BASC Search | Building America Solution Center

Unvented Attic Insulation

Guide describing methods for insulating an unvented attic along the roof line.

Attic Eave Minimum Insulation

Guide providing guidance on insulating attic eaves in new and existing single-family homes and multifamily buildings.

Unvented Insulated Sloped Roofs

Guide describing construction of sloped roofs that are unvented and are insulated above the roof deck.

Detail of an unvented cathedralized attic showing air-impermeable spray foam insulation plus batt insulation installed on the underside of the roof deck.

Below Deck Spray Foam Insulation for Existing Roofs

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.

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

Unvented Conditioned Attic with Spray Foam Insulation Below Roof Deck

Guide describing a method for insulating an unvented attic by spraying foam insulation along the underside of the roof deck.

How To Strengthen Your Home for Under $10,000 – Insulated Concrete Forms

Publication Date

September, 2014

Video interview explaining the benefits of installing insulated concrete forms for both energy efficiency and disaster resistance in either new or existing homes for under $10,000. Recommendations from FLASH Strong Homes.

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

Publication Date

Fri, 05/01/2015 - 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

Ice dams formed by melting of snow on roofs can affect roofs, walls, ceilings, siding, and insulation.

Publication Date

Mon, 02/04/2013 - 12:00

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

Lack of insulation over the top plate can lead to ice dam formation on a low sloped roof.

Publication Date

Mon, 10/30/2006 - 12:00

Step 1. Apply roof underlayment over roof deck and up the sidewall over the rigid foam insulation

Reference

40% Whole-House Energy Savings in the Marine Climate, Volume 11

Author(s)

Baechler Michael C,

Gilbride Theresa L,

Hefty Marye G,

Cole Pam C,

Williamson Jennifer,

Love Pat M

Organization(s)

Pacific Northwest National Laboratory,

PNNL,

Oak Ridge National Laboratory,

ORNL,

U.S. Department of Energy,

DOE

Report providing builders in marine climates with guidance for building homes that have whole-house energy savings of 40% over the Building America benchmark with no added overall costs for consumers.

Publication Date

Wed, 09/01/2010 - 12:00

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

Step 5. Apply self-adhesive flashing over top edge of the wall flashing, diverter, and rigid foam insulation

Reference

40% Whole-House Energy Savings in the Marine Climate, Volume 11

Author(s)

Baechler Michael C,

Gilbride Theresa L,

Hefty Marye G,

Cole Pam C,

Williamson Jennifer,

Love Pat M

Organization(s)

Pacific Northwest National Laboratory,

PNNL,

Oak Ridge National Laboratory,

ORNL,

U.S. Department of Energy,

DOE

Report providing builders in marine climates with guidance for building homes that have whole-house energy savings of 40% over the Building America benchmark with no added overall costs for consumers.

Publication Date

Wed, 09/01/2010 - 12:00

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

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

A dormer with an openable window (not shown) can provide access to the roof if flood waters rise too high and too quickly; the dormer should be properly insulated, flashed, and air sealed

Roof/Attic to Exterior Wall Air Control Upgrade

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

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.

Construct Roofs and Attics for Ice Dam Prevention

Guide describing how ice dams form and how roofs can be constructed to prevent them.

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.

Rocks Don’t Burn, BSI–068

Author(s)

Lstiburek Joseph W

Organization(s)

Building Science Corporation,

BSC

Publication Date

May, 2013

Report covering non-combustible continuous exterior insulation and non-combustible roof venting.

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.

How To: Mounting Solar on Sips

Author(s)

Sughrue Patrick

Organization(s)

Premier SIPS Structural Insulated Panels,

Home Power Magazine

Publication Date

September, 2013

A structural insulated panel (SIP) roof has no embedded lumber in the structure, and therefore nothing substantial for attaching PV array and solar hot water mounts. Single or double lumber splines could be put into the panels, or I-joists at 4-foot intervals could be added.

Installation of Drip Edge over Underlayment for Hurricane Zones

Provide flashing and sealing integrated with the air and water control layers for vents and other roof penetrations

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

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

Low-Slope ("Flat") Roofs

A guide describing how to install low-sloped ("flat") roofs with insulation above the roof deck that resist wind pressures during high-wind events.

Roof Escape Openings for Flood-Prone Areas

Guide describing options for providing access to the roof via openable skylights, dormer windows, or roof hatches, for occupants of homes in areas prone to severe flooding.

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.

Typical Concrete Tile Roofs in Florida

Hurricane Straps

Publication Date

September, 2020

Author(s)

FLASH Strong Home

Organization(s)

FLASH

Video describing hurricane ties and how they make your home more ready for severe weather by strengthening structural connections.

This home has heat loss through the roof, leading to ice dam formation and structural issues during winter months.

Publication Date

Mon, 02/04/2013 - 12:00

Flashing of Penetrations in Existing Roofs

Guide describing how to provide a continuous water control layer across the roof assembly by sealing all penetrations for pipes, vents, etc. in existing roofs.

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.

Water management details for a roof drain installed along with rigid foam on a flat roof

Publication Date

Fri, 05/01/2015 - 12:00

IRC FAQ: Conditioned Attics, GM-0905

Author(s)

Building Science Corporation

Organization(s)

BSC

Publication Date

May, 2009

Report discussing how to create livable space in the attic that meets IRC code requirements by either creating a ventilated roof assembly, or and unvented attic assembly.

Designing Houses That Keep Their Cool

Author(s)

Wilson Alex

Organization(s)

Green Building Advisor

Publication Date

July, 2013

Article from Green Building Advisor on strategies to take when building homes to reduce the need for air conditioning, including insulation, windows, site selection, and roofing.

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: Deep Energy Enclosure Retrofit (DEER) for Zero Energy House (ZERH) Flat Roofs

Author(s)

Loomis Honorata,

Pettit Betsy

Organization(s)

Building Science Corporation,

BSC

Publication Date

May, 2015

This Measure Guideline provides design and construction information for a deep energy enclosure retrofit solution of a flat roof assembly.

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.

How Many Hours-of-Safety Do Our Homes Have in Extreme Weather?

Author(s)

Corvidae Jacob,

Ayyagari Sheha

Organization(s)

Rocky Mountain Institute,

RMI

Publication Date

July, 2019

Article from RMI on how climate change is leading to an increase in critical extreme heat hours and what smart building strategies can be taken to mitigate some of these effects including paint color and insulation.

Disaster-Resistant Roof Venting

Guide describing the installation of roof vents that are resistant to damage from high winds and entry of wind-borne rain, wildfire embers, or pests.

Attic Ventilation Fans

Guide describing the use of attic ventilation fans to mechanically pull outside air through the attic in an attempt to cool the attic, control moisture, and prevent ice dams.

Roof Eaves Sealed with Self-Adhering Membrane in Cold Climates

Guide describing how to apply heavy membranes at eaves in cold climates to help guard against ice dams.

Creating a Cool Room for Extreme Heat Events

Guide describing how to create a designated shelter-from-heat space in a home to help occupants successfully weather an extreme heat event.

Step and Kick-Out Flashing at Roof-Wall Intersections

Guide describing how to install step and kick-out flashing on roofs.

Roof Deck Sheathing and Sealing for Sloped Roofs

Guide describing requirements for sheathing and sealing the roof decking in accordance with the requirements of the IBHS Fortified Home Program's Hurricane and High Wind Standards, and other roofing considerations to increase the roof's disaster resistance.