Attic mold removal in Cary, NC

What attic mold looks like

Attic mold usually shows up as black, gray or dark green staining on the underside of the roof sheathing, the plywood or OSB the shingles are nailed to. It is often heaviest on the north side of the roof, near the eaves and around bathroom fan outlets. Other clues are white fuzzy growth on rafters, nail tips that are rusty or frosted in winter, damp or matted insulation and a musty smell when the attic hatch opens.

Why attics grow mold

Mold in an attic is almost always a moisture problem that started in the house below:

• Bath and kitchen fans venting into the attic. Code requires exhaust to go outdoors, but many fans end in the attic, or their flexible duct has come loose and is blowing shower steam onto the rafters.
• Air leaks from the house. Warm, moist air rises through recessed lights, the attic hatch, plumbing and wiring holes and the tops of interior walls.
• Ventilation that does not work. Insulation blown over the soffit vents, too little intake for the exhaust vents, or a powered fan pulling conditioned air out of the house.
• Roof leaks. Cracked rubber boots around plumbing vents, flashing at chimneys and walls, and valleys.
• HVAC equipment in the attic. Ducts and air handlers sweat in summer when their insulation is thin or torn, and a clogged condensate drain can overflow the pan.
• Dryer vents that are disconnected or end in the attic.

Winter and summer patterns

In winter, the roof deck gets cold at night, especially on the north side that sees little sun. Moist air leaking up from the house condenses on it, the wood stays damp for days at a time, and mold grows. In a Triangle summer, the attic is hot, but anything cold up there, such as an uninsulated supply duct or a sweating air handler, collects water from the humid air, and mold follows wherever that water drips. Knowing which pattern you have points straight at the fix.

How attic mold is removed

1. Fix the cause first, whether that means ducting a bath fan to the roof, sealing air leaks, clearing soffits or repairing the roof.
2. Contain the attic access and protect the living space below, with HEPA air filtration running.
3. Remove the growth from the sheathing and rafters. Light growth is HEPA vacuumed and wiped; heavier growth is sanded or wire brushed; large attics are often soda blasted or dry ice blasted, which strip mold from wood without soaking it.
4. Treat and seal. An antimicrobial is applied to the cleaned wood, and some jobs add a mold-resistant coating. A coating never goes over growth that has not been removed.
5. Replace insulation that is wet, moldy or crushed, and restore the depth.

Sheathing that is delaminated or soft is replaced, usually alongside the roofer.

Fixing ventilation and air leaks

Removal without prevention buys a season or two. Lasting fixes usually include sealing the gaps between the house and the attic before adding insulation, installing baffles so soffit vents can breathe, balancing intake and exhaust ventilation, and running every exhaust fan through an insulated duct to its own roof or wall cap. If the HVAC system lives in the attic, its ducts and drain are checked too; mold in air ducts and HVAC covers that side.

Attic mold and selling a house

“Microbial growth on roof sheathing” is a common line on Triangle inspection reports, and it tends to come up during a buyer’s due diligence period, when time is short. Sellers can get ahead of it with an inspection before listing. Buyers can get a remediation quote, with the cause identified, so the negotiation is about a real number. If the mold came from a bathroom fan, bathroom mold removal covers the bathroom side of the fix.