Description

Sealed (also called unvented) attics are insulated at the roof deck while the ceiling plane is uninsulated. Sealed attics areusually not directly conditioned, but instead the conditions float between indoor and outdoor temperature conditions.The moistureperformance of sealed attics has been investigated using a whole house hygrothermal simulation model to understand the risksfor high moisture content in the roof sheathing and for high humidity in the attic. The results have also been validated againstfield test data. The analyzed shingled roof decks have been insulated either with open-cell spray foam or air-permeable insulation(fibrous insulation). The concept of the air-permeable insulation to perform as the condensation-control layer is analyzed.

A parametric study was carried out varying attic air leakage both to the indoors and outdoors, water leakage to roof sheathing,vapor permeance of the insulation, as well as the indoor air-moisture loads and exterior climate. The results show that the sealedattic can experience elevated humidity at warm temperatures which can create favorable conditions for mold growth unless theattic is intentionally conditioned or via duct air leaks. The vapor permeance of the insulation layers (and if a vapor-retardingcoating is present) was a key factor that controlled the moisture content of the roof sheathing together with the overall airtightness.The air impermeable but vapor permeable insulation was not sufficient alone to prevent condensation in the roof deck.

Presented at Thermal Performance of Exterior Envelopes of Whole Buildings XII, December 2013

Citation: Thermal Performance of Exterior Envelopes of Whole Buildings XII

Product Details

Published:

2013

Number of Pages:

13

File Size:

1 file , 5.1 MB

Product Code(s):

D-BldConf13-64