Attic Mold Removal in Bellevue, WA —
Sheathing Assessed Panel-by-Panel, Source Identified

Cold-climate zones: winter condensation from interior air infiltrating attic floor gaps. Hot-humid zones: summer outdoor air moisture infiltrating attic via inadequate ventilation. Both scenarios worsened by exhaust fan termination inside attic. Cause determines correction.

Sapstain from lumber mill organisms (typically Ophiostoma species) appears as uniform blue-black or grey-black staining flat on the wood surface — it's actually in the wood fiber from the milling and drying process, present before the panel was installed. It doesn't have visible surface texture, white or grey hyphal fringe, or fuzzy growth patterns. Active mold colonies have surface texture, may have white or grey sporulating fringe, and are associated with elevated MC% in the panel. We confirm by measuring MC% at sapstained panels — consistently low MC% (below 14%) in a dry attic confirms non-active status; elevated MC% indicates active growth associated with current moisture conditions. Lab surface sampling can confirm when visual and moisture data don't give a clear answer.

Most attic sheathing with surface mold colonization — panels with MC% within the treatable range (elevated but below the threshold where structural decay is occurring), without physical delamination or loss of rigidity — can be treated in place with HEPA removal of loose spore material and penetrating borate application. This is the appropriate protocol for surface colonization on structurally sound panels. Replacement is required for panels with physical structural delamination (OSB losing layer cohesion) or through-penetration of decay fungi (the structural panel is softening or punky). We assess each panel individually — replacement is specified by panel location, not assumed for all darkened panels.

An exhaust fan terminates inside the attic when the installer ran the flex duct from the fan housing but didn't connect it to an exterior penetration — leaving the duct end loose inside the attic, or connecting to a gap between sheathing panels. Every time the fan runs, it deposits the full moisture load from bathroom steam directly onto the attic framing and sheathing above the bathroom. For a bathroom with a 50 CFM fan running 20 minutes per shower, that's a significant daily moisture addition directly onto cold attic framing. Proper exterior termination requires insulated flex duct (to prevent condensation inside the duct), properly connected at both the fan housing and a correctly-sized exterior wall, soffit, or roof cap.

Treatment products applied to structural wood only — sheathing and rafters. Not applied to roofing materials. SDS sheets available for manufacturer warranty review. Sheathing replacement panels requiring roofing material removal coordinated with your roofing contractor.