Log in or register to create Field Kits and Sales Worksheets. Why register?

Insulating Existing Floors over Garage

Scope

Upgrade a garage ceiling when a portion of the interior of the house is located directly above the attached garage by adding insulation and air sealing as follows:

  • Install insulating rigid foam sheathing to the underside of the existing garage ceiling, which typically has a finished surface of gypsum board or lath and plaster, or directly to the underside of the ceiling joists if the garage has an unfinished ceiling and the joist cavities are exposed. If the joist cavities are exposed, the layer of insulating sheathing will need to be foil-faced polyisocyanurate or XPS and the sheathing should be detailed to serve as the air control layer with seams taped and edges caulked or taped.
  • Install blocking for reinstallation of existing services and attachments on the ceiling.

The U.S. Department of Energy’s Standard Work Specifications has additional information on insulating floors over garages.

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

Adding insulating rigid foam sheathing to a garage ceiling can improve the comfort of floors above an attached garage and increase air sealing between the garage and the house. The insulating sheathing can be installed over an existing ceiling (Figures 1 to 3) or if there is no ceiling the foam can be attached directly to the ceiling joists.

Either way, a layer of gypsum board must be installed to cover the insulating sheathing for fire protection. If the ceiling cavity lacks insulation, additional blown or batt insulation can be installed prior to installing the insulating sheathing and gypsum board.

Other recommendations for insulating and air sealing a garage ceiling when there is living space above the garage can be found in the guides Floor Above Garage and Air Sealing Attached Garage.

Rigid foam insulating sheathing installed over an existing garage ceiling with a new gypsum board fire protection layer installed over the foam
Figure 1. Rigid foam insulating sheathing installed over an existing garage ceiling with a new gypsum board fire protection layer installed over the foam.

Rigid foam insulating sheathing installed over an existing garage ceiling that is first air sealed with caulk
Figure 2. Rigid foam insulating sheathing installed over an existing garage ceiling that is first air sealed with caulk.

Rigid foam insulating sheathing installed over an existing garage ceiling with retrofits to air seal exterior wall before adding exterior wall insulating sheathing
Figure 3. Rigid foam insulating sheathing installed over an existing garage ceiling with retrofits to air seal exterior wall before adding exterior wall insulating sheathing.

How to Insulate a Garage Ceiling

  1. Inspect the existing garage ceiling.  If ceiling drywall is in place, patch and air seal at seams and around existing penetrations as needed to establish a robust air control layer, as shown in Figures 1 to 3. Blow in loose-fill cavity insulation if desired.
  2. ALTERNATELY, if the ceiling joists are exposed, install either loose-fill with netting, batt, or spray foam cavity insulation.
  3. Install blocking for re-installation of existing services and attachments on the ceiling.
  4. Install insulating sheathing (foil-faced polyisocyanurate, XPS or EPS Type II) as shown in Figures 1 to 3.  Install over existing ceiling gypsum board or if there is not existing gypsum board, then attach directly to ceiling joists. If the ceiling joists are exposed or the existing garage ceiling is removed, the layer of insulating sheathing must be foil-faced polyisocyanurate or XPS and should be installed as the air control layer, so all seams should be taped and sealant should be applied around all wiring and other penetrations
  5. Install 5/8 inch Type X gypsum board or equivalent as the ceiling covering. Mud and tape seams.

Ensuring Success

For a house with an attached garage, air leakage from the garage to the conditioned space of the home through the garage walls or ceiling can draw unwanted pollutants into the home.  Steps should be taken to ensure that the health of the occupants will not be compromised by the retrofit. Airtightness of all walls, ceilings, and doors that are common between the attached garage and the interior of the house should be verified and improved, if needed. Fire protection must be provided as required by the current adopted building code.

Ensure the air control layer of the garage ceiling is continuous.

Maintain a proper ratio of vapor and air impermeable to vapor and air permeable insulation. 

For information on interface of attached garages with a common wall, see Rigid Foam Insulation between Existing House and Garage Walls.

Climate

In house designs where there is living space above the garage, the garage ceiling should be treated as the floor assembly of the rooms above and should be designed for a specific hygrothermal region, rain exposure zone, and interior climate. The climate zones are shown on the map below, which is taken from Figure C301.1 of the 2012 IECC. 

IECC climate zones
IECC Climate Zone Map

The insulation levels should be based on the minimum requirements for vapor control in the current adopted building code and the minimum requirements for thermal control in the current energy code. (See Table R601.3.1 Class III Vapor Retarders of the 2009 IRC (ICC 2009a) and Table R702.7.1 Class III Vapor Retarders of the 2012 IRC (ICC 2009b).  Additional insulation can be added above these minimums to create high R-Value floor assemblies. The table below provides the minimum thermal resistance (R-value) requirements for framed floors specified in the 2009 IECC (ICC 2009b) and the 2012 IECC (ICC 2012b), based on climate zone.

Framed Floor R-Value Requirements in the 2009 and 2012 IECC
Table 1. Framed Floor R-Value Requirements in the 2009 and 2012 IECC

Training

Right and Wrong Images

None Available

Presentations

None Available

Videos

None Available

CAD Images

None Available

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

[Note: Guidance for Version 3.0, Revision 08 is coming soon.]

ENERGY STAR Certified Homes is a voluntary high-performance home labeling program for new homes operated by the U.S. Department of Energy and the U.S. Environmental Protection Agency. Builders and remodelers who are conducting retrofits are welcome to seek certification for existing homes through this voluntary program.

ENERGY STAR Certified Homes (Version 3.0, Revision 07) requires that ceiling, wall, floor, and slab insulation levels meet or exceed those specified in the 2009 International Energy Conservation Code (IECC).

If the state or local residential building energy code requires higher insulation levels than those specified in the 2009 IECC, you must meet or exceed the locally mandated requirements. Some states have adopted the 2012 IECC. Visit the U.S. DOE Building Energy Codes Program to see what code has been adopted in each state. For states that have adopted the 2012 IECC or an equivalent code, EPA intends to implement the ENERGY STAR Certified Homes Version 3.1 National Program Requirements for homes permitted starting one year after state-level implementation of the 2012 IECC or an equivalent code. However, EPA will make a final determination of the implementation timeline on a state-by-state basis. Some states and regions of the country have ENERGY STAR requirements that differ from the national requirements. Visit ENERGY STAR’s Regional Specifications page for more information on those region-specific requirements.

The ENERGY STAR Thermal Enclosure System Rater Checklist (Ver 3, Rev 07) specifies:

2.1 Ceiling, wall, floor and slab insulation levels shall comply with one of the following options:

2.1.1 Meet or exceed 2009 IECC levels, OR

2.1.2 Achieve <= 133% of the total UA resulting from the U-factors in 2009 IECC Table 402.1.3, excluding fenestration and per guidance in note “d” below, AND home shall achieve <= 50% of the infiltration rate in Exhibit 1 of the National Program Requirements.

2.2 All ceiling, wall, floor, and slab insulation shall achieve RESNET-defined Grade I installation or, alternatively, Grade II for surfaces that contain a layer of continuous, air impermeable insulation ≥ R-3 in Climate Zones 1 to 4, ≥ R-5 in Climate Zones 5 to 8.

3 Fully-Aligned Air Barriers. At each insulated location noted below, a complete air barrier shall be provided that is fully aligned with the insulation as follows:

  • At interior or exterior surface of ceilings in Climate Zones 1-3; at interior surface of ceilings in Climate Zones 4-8. Also, include barrier at interior edge of attic eave in all climate zones using a wind baffle that extends to the full height of the insulation. Include a baffle in every bay or a tabbed baffle in each bay with a soffit vent that will also prevent wind washing of insulation in adjacent bays
  • At exterior surface of walls in all climate zones; and also at interior surface of walls for Climate Zones 4-8 7
  • At interior surface of floors in all climate zones, including supports to ensure permanent contact and blocking at exposed edge

3.1.8 Garage rim / band joist adjoining conditioned space

3.2.1 Floor above garage

3.3.2 All other ceilings.

DOE Zero Energy Ready Home 

The DOE Zero Energy Ready Home Program is a voluntary high-performance home labeling program for new homes operated by the U.S. Department of Energy. Builders and remodelers who are performing retrofits on existing homes are welcome to seek certification for those homes through this voluntary program.

The U.S. Department of Energy Zero Energy Ready Home National Program Requirements specify as a mandatory requirement (Exhibit 1, #2.2) that, for all labeled homes, whether prescriptive or performance path, ceiling, wall, floor, and slab insulation shall meet or exceed 2012 IECC levels. See the guide 2012 IECC Code Level Insulation – DOE Zero Energy Ready Home Requirements for more details.

2009 IECC

Section 402.4 Air leakage (Mandatory).

Section 402.4.1 Building Thermal Envelope.

Section 402.4.2 Air sealing and insulation.

Section 402.4.5 Recessed lighting.

Table 402.4.2 Air Barrier and Insulation Inspection Component Criteria

20122015, and 2018 IECC

Section R402.4 Air leakage (Mandatory).

Section R402.4.1 Building Thermal Envelope.

Section R402.4.5 Recessed lighting.

Table R402.4.1.1 Air Barrier and Insulation Installation

Retrofit: 200920122015, and 2018 IECC

Section R101.4.3 (Section R501.1.1 in 2015 and 2018 IECC). Additions, alterations, renovations, or repairs shall conform to the provisions of this code, without requiring the unaltered portions of the existing building to comply with this code. (See code for additional requirements and exceptions.)

2009 IRC

Table R302.6 Dwelling/Garage Separation.

Section R302.5 Dwelling/garage opening/penetration protection.

Section R302.6 Dwelling/garage fire separation.

Section R315.2 Where required in existing dwellings.

Table 702.3.5 Minimum thickness and application of gypsum board.

Section N1102.4 Air leakage (Mandatory).

Section N1102.4.1 Building Thermal Envelope.

Section N1102.4.2 Air sealing and insulation.

Table N1102.4.2 Air Barrier and Insulation Inspection Component Criteria

 20122015, and 2018 IRC

Section R302.5 Dwelling/garage opening/penetration protection.

Section R302.6 Dwelling/garage fire separation.

Table R302.6 Dwelling/Garage Separation.

Section R315.3 Where required in existing dwellings. (Location in 2015 and 2018 IRC)

Table 702.3.5 Minimum thickness and application of gypsum board.

Section N1102.4 Air leakage (Mandatory).

Section N1102.4.1 Building Thermal Envelope.

Table N1102.4.1.1 Air Barrier and Insulation Installation

Retrofit: 200920122015, and 2018 IRC

Section N1101.3 (Section N1107.1.1 in 2015 and 2018 IRC). Additions, alterations, renovations, or repairs shall conform to the provisions of this code, without requiring the unaltered portions of the existing building to comply with this code. (See code for additional requirements and exceptions.)

Appendix J regulates the repair, renovation, alteration, and reconstruction of existing buildings and is intended to encourage their continued safe use.

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.

Case Studies

None Available

References and Resources*

  1. Author(s): International Code Council
    Organization(s): ICC
    Publication Date: January, 2009

    Code establishing a baseline for energy efficiency by setting performance standards for the building envelope (defined as the boundary that separates heated/cooled air from unconditioned, outside air), mechanical systems, lighting systems and service water heating systems in homes and commercial businesses.

  2. Author(s): International Code Council
    Organization(s): ICC
    Publication Date: January, 2009

    Code for residential buildings that creates minimum regulations for one- and two-family dwellings of three stories or less. It brings together all building, plumbing, mechanical, fuel gas, energy and electrical provisions for one- and two-family residences.

  3. Author(s): International Code Council
    Organization(s): ICC
    Publication Date: January, 2012

    Code establishing a baseline for energy efficiency by setting performance standards for the building envelope (defined as the boundary that separates heated/cooled air from unconditioned, outside air), mechanical systems, lighting systems and service water heating systems in homes and commercial businesses.

  4. Author(s): International Code Council
    Organization(s): ICC
    Publication Date: January, 2012

    Code for residential buildings that creates minimum regulations for one- and two-family dwellings of three stories or less. It brings together all building, plumbing, mechanical, fuel gas, energy and electrical provisions for one- and two-family residences.

  5. Author(s): Pettit, Neuhauser, Gates
    Organization(s): Building Science Corporation
    Publication Date: July, 2013

    Guidebook providing useful examples of high performance retrofit techniques for the building enclosure of wood frame residential construction in a cold and somewhat wet climate.

Contributors to this Guide

The following authors and organizations contributed to the content in this Guide.

Building Science Corporation, lead for the Building Science Consortium (BSC), a DOE Building America Research Team

Last Updated: 12/16/2015