer board will give you room to slide the drywall between the riser and the exterior wall studs.
3. Cut drywall to fit from the top of the spacer board to the ceiling. Apply caulk or joint compound along the top of the spacer (or bottom edge of the drywall). Slide the drywall behind the stringer board so it is resting on the spacer board and fasten it to the exterior wall studs. Install a finish board next to the drywall if desired.
4. Below the stairs, apply caulk to the exterior wall framing and the bottom edge of the spacer board then install rigid foam, drywall, or another sheet good from the bottom of the stringer board to the bottom plate of the wall. Caulk or tape any seams.
The site supervisor should visually inspect the exterior wall underneath staircases or staircase landings located on exterior walls during construction to confirm that the wall cavity is insulated and that a rigid air barrier material is installed on the interior surface of the exterior wall in contact with the cavity insulation. Blower door testing conducted as part of whole-house energy performance testing may help indicate if there are air leaks at staircases. High-performance branding programs and the 2009 and 2012 IECC require that builders meet specified insulation levels and infiltration rates. See the “compliance” tab for these specified infiltration rates.
Thermal Enclosure Checklist, Fully-Aligned Air Barriers. A complete air barrier that is fully aligned with insulation is to be provided at exterior surface of walls in all climate zones and at interior surface of walls for Climate Zones 4-8. All insulated vertical surfaces are considered walls (e.g., above and below grade exterior walls, knee walls) and must meet the air barrier requirements for walls, with the exception of adiabatic walls in multifamily dwellings.
Exhibit 2: DOE Zero Energy Ready Home Target Home. Infiltration (ACH50): Zones 1-2: 3; Zones 3-4: 2.5; Zones 5-7: 2; Zone 8: 1.5. Envelope leakage shall be determined by an approved verifier using a RESNET-approved testing protocol.
International Energy Conservation Code (IECC) Climate Regions
ENERGY STAR Certified Homes (Version 3/3.1, Revision 08), Rater Field Checklist
Thermal Enclosure System:
2. Fully-Aligned Air Barriers.5 At each insulated location below, a complete air barrier is provided that is fully aligned as follows:
Walls: At exterior vertical surface of wall insulation in all climate zones; also at interior vertical surface of wall insulation in Climate Zones 4-8.7
2.2 Walls behind showers, tubs, staircases, and fireplaces.
(5) For purposes of this Checklist, an air barrier is defined as any durable solid material that blocks air flow between conditioned space and unconditioned space, including necessary sealing to block excessive air flow at edges and seams and adequate support to resist positive and negative pressures without displacement or damage. EPA recommends, but does not require, rigid air barriers. Open-cell or closed-cell foam shall have a finished thickness ≥ 5.5 in. or 1.5 in., respectively, to qualify as an air barrier unless the manufacturer indicates otherwise. If flexible air barriers such as house wrap are used, they shall be fully sealed at all seams and edges and supported using fasteners with caps or heads ≥ 1 in. diameter unless otherwise indicated by the manufacturer. Flexible air barriers shall not be made of kraft paper, paper-based products, or other materials that are easily torn. If polyethylene is used, its thickness shall be ≥ 6 mil.
(7) All insulated vertical surfaces are considered walls (e.g., above and below grade exterior walls, knee walls) and must meet the air barrier requirements for walls. The following exceptions apply: air barriers recommended, but not required, in adiabatic walls in multifamily dwellings; and, in Climate Zones 4 through 8, an air barrier at the interior vertical surface of insulation is recommended but not required in basement walls or crawlspace walls. For the purpose of these exceptions, a basement or crawlspace is a space for which ≥ 40% of the total gross wall area is below-grade.
ENERGY STAR Revision 08 requirements are required for homes permitted starting 07/01/2016.
Exhibit 2: DOE Zero Energy Ready Home Target Home. Certified under ENERGY STAR Qualified Homes Version 3. Infiltration (ACH50): Zones 1-2: 3; Zones 3-4: 2.5; Zones 5-7: 2; Zone 8: 1.5. Envelope leakage shall be determined by an approved verifier using a RESNET-approved testing protocol.
Standard Specification for Air Barrier (AB) Material or System for Low-Rise Framed Building Walls. This specification covers minimum performances and specification criteria for an air barrier material or system for framed, opaque walls of low-rise buildings. The provisions are intended to allow the user to design the wall performance criteria and increase air barrier specifications for a particular climate location, function, or design.
Table 402.4.2 Air Barrier and Insulation Inspection Component Criteria, Air barrier and thermal barrier: Exterior wall insulation is installed in substantial contact and continuous alignment with the air barrier. Air permeable insulation is not used as a sealing material.*
Table N1102.4.2 Air Barrier and Insulation Inspection Component Criteria, Air barrier and thermal barrier: Exterior wall insulation is installed in substantial contact and continuous alignment with the air barrier. Air permeable insulation is not used as a sealing material.*
Exterior insulation for framed walls is in substantial contact and continuous alignment with the air barrier.* Table R402.4.1.1 Air Barrier and Insulation Installation, Air barrier and thermal barrier: A continuous air barrier is installed in the building envelope including rim joists and exposed edges of insulation. Breaks or joints in the air barrier are sealed. Air permeable insulation is not used as a sealing material.*
Exterior insulation for framed walls is in substantial contact and continuous alignment with the air barrier.* Table N1220.127.116.11 Air Barrier and Insulation Installation, Air barrier and thermal barrier: A continuous air barrier is installed in the building envelope including rim joists and exposed edges of insulation. Breaks or joints in the air barrier are sealed. Air permeable insulation is not used as a sealing material.*
*Due to copyright restrictions, exact code text is not provided. For specific code text, refer to the applicable code.
Fully Aligned Air Barriers = Whole-House Draft Barrier