Standard Active Last Updated: Apr 11, 2025 Track Document
ASTM E3258-25

Standard Guide for Evaluation of Changes to the Thermal, Moisture and Ventilation Performance of Existing Roof Enclosures (with Vented or Sealed Attic or Rafter Spaces)

Standard Guide for Evaluation of Changes to the Thermal, Moisture and Ventilation Performance of Existing Roof Enclosures (with Vented or Sealed Attic or Rafter Spaces) E3258-25 ASTM|E3258-25|en-US Standard Guide for Evaluation of Changes to the Thermal, Moisture and Ventilation Performance of Existing Roof Enclosures (with Vented or Sealed Attic or Rafter Spaces) Standard new BOS Vol. 04.12 Committee E06
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Significance and Use

5.1 Energy conservation is being addressed more often on existing or historically significant buildings, or both, originally constructed with uninsulated or unconditioned roof enclosures, or both. Renovations or retrofits of existing buildings that include altering the roof enclosure or changing the ambient conditions within the attic or enclosed rafter space(s) or conditioned spaces below the roof enclosure can have major unintended impacts on the performance of the roof enclosure. Without proper evaluation, changes to the thermal and moisture properties of the roof enclosure or changes to the ventilation and conditioning of the space below the roof enclosure could have serious negative impacts, particularly on the integrity of the existing structure, and the potential for condensation and other moisture accumulation related issues. This standard seeks to provide guidance on how to evaluate such changes and alterations.

5.1.1 Alterations to Ventilation—Any time the ventilation within a roof enclosure is altered, the impact on the roof deck, roof framing members, and roof covering materials should be assessed. Some roof enclosures have protected openings (such as soffit vents or ridge vents) specifically intended to provide ventilation along the underside of the roof deck. However, other buildings have been constructed with no intent to be airtight and featured natural ventilation achieved through voids or the inherent gaps and seams in the construction of the roof deck, eaves, and construction techniques which did not seek to provide an airtight building enclosure. Reducing or eliminating the natural drying potential of these roof enclosures by adding vapor retarders, air barriers, or eliminating natural ventilation (for example, converting to an unvented attic or to enclosed rafter spaces) may lead to accumulation of moisture vapor or increase the moisture content within the existing roof decks, attic spaces, or structural framing members, which could cause structural degradation or reduce the service life of these building components. The role and importance of roof enclosure ventilation in managing moisture, moisture vapor, temperature, and condensation is discussed in Appendix X1.

5.1.2 Alterations to Thermal Resistance Directly Below the Roof Deck—Any time additional insulation is added to a roof enclosure, particularly when added to the underside of the roof deck, the impacts on the roof deck and structural framing members should be assessed. Many older and historic buildings feature roof enclosures that have little to no existing insulation. Energy conservation is being addressed more often on existing and historically significant buildings constructed with these traditional roof enclosures. Without proper evaluation, changes to the thermal and moisture properties of these roof enclosures could have serious negative impacts. Altering the thermal gradient across the roof enclosure by adding insulation below the roof deck can have unintended effects. Addition of thermal insulation reduces heat flow and negatively impacts the drying potential of the assemblies by reduction in heat flow. Specifically, the moisture content of the existing roof deck and structural supports is of concern when insulation is added to the underside of the roof deck. Although installation of insulation to the underside of the deck may present challenges or concern regarding roof decks or roof coverings (for example, when converting to an unvented attic condition or to enclosed rafter spaces), creative design techniques may permit adding insulation below-deck while maintaining a ventilation space immediately below the roof deck.

5.1.3 Alterations to Attic or Interior Ambient Conditions—Any time the temperature or relative humidity, or both, immediately below a roof enclosure or within the attic space of a roof enclosure is altered, the impacts on the roof deck and the structural framing members should be assessed. It is common practice for owners or designers to upgrade existing buildings by adding modern HVAC systems while seeking to prevent excessive energy losses through the attic. A common project goal is to bring the roof and attic space up to current energy code with respect to insulation and air barriers. Additionally, the presence of mechanical equipment, sprinkler systems, or other specialized equipment within the attic space often results in the need to condition portions of, or the entire, attic space. This could have implications on the performance of the roof enclosure.

5.1.4 Addition of Vapor Retarders—Adding any vapor impermeable material to an originally vapor permeable roof enclosure has the potential to alter the hygrothermal performance of the overall roof enclosure. This may lead to an unintended accumulation of moisture which would not have occurred prior to the addition of any impermeable material, whether the material is intended to serve the function of a vapor retarder or not.

Scope

1.1 This guide covers the evaluation of hygrothermal impacts to existing roof enclosures resulting from roof enclosure alterations or changes to the interior environment. Examples of alterations that may affect the hygrothermal performance include but may not be limited to: installation of or alterations to insulation, installation of air or vapor retarders, alterations to the ventilation openings of naturally ventilated attic space or installing mechanical attic ventilation, or any other alterations that could impact the drying potential, ventilation, thermal performance, or vapor resistance of the roof enclosure. Examples of interior environment changes that may affect the hygrothermal performance include but are not limited to: changes in occupancy, mechanical conditioning of a previously unconditioned space, adding habitable space within an existing attic space, or any other alteration that will impact the temperature, relative humidity, or air flow beneath the existing roof deck.

1.2 This guide is intended to address the hygrothermal impacts of a retrofit to an existing roof enclosure which originally contained naturally ventilated or unconditioned attic or rafter spaces.

1.3 This guide can be used as a part of an evaluation to assess the cause of moisture-related issues impacting the structure beneath an existing roof enclosure suffering from moisture accumulation related issues, including impacts on roof rafters, trusses, and joists.

1.4 This guide is not intended to address the installation, maintenance, or replacement of roof covering materials.

1.5 This guide does not include provisions for structural evaluation of the existing roof enclosure. Changes to the roof loads, including dead and live loads, need to be evaluated outside of the provisions of this guide.

1.6 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety, health, and environmental practices and determine the applicability of regulatory limitations prior to use.

1.7 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.

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Details
Book of Standards Volume: 04.12
Developed by Subcommittee: E06.24
Pages: 9
DOI: 10.1520/E3258-25