Skylight Shaft Walls
Scope
Install insulation and an air barrier around skylight shafts.
- If non-rigid insulation is used in the wall cavities of the skylight shaft, install a rigid air barrier on the exterior side of the shaft wall framing to prevent the cavity insulation from sagging and to create a continuous thermal barrier.
- Seal all seams, gaps, and holes in the air barrier with caulk or foam. Rigid air barrier material could include rigid foam insulation, drywall, plywood, or OSB, among others.
- 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.
- 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).
See the Compliance Tab for related codes and standards requirements, and criteria to meet national programs such as DOE’s Zero Energy Ready Home program, ENERGY STAR Certified Homes, and Indoor airPLUS.
Description
When skylights are installed, special attention must be paid to insulating the vertical shafts extending from the roof to the ceiling. Unsealed attics are often insulated along the attic floor with blown fiberglass or cellulose insulation. A different type of insulation will need to be installed along the skylight shaft walls, one that will maintain full alignment (or contact) with the back side of the sheathing for the height of the skylight shaft walls and that will maintain at least the minimum required depth of insulation along the full height. Skylight shaft walls should be insulated to the same R-value as other exterior walls if the attic they pass through is not insulated.
There are several options for insulating skylight shafts. One option to consider, especially if several skylights are being installed, is to make the attic part of the conditioned space of the home by installing insulation at the roof deck, either by spray foaming along the underside of the roof deck or installing rigid foam above the roof deck, or by constructing the roof with structural insulated panels (SIPs). This insulated attic would also provide a conditioned space for any HVAC equipment installed in the attic.
If the skylight shafts are installed in a vented, uninsulated attic, then the sides of the skylight shaft should be insulated. This can be accomplished using spray foam or rigid foam, or by constructing the shaft walls with SIPs. Fiberglass batt insulation is not recommended for insulating the skylight shaft walls because it can settle or pull away from the wall. If batt insulation is used, it should be covered with a rigid material such as rigid foam, which will provide an interior air barrier and ensure that the batts will not slide down or fall away from the wall. These materials may be installed by insulators, framers, or subcontractors or vendors hired specifically to install the skylight. This task should be included in the contract for the appropriate trade depending on the workflow at the specific job site.
How to Insulate a Skylight Shaft
- Select the skylight size and location to avoid cutting roof or ceiling rafters, if possible. (House designs that use 24-in on-center fully aligned framing members are less likely to require cutting of studs for skylight installation.) Follow the manufacturer’s instructions to install the skylight on the roof deck, properly flashing and integrating the skylight frame with roofing materials to minimize the risk of water intrusion. The roof opening is framed with headers, with framing lumber run horizontally across the opening and securely nailed to the rafters to support the structure.
- Install headers across the ceiling opening as you did for the roof opening, using a single header at each end if no ceiling joists are cut or double headers if a ceiling joist has to be cut. If the light shaft will be flared, cut the joist at the angle of the flare.
- Cut 2x4 studs (or 2x6 to allow for more cavity insulation) for the corners of the light shaft, angled on each end to fit flush against the rafters and ceiling joists. Next, place studs 24-inch on-center around the opening. Nail 2x2 cleats to the inside edges of the corner studs or use drywall clips to serve as backing for the drywall.
Or, frame the shaft with structural insulated panels (SIPs) following the manufacturer’s instructions for air sealing the corners, seams, and top and bottom edges.
- Fill the stud cavities with spray foam, batt insulation, or rigid foam (Figures 1 and 2). Next, cover them with a layer of rigid foam to achieve the R-value level required for your climate zone.
Or, nail rigid foam in place over the studs and fill the cavities with blown cellulose or blown fiberglass.
- Caulk drywall and rigid foam to framing at all edges. Seal any seams in the rigid foam with caulk, tape, or foam.
- Paint drywall with latex paint to serve as the vapor barrier.
Figure 1- Frame, insulate, and air seal the walls of the skylight shaft as you would an exterior wall 
Figure 2 - Non-rigid cavity insulation should be covered with a rigid air barrier that is sealed at the edges
How to Insulate a Solar Tube
- Install the tube according to the manufacturer’s instructions.
- Insulate the solar tube with plastic-covered flex duct insulation.
- Or - Wrap the tube with unfaced fiberglass batt insulation. Secure the insulation in place with ties. Cover the unfaced batt insulation with flexible foil-faced insulation and secure it with ties and metal tape.
- Use spray foam or caulk to air seal the solar tube to the ceiling from above.
- Caulk under the decorative ring on the room side of the ceiling.
For more on installing solar tubes, see the guide Light Tubes.
Ensuring Success
An infrared camera can be used to detect heat loss around the skylight. The insulation installation should be visually inspected by the site supervisor.
Climate
ENERGY STAR Certified Homes
ENERGY STAR Certified Homes (Ver. 3/3.1 Ver 08) Rater Field Checklist, A complete air barrier that is fully aligned with insulation is installed at the exterior vertical surface of wall insulations in all climate zones and also at the interior vertical surface of walls in Climate Zones 4-8.
DOE Zero Energy Ready Home
DOE Zero Energy Ready Home (Rev 05)Exhibit 2: DOE Zero Energy Ready Home Target Home. Infiltration: Climate Zones 1-2: 3 ACH 50; Zones 3-4: 2.5 ACH50; Zones 5-7: 2 ACH50; Zone 8: 1.5 ACH50. Envelope leakage shall be determined by an approved verifier using a RESNET-approved testing protocol.
Training
Right and Wrong Images
Videos
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Publication Date: July, 2015Courtesy Of: Risinger HomesVideo describing how to insulate skylight shafts and knee walls correctly.
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CAD Images
Compliance
The Compliance tab contains both program and code information. Code language is excerpted and summarized below. For exact code language, refer to the applicable code, which may require purchase from the publisher. While we continually update our database, links may have changed since posting. Please contact our webmaster if you find broken links.
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
2.3 Attic knee walls and skylight shaft walls8
Footnotes:
(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.
(8) Exterior air barriers are not required for attic knee walls that are ≤ 24 in. in height if an interior air barrier is provided and insulation extends in all directions from the top of this interior air barrier into unconditioned space at the following levels: CZ 1-5: ≥ R-21; CZ 6-8: ≥ R-30.
ENERGY STAR Revision 08 requirements are required for homes permitted starting 07/01/2016.
DOE Zero Energy Ready Home (Rev 05) Exhibit 1: Mandatory Requirements: Item 1, Homes must be certified under ENERGY STAR Qualified Homes Version 3. Item 2, Ceiling, wall, floor, and slab insulation shall meet or exceed 2012 or 2015 IECC levels.
Exhibit 2: Design the home to meet the HERS index of the DOE Zero Energy Ready Home Target Home, for which insulation levels must meet the 2012 IECC and achieve Grade 1 installation, per RESNET standards.
Exhibit 2: Infiltration: Climate Zones 1-2: 3 ACH 50; Zones 3-4: 2.5 ACH50; Zones 5-7: 2 ACH50; Zone 8: 1.5 ACH50. 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.
Self-Adhered Sheet Air Barrier. 2006. Air Barrier Association of America, Walpole, MA. This specification for self-adhered sheet air barriers is developed by a professional association, the Air Barrier Association of America, to provide guidance to the design professional.
Fluid-Applied Air and Vapor Barrier. 2012. Air Barrier Association of America, Walpole, MA. This specification for air barriers that are fluid-applied and also act as vapor barriers is developed by a professional association, the Air Barrier Association of America, to provide guidance to the design professional.
Closed Cell, Medium-Density Spray Polyurethane Foam Air Barrier. 2011. Air Barrier Association of America, Walpole, MA. This specification for closed cell, medium-density spray polyurethane foam air barriers is developed by a professional association, the Air Barrier Association of America, to provide guidance to the design professional.
Fluid-Applied Vapor Permeable Air Barrier. 2012. Air Barrier Association of America, Walpole, MA. This specification for fluid-applied vapor permeable air barriers is developed by a professional association, the Air Barrier Association of America, to provide guidance to the design professional.
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.* 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.*
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.* 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.*
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.*
Table N1102.4.1.1 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.*
Table R402.1.2 Insulation and Fenestration Requirements – meet or exceed the insulation levels listed in this table.
Table R402.4.1.1 Air Barrier and Insulation Installation, Walls: Insulation in exterior framed walls is in substantial contact and continuous alignment with the air barrier. Windows, Skylights, and Doors: the space between skylights and framing must be sealed. General requirements: A continuous air barrier is installed in the building envelope; breaks and joints in the air barrier are sealed. Air-permeable insulation is not used as an air-sealing material.*
Section R402.4.1.2 Testing. The building should be tested for air leakage in accordance with ASTM E 779 or E 1827 and should have an air leakage rate of ≤ 5 in CZ 1 and 2 or ≤ 3 in CZ 3-8.
N1102.4.1.1 Air Barrier and Insulation Installation, Walls: Insulation in exterior framed walls is in substantial contact and continuous alignment with the air barrier. Windows, Skylights, and Doors: the space between skylights and framing must be sealed. General requirements: A continuous air barrier is installed in the building envelope; breaks and joints in the air barrier are sealed. Air-permeable insulation is not used as an air-sealing material.*
*Due to copyright restrictions, exact code text is not provided. For specific code text, refer to the applicable code.
This Retrofit tab provides information that helps installers apply this “new home” guide to improvement projects for existing homes. This tab is organized with headings that mirror the new home tabs, such as “Scope,” “Description,” “Success,” etc. If there is no retrofit-specific information for a section, that heading is not included.
SCOPE
Insulate and air seal the shaft walls of an existing skylight.
- Inspect the existing skylight for signs of water leakage; repair flashing and replace damaged framing as necessary.
- Choose an air barrier material - either rigid insulation, drywall, or sprayed polyurethane foam insulation.
- If the air barrier will be rigid insulation or drywall, remove any existing insulation if insufficient or sagging. Fill the skylight shaft framing cavities with unfaced batt insulation. Caulk framing then cover with rigid insulation or drywall. Tape and seal all joints in the rigid insulation or drywall.
- If the air barrier will be sprayed polyurethane foam, remove any existing insulation and fill the cavities with either open- or closed-cell spray foam.
- Follow the steps in the Description tab.
For more information on conditions that may be encountered when working with walls in existing homes, see the assessment guide on attics.
See the U.S. Department of Energy’s Standard Work Specifications for more on air sealing and insulation skylights. Follow safe work practices as described in the Standard Work Specifications.
DESCRIPTION
Retrofit an existing skylight shaft by adding an air barrier and insulation to the shaft walls. This work will be performed from the attic side of the skylight shaft, typically using rigid insulation or drywall or sprayed polyurethane foam insulation. If the air barrier will be rigid insulation or drywall, the framing cavities should be filled with insulation. Unfaced fiberglass batt insulation is typical, but almost any unfaced cavity insulation may be used as long as it will remain in place with minimal settling. Where sprayed polyurethane foam (SPF) insulation is used as the air barrier, follow the applicable code requirements regarding the use of a thermal or ignition barrier. Sometimes this barrier is a coating that is sprayed directly onto the surface of the SPF. In other cases material such as drywall is used as the thermal barrier to separate the SPF from adjacent construction.
This work will be performed from inside the attic so use safe work practices and be aware of hazardous conditions as described in the attic assessment guide.
How to Insulate and Air Seal Skylight Shaft Walls
- Inspect the existing skylight for signs of water leakage, such as water stains and rot. Repair skylight flashing (from the roof exterior) and replace any damaged framing as necessary.
- Set aside existing attic floor insulation to expose the framing at the base of the skylight shaft to be air sealed.
- Determine what material will constitute the air barrier around the shaft wall - typically either rigid insulation, drywall, or sprayed polyurethane foam insulation.
- If using rigid foam or drywall as the air barrier:
- Remove any existing insulation in framing cavities around the skylight shaft if it is insufficient, wet, sagging, or pest infested. If the insulation is unfaced batt in good shape and of sufficient quantity, leave it in place.
- Install new unfaced batt insulation as needed to completely fill the framing cavities of the skylight shaft.
- Apply a thick bead of caulk to the face of framing at the top, bottom, and sides on each side of the shaft.
- Nail or screw the rigid insulation or drywall in place over the caulked framing, as shown in the Description tab. Tape and seal all joints in the rigid insulation or drywall.
- If the air barrier to be used is sprayed polyurethane foam (SPF) insulation, remove any old insulation and fill the cavities of the skylight framing with the SPF. Both open- and closed-cell SPF insulations are acceptable in any climate zone for this application.
- Replace floor insulation around the base of the skylight shaft.
More Info.
Access to some references may require purchase from the publisher. While we continually update our database, links may have changed since posting. Please contact our webmaster if you find broken links.
Fully Aligned Air Barriers = Whole-House Draft Barrier
A whole-house draft barrier is a continuously connected layer of solid or air-tight materials that block air leaks. This barrier can also function as part of a water barrier, thermal barrier, and vapor barrier, if the location and materials are compatible. For example, rigid foam insulation can provide a combined function. Rigid foam sheets can be used to block air flow when seams are sealed with tape, caulks or adhesives, or liquid applied sealants. An example of an interior air barrier may be the drywall on the home’s walls and ceilings, when the seams are taped and mudded, and caulk, spray foam, or gaskets are used to seal around wiring, plumbing, and other penetrations. Insulation should be in full contact with the air barrier layer.
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