Reduced Thermal Bridging
All interior/exterior wall intersections insulated to the same R-value as the rest of the exterior wall*
Install insulation to run continuously behind interior/exterior wall intersections. Use one of the methods listed below or an equivalent assembly:
- Ladder blocking.
- Full length 2 x 6 or 1 x 6 nailer behind the first partition stud.
* All items of 4.4.5a-4.4.5e of the ENERGY STAR Thermal Enclosure System Rater Checklist must be installed to comply with ENERGY STAR.
Up to 10% of the total exterior wall surface area is exempted from the reduced thermal bridging requirements to accommodate intentional designed details (e.g., architectural details such as thermal fins, wing walls, or masonry fireplaces; structural details, such as steel columns). It shall be apparent to the Rater that the exempted areas are intentional designed details or the exempted area shall be documented in a plan provided by the builder, architect, designer, or engineer. The rater need not evaluate the necessity of the designed detail to qualify the home.
Mass walls utilized as the thermal mass component of a passive solar design (e.g., a Trombe wall) are exempt from this item. To be eligible for this exemption, the passive solar design shall be comprised of the following five components: an aperture or collector, an absorber, thermal mass, a distribution system, and a control system. For more information, visit the Energy Savers website.
Mass walls that are not part of a passive solar design (e.g., CMU block or log home enclosure) shall either utilize the strategies outlined in Item 4.4 (of the ENERGY STAR Thermal Enclosure System Rater Checklist). Or, the pathway in the assembly with the least thermal resistance, as determined using a method consistent with the 2009 ASHRAE Handbook of Fundamentals, shall provide ≥ 50% of the applicable assembly resistance, defined as the reciprocal of the mass wall equivalent U-factor in the 2009 IECC – Table 402.1.3. Documentation identifying the pathway with the least thermal resistance and its resistance value shall be collected by the rater and any Builder Verified or Rater Verified box under Item 4.4 (of the ENERGY STAR Thermal Enclosure System Rater Checklist) shall be checked.
Insulation shall run behind interior/exterior wall intersections using ladder blocking, full length 2- inch x 6-inch or 1-inch x 6-inch furring behind the first partition stud, drywall clips, or other equivalent alternative.
In stud-framed walls, where interior walls meet exterior walls, builders will typically use a conventional T-post detail. They will install two studs on the exterior wall, either touching each other or a few inches apart, at the location where the interior wall touches the exterior wall. The 2x4 stud at the end of the interior wall section is attached to these studs. If a few inches of space is left between these two exterior wall studs, insulation can be inserted in this space from outside before the exterior wall sheathing is installed; however, in practice the space rarely gets filled with insulation. This conventional framing method leaves uninsulated sections of exterior wall 3 to 6 inches in width everywhere an interior wall intersects an exterior wall.
Advanced framing techniques are described below that can be used to enable the installation of insulation along the exterior wall at the interior-exterior wall intersection.
These are some of several advanced wall framing techniques that can be employed by builders to increase energy savings by increasing insulation and reducing thermal bridging. Advanced framing also reduces costs by reducing lumber usage, materials waste, and labor time. See Minimum Wall Studs for more about advanced framing and for details on stud spacing and single top plates. Other advanced framing techniques are described in Insulated Corners, which explains how to construct corners with 2 studs instead of 3 studs to permit more insulation at the corners, Insulated Headers , which explains how and when to build open and insulated headers over windows and doors, and Minimal Framing at Doors/Windows for efficient framing around doors and windows.
Advanced framing techniques should be specified in the framer’s contract. Detailed framing elevations should be prepared after confirming permissibility in the local jurisdiction.
Figure 1 - The conventional T-post framing detail prevents insulation from being installed on the exterior wall at the interior-exterior wall intersection.
How to Install Advanced Framing at the Interior-Exterior Wall Intersections
There are three options: ladder blocking, use of a support post, or use of a connector plate and drywall clips.
1. Ladder Blocking
- Install short sections of 2x4s horizontally between the studs on the exterior wall on each side of the interior-exterior wall intersection. Install them flush with the interior surface of the exterior wall studs at a spacing of 24 inches apart.
- Attach the 2x4 interior wall to these blocking pieces.
- Install insulation behind the blocking.
2. Support Post
- Install a 1x6 or 2x6 support post on the exterior wall at the interior wall location, flush with the interior face of the wall. Attach it to the top plate and bottom plate.
- Attach the interior 2x4 wall to it.
- Insulate behind the post.
3. Connector Plate and Drywall Clips.
- Attach the interior 2x4 wall to the exterior wall top plate with a flat metal connector plate. Toenail the interior stud directly to the bottom plate.
b. Attach dry wall clips to the end stud of the interior wall to support drywall.
c. Insulate behind the post.
Advanced framing details should be specified in the construction plans and reviewed with framers. The construction supervisor should ensure that framing crews are knowledgeable of or trained in advanced framing techniques. The framing should be visually inspected by the site supervisor before the drywall is installed.
No climate specific information applies.
ENERGY STAR Version 3, (Rev. 6)
Thermal Enclosure Checklist, Reduced Thermal Bridging. Reduced thermal bridging at above-grade walls separating conditioned from unconditioned space (rim / band joists exempted) using advanced framing. All interior/exterior wall intersections insulated to the same R-value as the rest of the exterior wall. Insulation shall run behind interior / exterior wall intersections using ladder blocking, full length 2x6 or 1x6 furring behind the first partition stud, drywall clips, or other equivalent alternative.
DOE Challenge Home
Exhibit 1: Mandatory Requirements. Certified under ENERGY STAR Qualified Homes Version 3. Ceiling, wall, floor, and slab insulation shall meet or exceed 2012 IECC levels and achieve Grade 1 installation, per RESNET standards.
Advanced framing is not specifically addressed in the 2009 IECC.
Advanced framing is not specifically addressed in the 2012 IECC.