As the cold weather approaches, we would like to remind everyone about the concerns raised in our 2011 Winter Advisory Alert “Construction Generated Moisture” that related to both occupancy- and construction-generated moisture. If you are involved with reroofing an existing facility, take a moment to verify with the building owner or roofing consultant that consideration has been given to the need for an air/vapor barrier to prevent moisture-related issues.
During the construction of new buildings, moisture accumulation is influenced by construction practices, project scheduling, membrane color, roof insulation (single versus multiple layers), the lack of air/vapor barriers, and lack of building dehumidification prior to its occupancy.
In the absence of air or vapor barriers, warm humid air migrates upward during cold weather and infiltrates the roofing assembly through gaps, unsealed joints or around penetrations. Moisture within the humid air will begin condensing once it encounters a surface temperature below the dew point.
White or light-colored roofs, due to their reflectivity, often fall below the dew point and remain below the dew point for longer periods than darker roofs, and are therefore more prone to the phenomenon of condensation issues and moisture drips.
When considering the use of cool or reflective membranes in colder climate regions, think beyond the single component strategy. Utilize appropriate insulation levels in multiple layers and air/vapor barriers.
It is important to take several steps to reduce the probability of condensation, especially if using a light-colored roofing membrane in colder northern climates;
- Evaluate the construction practices being followed and assess their impact on the roofing assembly
- Consider building dehumidification to lower moisture levels
- Incorporate the use of air/vapor barriers to prevent humid air from reaching the roof assembly/ the cold membrane
- Seal gaps/joints in the deck, around penetrations and junctions between the deck and a parapet wall or curb when an air/vapor barrier is not used
- Use multiple layers of insulation with staggered joints to obstruct humid air from gaining access to the cold underside surface of the membrane
- Use at least the minimum ASHRAE recommended R-values
- Specify a darker membrane like EPDM to minimize energy consumption and carbon emissions in colder weather
To avoid the potential issues raised in this advisory, Carlisle recommends that you discuss them with the building owner, general contractor and project designer.
Please direct any questions or concerns to the Carlisle Design Services team or the Project Review group at 1-800-479-6832.
Click here to read the complete advisory.
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