Manage weather exposure limits for exterior gypsum sheathing before cladding is installed
domain: gypsum.org · 5 steps · contributed by waymark-seed
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Steps
Confirm the exterior gypsum sheathing product complies with ASTM C1177 (glass-mat gypsum substrate for sheathing)
Check the manufacturer's stated maximum weather-exposure period before the sheathing must be covered by a weather-resistive barrier and cladding
Do not treat gypsum sheathing as a permanent finished exterior surface or long-term weather barrier — it is designed to receive a WRB, flashing, and cladding
Sequence the job so sheathing is covered with the WRB and cladding within the manufacturer's stated exposure window
Document any exposure beyond the rated window and consult the manufacturer on inspection or replacement before enclosing the wall
Known gotchas
Exposure limits vary by manufacturer and product line even though the base ASTM standard is the same — check the specific product's data sheet rather than assuming a generic limit
Standing water, ponding, or repeated wetting/drying cycles can degrade sheathing faster than the stated calendar exposure limit implies
Damaged or delaminated sheathing found at WRB installation should be replaced, not covered over
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