Skylight Shaft Walls

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Climate

ENERGY STAR Version 3, (Rev. 07)

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.

DOE Challenge Home

Exhibit 2: DOE Challenge 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.

climate zone map

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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 insulate the entire attic, either by spray foaming along the underside of the roofline 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

  1. 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.
  2. 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.
  3. 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.

  1. Fill the stud cavities with spray foam, batt insulation, or rigid foam. 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.

  1. Caulk drywall and rigid foam to framing at all edges. Seal any seams in the rigid foam with caulk, tape, or foam.
  2. Paint drywall with latex paint to serve as the vapor barrier.

Frame, insulate, and air seal the walls of the skylight shaft as you would an exterior wall

Figure 1- Frame, insulate, and air seal the walls of the skylight shaft as you would an exterior wall  Reference

Non-rigid cavity insulation should be covered with a rigid air barrier that is sealed at the edges

Figure 2 - Non-rigid cavity insulation should be covered with a rigid air barrier that is sealed at the edges Reference

How to Insulate a Solar Tube

  1. Install the tube according to the manufacturer’s instructions.
  2. Insulate the solar tube with plastic-covered flex duct insulation.
  3. 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.
  4. Use spray foam or caulk to air seal the solar tube to the ceiling from above.
  5. Caulk under the decorative ring on room side of the ceiling.

Ensuring Success

An infrared camera can be used to detect heat loss around the skylight, if a sufficient temperature difference exists between the attic and the conditioned space of the house. The insulation installed should be visually inspected by the site supervisor.

Scope

Skylight shaft walls

Fully Aligned Air Barriers

  1. If non-rigid insulation is used, install a rigid air barrier to prevent insulation from sagging and create a continuous thermal barrier.
  2. Seal all seams, gaps, and holes of the air barrier with caulk or foam.
  3. Install the insulation without any misalignments, compressions, gaps, or voids so that it acts as both the air barrier and thermal boundary. Examples include foam board, spray foam or dense pack insulation. 

ENERGY STAR Notes:

ENERGY STAR highly recommends using a rigid air barrier, but it is not a requirement.

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. ENERGY STAR recommends, but does not require, rigid air barriers. Open-cell or closed-cell foam shall have a finished thickness >= 5.5 inches or 1.5 inches, 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 inch 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.

ENERGY STAR highly recommends, but does not require, inclusion of an interior air barrier at band joists in Climate Zone 4 through 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. All insulated ceiling surfaces, regardless of slope (e.g., cathedral ceilings, tray ceilings, conditioned attic roof decks, flat ceilings, sloped ceilings), must meet the requirements for ceilings.

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Compliance

ENERGY STAR Version 3, (Rev. 07)

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. 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.

DOE Challenge Home

Exhibit 2: DOE Challenge 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. 

ASTM E1677-11

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.

ABAA 07261

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.

ABAA 07262

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.

ABAA 07263

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.

ABAA 07265

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.

 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.* 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.*

2009 IRC

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.*

2012 IECC

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.*

2012 IRC

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.*

*Due to copyright restrictions, exact code text is not provided.  For specific code text, refer to the applicable code.

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References and Resources*

  1. Author(s): DOE
    Organization(s): DOE
    Publication Date: June 2013

    Standard requirements for DOE's Challenge Home national program certification.

  2. Author(s): EPA
    Organization(s): EPA
    Publication Date: June 2013

    Standard document containing the rater checklists and national program requirements for ENERGY STAR Certified Homes, Version 3 (Rev. 7).

  3. Author(s): EPA
    Organization(s): EPA
    Publication Date: October 2011

    Guide describing details that serve as a visual reference for each of the line items in the Thermal Enclosure System Rater Checklist.

Last Updated: 08/15/2013

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