PNNL 2012. Building America Case Study Technology Solutions for New Homes: Attention to Detail in High-Performance Homes 2012. PNNL-SA-91087. Prepared by the Pacific Northwest National Laboratory for the U.S. Department of Energy Building America Program.
Shafts (e.g., Duct, Flue)
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Scope
Air Sealing
- Install a continuous rigid air barrier material to separate the exterior from the conditioned space.*
- Using a saw or drill, cleanly cut all penetrating holes no more than 1 inch larger in diameter than the penetrating object to allow for proper air sealing.
- Seal all gaps, and holes to unconditioned space with caulk or foam. Fibrous insulation is not an air barrier and cannot be used for sealing gaps.
- Use high temperature caulking along with flashing or UL-rated collars. Install them continuously around all combustion flues while maintaining proper clearance from combustion materials.
*ENERGY STAR recommends using a rigid air barrier, but it is not a requirement.
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Description
Install air barriers around duct and flue shafts in the attic floor to prevent air leakage between the living space and the attic and to allow full insulation levels to be installed around the duct or flue. Air barrier material around duct shafts can include thin sheet goods such as rigid insulation, dry wall, OSB, or plywood. Air barriers around flue shafts should be made of a heat-resistant material such as sheet metal. 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 specific job sites.
Air barrier effectiveness is measured at the whole-house level. High-performance branding programs and the IECC code require that builders meet specified infiltration rates at the whole-house level. See the “compliance” tab for these specified infiltration rates.
How to Seal a Duct Boot to the Ceiling
1. Seal all sides of the duct boot to the gypsum board with spray foam or caulk. Apply mastic or metal tape to all duct seams and joints.
Figure 1 - Spray foam air seals the boot to the ceiling 
2. Add insulation to the specified attic insulation depth.
Figure 2 - Caulk air seals the boot to the ceiling
How to Seal a Rigid Duct Chase
1. Install wood framing cross pieces in the attic rafter bays on each side of the duct chase, if needed.
Figure 3 - Install wood framing cross pieces in the attic rafter bays on each side of the duct chase
2. Seal all wood framing joints surrounding the chase with sealant. Lay a generous continuous bead of sealant along the top edge of the chase framing.
Figure 4 - Seal all wood framing joints surrounding the chase with sealant and lay a bead of sealant along top edge of chase framing
3. Measure and cut the air-blocking material (plywood, rigid foam, or drywall) to fit around the duct. Place the blocking material on the framing leaving a 1/4-in. gap between the rigid duct and the material. Fasten the material in place with nails or screws. Seal the material to the duct with sealant. Also seal any joints in the blocking material. Cover the material with insulation to the specified attic insulation depth.
Figure 5 - Cut plywood, rigid foam, or drywall to fit around duct. Fasten to framing and caulk edges and seams
How to Air Seal a Flex Duct Chase
1. Install wood framing cross pieces in the attic rafter bays on each side of the duct chase, if needed.
Figure 6 - Install wood framing cross pieces in the attic rafter bays on each side of the duct chase
2. Seal all wood framing joints surrounding the chase with sealant. Lay a generous continuous bead of sealant along the top edge of the chase framing.
Figure 7 - Seal all wood framing joints surrounding the chase with sealant and lay a bead of sealant on top edge of chase framing
3. Measure and cut the air-blocking material (plywood, rigid foam, or drywall) to fit around the duct. Cut the material into two halves and then cut half circles in each to encompass the flex duct. Place the blocking material on the framing and in contact with the duct. Fasten the material with nails or screws. Seal the blocking material to the duct with sealant. Also seal the joints in the blocking material. Cover the blocking material with insulation to the required levels.
Figure 8 - Cut plywood, rigid foam, or drywall to fit around duct. Fasten to framing and caulk edges and seams
How to Air Seal a Metal Chimney or Flue Vent Pipe – Option 1 – Air Seal at the Bottom of the Framing
1. Cut two pieces of sheet metal to cover the chase opening. Allow 1 inch of overlap. Fasten the sheet metal to the framing and seal all edges and seams with fire-rated caulk.
Figure 9 - Ceiling opening for chimney chase
Figure 10 - Cut sheet metal to cover the chase opening. Fasten sheet metal to framing and seal edges with fire-rated caulk
2. Use sheet metal to make a shield that will wrap around the pipe with a 3-inch clearance. Fold in the tabs at the top and every other tab at the bottom to maintain a 3-inch clearance. With tabs folded, the shield should be 4 inches taller than the finished insulation level. Seal the edges together with fire-rated caulk.
Figure 11 - Form a sheet metal shield around the flue pipe
3. Cover the shield with insulation to the required height. The insulation should cover the rafters.
Figure 12 - Fill area around shield with insulation
How to Air Seal a Metal Chimney or Flue Vent Pipe – Option 2 – Air Seal at the Top of the Framing
1. Cut two pieces of framing lumber equal in height to the ceiling joists. Fasten wood cross pieces to joists keeping at least 3 inches of clearance to the pipe. Caulk this wood blocking to the framing.
Figure 13 - Ceiling opening for chimney pipe chase
Figure 14 - Cut wood blocking to frame in flue pipe
2. Cut two pieces of sheet metal or aluminum flashing to fit around the chimney pipe with 1 inch of overlap. Fasten the sheet metal to the framing and seal all edges and seams with fire-rated caulk.
Figure 15 - Cut sheet metal to fit around flue, fasten to wood blocking, and seal with caulk
3. Use sheet metal to make a shield that will wrap around the pipe with a 3-inch clearance. Fold in tabs at the top and every other tab at the bottom to maintain a 3-inch clearance. With tabs folded, the shield should be 4 inches taller than finished insulation level. Seal the edges together with fire-rated caulk.
Figure 16 - Form sheet metal shield around pipe keeping 3-inch clearance
4. Cover the shield with insulation to the required height.
Figure 17 - Cover shield with insulation to required attic insulation height
Ensuring Success
Blower door testing, which is conducted as part of the whole-house energy performance test-out, may help indicate whether duct and flue openings to unconditioned space (such as an attic) have been successfully sealed. An infrared camera can be used in conjunction with the blower door testing to detect air leakage and heat loss at the duct and flue shaft openings, if a sufficient temperature difference exists between the unconditioned and the conditioned space of the house. An experienced technician can also check for air leaks beneath the knee walls with a smoke pencil or by feeling with the back of the hand.
Climate
No climate specific information applies.
Right and Wrong Images
Presentations
None Available
Videos
None Available
CAD Images
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SourceBuilding Plans for the ENERGY STAR Thermal Bypass Checklist
Green Building Advisor. 2011. Building Plans for the ENERGY STAR Thermal Bypass Checklist. Green Building Advisor, Newtown, Connecticut, The Tanton Press.
Organization:Green Building AdvisorSaveDownloadDownload PDFDownload PDF -
SourceBuilding Plans for the ENERGY STAR Thermal Bypass Checklist
Green Building Advisor. 2011. Building Plans for the ENERGY STAR Thermal Bypass Checklist. Green Building Advisor, Newtown, Connecticut, The Tanton Press.
Organization:Green Building AdvisorSaveDownloadDownload PDFDownload PDF
Compliance
ENERGY STAR Version 3, (Rev. 6)
Thermal Enclosure Checklist, Air Sealing. Penetrations to unconditioned space fully sealed with solid blocking or flashing as needed and gaps sealed with caulk or foam.
DOE Challenge Home
Exhibit 1: Mandatory Requirements. Certified under ENERGY STAR Qualified Homes Version 3.
2009 IECC
Section 402.4.1 Building thermal envelope. Joints (including rim joist junctions), attic access openings, penetrations, and all other such openings in the building envelope that are sources of air leakage are sealed with caulk, gasketed, weatherstripped or otherwise sealed with an air barrier material, suitable film or solid material.*
Section N1102.4.1 Building thermal envelope. Joints (including rim joist junctions), attic access openings, penetrations, and all other such openings in the building envelope that are sources of air leakage are sealed with caulk, gasketed, weatherstripped or otherwise sealed with an air barrier material, suitable film or solid material.*
2012 IECC
Table R402.4.1.1 Air Barrier and Insulation Installation, Shafts/penetrations: Duct shafts, utility penetrations, and flue shafts opening to exterior or unconditioned space are air sealed.* Table R402.4.1.1, 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.*
Table N1102.4.1.1 Air Barrier and Insulation Installation, Shafts/penetrations: Duct shafts, utility penetrations, and flue shafts opening to exterior or unconditioned space are air sealed.* Table N1102.4.1.1, 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.
Case Studies
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Attention to Detail in High-Performance Homes 2012
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David Weekley Homes: Eagle Springs & Waterhaven, Houston, TX
PNNL. 2012. Building America Case Study: David Weekley Homes, Eagle Springs & Waterhaven, Houston, TX. PNNL-SA-87333, prepared by the Pacific Northwest National Laboratory for the U.S. Department of Energy Building America Program.
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Tommy Williams Homes: Longleaf Village & Belmont, Gainesville, FL
PNNL. 2012. Building America Case Study: Tommy Williams Homes, Longleaf Village & Belmont, Gainesville, FL. PNNL-SA-87331, prepared by the Pacific Northwest National Laboratory for the U.S. Department of Energy Building America Program.
References
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2009 IECC—International Energy Conservation Code
2009 IECC, International Energy Conservation Code. International Code Council, Washington, D.C.
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2009 IRC—International Residential Code for One and Two Family Dwellings
2009 IRC, International Residential Code for One and Two Family Dwellings. 2009. Fifth Printing. International Code Council, Washington, D.C.
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2012 IECC—International Energy Conservation Code
2012 IECC, International Energy Conservation Code. International Code Council, Washington, D.C.
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2012 IRC—International Residential Code for One and Two Family Dwellings
2012 IRC, International Residential Code for One and Two Family Dwellings. 2012. Second Printing. International Code Council, Washington, D.C.
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DOE Challenge Home National Program Requirements
DOE. 2012. DOE Challenge Home National Program Requirements (Rev. 02). Office of Energy Efficiency and Renewable Energy, U.S. Department of Energy, Washington, D.C.
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ENERGY STAR Qualified Homes, Version 3 (Rev. 06) Inspection Checklist for National Program Requirements
EPA. 2012. ENERGY STAR Qualified Homes, Version 3 (Rev. 06) Inspection Checklist for National Program Requirements. U.S. Environmental Protection Agency, Washington, D.C.
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Guide to Attic Air Sealing
Lstiburek, J. 2010. Guide to Attic Air Sealing. Prepared by the Building Science Corporation for the U.S. Department of Energy, Building America Program.
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Thermal Enclosure System Rater Checklist Guidebook
EPA. 2011. Thermal Enclosure System Rater Checklist Guidebook. U.S. Environmental Protection Agency, Washington, D.C.
