Attic Black Mold and How to Prevent or Stop it from Growing


If you had a chance to read “Attic Black Mold and Why is it Growing in Your Attic” (you can quickly watch the short video below), it’s now time to continue attic evaluation.

Attic black mold does not necessarily cause your house environment contamination, but under some conditions it might.

However, attic black mold usually becomes an issue when discovered during the home inspection. In addition, depending on the contamination extent, correcting the problem could make a significant hole in your budget.

In case the black mold has already contaminated your attic, I will show you how to stop it from further spreading. If there is no mold, just follow the same guideline to ensure that everything is the way it should be.

Remember – if you are not sure how to do it – find somebody else comfortable with accessing the attic. It is not worth the risk of getting seriously injured! The best time to inspect the attic and determine if it is functioning properly is during the coldest winter days.

Attic black mold - properly insulated attic access panel

How to prevent attic black mold #1

You should have attic access panel / pull down stairs insulated to minimize air transfer between the living area and the attic. Roof-decking section located above the attic entrance might be your first encounter with attic black mold.

Pre-cut piece of a blanket insulation glued to the hatch will do the job – if it has a paper facing (or any other vapor retarder type), apply paper to the hatch material surface. If using any other materials – make sure that they are not flammable and can be exposed.

For pull-down stairs, people sometimes make a square / hinged / insulated box that opens up into the attic after the stairs are open.

Attic black mold cause - missing kitchen vent section in attic areaAttic black mold cause - missing bathroom vent discharge pipeAttic mold cause - disconnected bathroom vent discharge pipeAll dryer / kitchen / bathroom vents must discharge to the house exterior and beyond the attic area – they are huge sources of warm, humid air, which feeds the attic black mold growth if trapped under the roof.

How to prevent attic black mold #2

If you are looking at the attic section located directly above the bathroom and / or kitchen with an exhaust fan discharging through the ceiling, you should be able to see some kind of a pipe/duct (galvanized steel, aluminum, or plastic – no plastic for the kitchen vent!) between the attic floor and the roof decking.

If there is no pipe, and you cannot see the fan enclosure itself, turn it on before you step into the attic, and try to locate it by following the sound, exhaust fan might be under the layer of insulation.

House attic black mold - bathroom exhaust fan discharging into the soffit causing mold growth on the roof deckingHouse attic black mold - bathroom exhaust fan discharging into the soffit causing mold growth on the roof deckingThere is a chance that vent discharge pipes are in the soffit or connected to the vent ports installed inside the soffit. Personally, I don’t recommend such installations and for one very simple reason – they are often responsible for the attic black mold growth.

During the cold season warm air will return to the attic through the soffit vents (some jurisdictions permit it and even recommend such installation). So, if there’s no pipe attached to the vent, or one discharging through the soffit appears to be causing black mold growth (stains / discoloration above the soffit area where the pipe enters), remove the vent pipe from the soffit.

Extend it through the roof using a dedicated port or at least install it close to the attic vent (just make sure that vent screen is clean).

Attic black mold - kitchen vent must have a dedicated port, attic roof vent should not be used for this purposeKitchen vents should have dedicated ports (don’t use attic ventilation ports), and smooth interior, single wall, galvanized steel pipes should be used for discharge, not plastic or aluminum flexible hoses.

How to prevent attic black mold #3

Disconnected dryer vent in attic area might result in attic black mold growthAttic black mold - lint contaminated dryer vent on roof surfaceA dryer vent discharging into the attic is a huge source of moisture and heat – requires its own dedicated port (just like the kitchen vent). Again, smooth interior wall metal pipe should be used (no plastic permitted and flexible aluminum not recommended).

Dryer vents require periodical cleaning

to remove accumulated lint from interior walls – when it becomes clogged, you’re just wasting precious energy and creating a fire hazard – if it penetrates the roof, it would probably be easier to separate the discharge pipe in the attic area (at roof vent connection) and clean pipe and roof vent screen from there.

Clogged dryer vent pipes overheat and if pipe connections have been sealed / secured with regular duct tape, they might eventually separate. This would allow for warm and moist air discharge into the attic, thus creating a perfect environment for attic black mold. Do not use screws on connections, they simply trap more lint inside, so plastic ties and heating ducts aluminum tape / aluminum foil tape + regular maintenance is the best choice.

How to prevent attic black mold #4

Missing skylight chase walls insulationAttic mold - missing attic floor insulation

Any missing insulation on skylight chases, walls / ceiling between the attic and living quarters should be installed – with blanket type insulation always put moisture barrier / vapor retarder (paper, plastic, aluminum, etc.) facing towards the heated area – never leave flammable paper exposed.

Improperly installed attic floor insulation - exposed flammable paper and double vapor retarderAttic mold - vapor retarder facing should be always applied toward heated areaIf you’re planning to install additional insulation on top of the existing one, make sure that there’s only one vapor retarder – example: if an existing insulation has a paper facing, you should not install another paper faced insulation layer on top of the old one.


Attic mold - open chase around the chimney at the attic floor penetration is a significant source of heat and should be properly sealed

There might be an open chase / empty wall space between the basement / crawlspace and attic area – seal it, from both sides if possible (around the chimney flue pipe – use metal fire-stop/radiation shield and proper clearances to framing and insulation). If it is a duct supplying combustion air to the furnace / utility room containing gas burning appliances – it must remain open and unobstructed.

How to prevent attic black mold #5
Attic black mold - cathedral ceiling insualtion without required 2 inch spacing to decking (cold climate)Attic mold - 2 inch separation between the insulation and roof decking for proper air circulationCathedral ceilings insulation – Cathedral ceilings insulation – it has to be installed with a proper clearance to decking surface (2″). Without that clearance that allows for air circulation, mold might start growing on the roof-decking surface.

How to prevent attic black mold #6

Plumbing vent pipe left open in attic area, and should continue through the roofPlumbing vents terminating in the attic area – extend them through the roof, repair or replace cracked plumbing vent pipes. Sewer gases vapor adds additional unwanted moisture to the attic which can condensate on decking, start dripping onto your ceiling, and become breeding ground for the attic black mold.

How to prevent attic black mold #7

Furnaces and water heaters installed in attic areas should be contained inside a separate and insulated room – code requirement in some jurisdictions. Any vent pipes discharging exhaust gases from the furnace, water heater, fireplace, and passing through the attic area must be double wall / B vent type or sometimes triple wall (manufacturer or local requirement in some jurisdictions).

How to prevent attic black mold #8

Missing, deteriorated insulation on attic installed air ductAttic mold - uninsulated forced air heating system ducts waste energy and release heat into the atticHeating ducts – insulate their surface to help your heating and air conditioning system perform more efficiently. Besides wasting expensive energy, heat released from the air ducts surface might condensate on the roof decking surface and cause mold growth.

How to prevent attic black mold #9

Attic mold caused by leaking roof surfaceLeaking roof – fix it as soon as possible because the mold feeds on moisture, and in this case will grow at any temperature.

And the number 10

I’m listing it as a last item, but it is actually the most important thing that causes attic black mold growth – lack of proper attic ventilation. Make sure that your attic has it and that it is properly balanced. It means that you should have a sufficient amount of attic ventilation ports split 50/50 between the upper and lower portion of the roof.

The above standard might work if everything else is perfect, but in reality, the attic vents will eventually become clogged with lint, insulation, bird nests, etc. When that happens, any combination of the first 9 items from my list increases chances for mold in your attic.

I hope that the above 10 paragraphs will help you to stop or prevent attic black mold from growing. I also highly recommend to check  my other attic black mold concerning posts for more valuable information on this subject.

You might also like

Comments are closed.