BASC Search | Building America Solution Center

Guide describing how to add spray foam insulation to the underside of the existing roof deck as part of the conversion of a vented attic to an unvented, insulated attic.

Attic Air Sealing, Insulating, and Ventilating for Ice Dam Prevention

Information guide describing proper attic air-sealing, insulation, and ventilation to combat ice dam formation on roofs in cold climate zones.

Insulating and Air Sealing Existing Non-ICAT Recessed Lights

Guide describing air-sealing of non-ICAT recessed lights installed in accessible attics of existing homes.

Right – Baffles maintain air flow above attic insulation

Air Sealing, Insulating, and Venting Attics and Roofs to Reduce Heat Gain

Information guide providing links to guides describing specific ways to air-seal, insulate, and ventilate attics and roofs to minimize heat gain in new and existing homes.

Right - Spray foam insulation has been sprayed onto the underside of the sloped roof and the gable end wall to provide a sealed, insulated attic for housing the HVAC ducts

Application of Spray Foam Insulation Under Plywood and OSB Roof Sheathing

Publication Date

July, 2015

Video describing how to air seal attic rafters with spray foam.

Sloped roof with cavity spray foam insulation, strapping, and gypsum board thermal barrier

Publication Date

Fri, 05/01/2015 - 12:00

Air-Impermeable Insulation for Condensation Control in Unvented Attics, per IRC Table 806.5.

Publication Date

Wed, 04/08/2020 - 12:00

A typical Las Vegas hot-dry climate home made of wood frame construction and insulated with R-25 expanded polystyrene externally over a drainage plane, with an unvented wood frame insulated attic and roof assembly.

Publication Date

Tue, 02/16/2010 - 12:00

Examples of many common ceiling penetrations that will be difficult to insulate and air seal in this cathedral ceiling.

Publication Date

Mon, 10/30/2006 - 12:00

Application of Spray Foam Insulation Under Plywood and Oriented Strand Board Roof Sheathing, BA-1312

Author(s)

Grin Aaron,

Smegal Jonathan,

Lstiburek Joseph W

Organization(s)

Building Science Corporation,

BSC

Publication Date

September, 2013

Report covering moisture and leakage issues associated with spray foam insulation application to the underside of roof sheathing.

Flat roof with cavity spray foam plus loose-fill insulation and gypsum board thermal barrier.

Publication Date

Fri, 05/01/2015 - 12:00

Spray foam insulation was installed on the underside of the roof deck and on gable end attic walls to create an unvented attic

Publication Date

Fri, 10/15/2021 - 12:00

The soffit dam and baffle allow air to flow through the vents without disturbing the insulation covering the top plates

Right - These raised heel roof trusses provide 16 inches of space over the outer walls for full insulation coverage at the attic perimeter.

Right – Sheathing extends to rafters adding strength to soffit, baffles keep attic insulation from vent to maintain air flow

Sloped roof with cavity spray foam insulation sprayed on underside of roof deck and covered with sprayed-on thermal or ignition barrier coating.

Publication Date

Fri, 05/01/2015 - 12:00

Right - This new sealed attic has 5.5 inches (R-20) of spray foam insulation along the underside of the roof deck providing a conditioned attic space for the heating and cooling ducts.

Wrong: Closed-cell spray foam roof insulation was not thick enough to meet IRC levels so the foam surface is colder than the dew point of the interior air and condensation formed on surface of the foam

Publication Date

Sun, 12/01/2013 - 12:00

Roof/Attic to Exterior Wall Air Control Upgrade

Guide outlining how to retrofit an exterior wall and/or attic to provide continuous air sealing.

Attic Knee Walls

Guide describing how to insulate and air-seal attic knee walls and floor joist cavities under knee walls.

Vented versus Unvented Attic

Guide describing options for designing and locating the thermal boundary at either the attic floor or along the roof line in new and existing homes.

Air Sealing Attic Access Panels/Doors/Stairs

Guide describing how to air-seal attic access panels, doors, and stairs to provide a continuous air barrier at the ceiling.

Condensation Control in Attics and Roofs in Cold Weather

Guide describing causes of condensation in attics and roof assemblies during cold weather and ways to reduce this condensation.

Air Sealing Drywall to Top Plate

Guide describing ways to seal drywall to the top plate of an exterior wall to air-seal the wall cavity.

Hybrid Assemblies, BSI-100

Author(s)

Lstiburek Joseph W

Organization(s)

Building Science Corporation,

BSC

Publication Date

October, 2017

Article describing issues with condensation in unvented attics insulated with open-cell spray foam.

De-Icing Ice Dams, BSI-097

Author(s)

Lstiburek Joseph W

Organization(s)

Building Science Corporation,

BSC

Publication Date

October, 2018

Article describing the importance of air sealing, insulation, and roof ventilation in reducing the likelihood of ice dam formation on roofs in cold snowy climates.

How to Prevent Roof Damage from Winter Ice Buildup

Author(s)

Dorsi Chris

Organization(s)

Montana State University Extension,

MSU Extension

Publication Date

January, 2019

Article from Montana State University Extension explaining how proper insulation techniques can greatly reduce the risks of ice dams on roofs in cold climate zones.

Wrong – Roof underlayment is not fully adhered and roof deck seams are not sealed so roof is susceptible to high-wind events

Right – Roof underlayment is fully adhered and roof deck seams are sealed so roof is resistant to high-wind events

Right - Open-cell polyurethane spray foam to R-28 on underside of roof turns new attic into conditioned space for HVAC.

Right – Closed-cell polyurethane foam is sprayed on the underside of the roof deck to provide structural connections and seal seams in the sheathing to increase wind resistance

The thermal boundary for a gable roof can be located at either a) the flat ceiling with a vented attic or b) the roof line for an unvented attic

New Whole-House Solutions Case Study: Imagine Homes: Stillwater Ranch, San Antonio, TX

Author(s)

Pacific Northwest National Laboratory

Organization(s)

PNNL

Publication Date

April, 2012

Case study describing a new home builder that strives to address health, safety, and durability issues in a hot and humid climate.

A low-sloped shed roof with the thermal boundary located at either a) the flat ceiling with a vented attic or b) the roof line for an unvented attic

A 1- and ½-story home with a room located in the attic and the thermal boundary located at either a) the walls and ceiling of the attic room with small vented attic spaces or b) the roof line for an unvented attic

Vulnerability of Vents to Wind-Blown Embers

Author(s)

Quarles Stephen L

Organization(s)

Insurance Institute for Business & Home Safety,

IBHS

Publication Date

August, 2017

Report covering the migration of wind-blown embers in roof vents.

Ping Pong Water and The Chemical Engineer, BSI-016

Author(s)

Lstiburek Joseph W

Organization(s)

Building Science Corporation,

BSC

Publication Date

October, 2016

Article outlining moisture accumulation in open cell spray polyurethane foam.

Cool Hand Luke Meets Attics, BSI-077

Author(s)

Lstiburek Joseph W

Organization(s)

Building Science Corporation,

BSC

Publication Date

July, 2015

Article describing the difference between conditioned or unvented attics and unconditioned or vented attics.

Cold Climate Building Techniques and Concepts: Cathedral Roofs

Publication Date

January, 2014

Author(s)

Cold Climate Housing Research Center

Organization(s)

CCHRC

Video describing roof and attic construction for cold climates, including cathedral roof design and insulation strategies, from Cold Climate Housing Research Center.

Right - Continuous wall sheathing and blocking has been installed to brace the raised heel trusses.

Publication Date

Sat, 10/01/2011 - 12:00

Attic Air Sealing Guide and Details, GM-1001

Author(s)

Lstiburek Joseph W

Organization(s)

Building Science Corporation,

BSC

Publication Date

February, 2010

Document providing background and approach for the prep work necessary prior to adding attic insulation - focusing on combustion safety, ventilation for indoor air quality, and attic ventilation for durability.

Radiant Barrier: Effect of Radiant Barriers on Heating and Cooling Bills

Author(s)

Oak Ridge National Laboratory

Organization(s)

ORNL

Publication Date

September, 2022

Fact sheet describing analysis of potential heating and cooling savings from radiant barriers in attics.

Measure Guideline: Guide to Attic Air Sealing

Author(s)

Lstiburek Joseph W

Organization(s)

Building Science Corporation

Publication Date

September, 2014

Guideline describing information and specifications relevant to air-seal existing attics.

Attic or Roof? An Evaluation of Two Advanced Weatherization Packages, BA-1205

Author(s)

Neuhauser Ken

Organization(s)

Building Science Corporation,

BSC,

National Renewable Energy Laboratory,

NREL

Publication Date

June, 2012

Report about a project that examines implementation of advanced retrofit measures in the context of a large-scale weatherization program and the archetypal Chicago, Illinois, brick bungalow.