Walls Adjoining Porch Roof
Install a rigid air barrier to separate the porch attic from the conditioned space.
- Install insulation in the exterior wall cavities without misalignments, compressions, gaps, or voids.
- Install a continuous rigid air barrier on the exterior side of the wall. Rigid air barrier materials could include rigid foam insulation, drywall, plywood, or OSB, among others.
- Seal the air barrier to the framing with a bead of caulk applied to the exterior face of the framing before installing the air barrier. 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.
- 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).
- 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.
- If this wall will not be hidden from view by a porch ceiling, then cover the wall with exterior siding.
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.
In two-story homes with covered porches, builders may sometimes forget to sheathe the wall area that will be hidden when the porch ceiling is installed, because the porch is framed before the wall sheathing is installed. If there is no exterior sheathing, blown insulation cannot be installed. Even if batt insulation is installed, if there is no exterior sheathing that is caulked in place to serve as an air barrier, the insulation is subject to wind washing from outside air, especially if the porch ceiling is vented or is not air tight.
In one-story homes with vented attics where the ceiling plane of the living space is level with the ceiling plane of the porch, the wall plane between the house attic and the porch attic does not need to be insulated and air sealed. In this case, the ceiling plane of the living space should be air sealed, especially along the top plate of the walls.
In one-story homes with unvented attics, the wall plane between the porch and the house should have a solid, sealed air barrier on the exterior side of the wall cavity and the wall cavity should be filled with insulation that is fully aligned to this air barrier.
The exterior sheathing that is hidden by the porch roof and ceiling can be rigid foam, OSB, plywood, or another rigid sheathing product, and it may be installed by framers or insulators. This task should be included in the contract for the appropriate trade depending on the workflow at the specific job site. Air barrier effectiveness is measured at the whole-house level. High-performance branding programs and the 2009 and 2012 IECC require that builders meet specified infiltration rates at the whole-house level. See the “compliance” tab for these specified infiltration rates.
Figure 2 - Building America researchers were called to investigate high heating bills at an apartment complex in Connecticut. (1) Infrared camera imagery revealed high heat loss on a second-story wall above a location where (2) a porch extended from the first-story exterior wall. (3) Researchers opened up the perforated vinyl porch ceiling to find (4) there was no air barrier covering the batt insulation. Air could flow through the insulation robbing it of its heating value. (5) An air barrier of rigid foam board was put in place with spray foam.
How to Install a Fully Aligned Air Barrier in a Porch Wall
- Install the exterior wall sheathing to extend to or beyond the porch roof rafters or install sheathing from the house attic side after porch roof framing is installed.
- or -
- If the drywall is already installed on the interior side of the wall, install insulation in the wall cavity. Make sure the insulation fully aligns with (is completely touching) the sheathing on the interior side.
2. Apply a thick bead of caulk to the framing that will be covered.
3. Cut wall sheathing (e.g., rigid foam insulation, OSB, or plywood) to cover the insulation on the exterior side of the wall cavity.
4. Nail or screw the sheathing in place over the caulk.
5. If there are seams in the sheathing, seal them with caulk or tape.
6. Install a porch ceiling or cover the wall sheathing with exterior siding.
A visual inspection should be made by the site supervisor to determine that the wall cavity separating the house from the porch attic is filled with insulation that is in full contact with the interior drywall and that the wall cavity is completely covered with rigid sheathing that is air sealed at all edges to form a continuous air barrier along the exterior wall of the house. Blower door testing, conducted in conjunction with inspection with an infrared camera, may also be useful in detecting air leakage or lack of insulation alignment at the porch wall.
Thermal Enclosure Checklist, Fully-Aligned Air Barriers. A complete air barrier shall be provided that is fully aligned with the insulation at exterior surface of walls in all climate zones; and also at interior surface of walls for Climate Zones 4-8.
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 4-87
2.4 Walls adjoining porch roofs or garages
Floors: At exterior vertical surface of floor insulation in all climate zones and, if over unconditioned space, also at interior horizontal surface including supports to ensure alignment. See Footnotes 10 & 11 for alternatives.9, 10, 11
2.7 All other floors adjoining unconditioned space (e.g., rim / band joists at exterior wall or at porch roof)
(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.
(9) EPA highly recommends, but does not require, an air barrier at the interior vertical surface of floor insulation in Climate Zones 4-8.
(10) Examples of supports necessary for permanent contact include staves for batt insulation or netting for blown-in insulation. Alternatively, supports are not required if batts fill the full depth of the floor cavity, even when compression occurs due to excess insulation, as long as the R-value of the batts has been appropriately assessed based on manufacturer guidance and the only defect preventing the insulation from achieving the required installation grade is the compression caused by the excess insulation.
(11) Alternatively, an air barrier is permitted to be installed at the exterior horizontal surface of the floor insulation if the insulation is installed in contact with this air barrier, the exterior vertical surfaces of the floor cavity are also insulated, and air barriers are included at the exterior vertical surfaces of this insulation.
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. Building envelope assemblies, including exterior walls and unvented attic assemblies (where used), shall comply with the relevant vapor retarder provisions of the 2012 International Residential Code.
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 N118.104.22.168 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