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From a Certified Pro
Certified Energy Auditor
Residential Comfort & Energy Efficiency
Saturday, August 15 2020
Why does Mold Form on Plywood?
Typically, condensation in the attic starts due to a moisture issue created by introducing two completely different air masses. Here are the two possible reasons this problem is happening in your attic.
1. No air sealing at the attic floor to stop warm, conditioned air from escaping into the attic (warm air/ winter issue) coupled with a lack of adequate attic ventilation creating conditions that are right for condensation that adheres to the plywood and eventually forms mold.
2. In summer, a leaking AC HVAC duct in an attic and other HVAC-related inefficiencies can allow air to seep out and interact with the hot, humid attic air, mainly if the attic is not well vented.
If you find this helpful, check out more info on my YouTube Channel @hometrustremodeling
Warm Air Exfiltration - Winter Issue
Signs that you have an attic moisture issue problem during cold months can sometimes be seen on the plywood.
Winter Problems - What to Look out For
Frozen droplets on the tips of nails and hurricane clips signify that warm, humid air is migrating from inside the home into the attic and settling in the wrong places.
But, how is the warm, humid air getting into this attic? The usual suspects...can lights and top plates!
Recessed light thermography taken at the attic floor reveals heat from inside the home escaping into the attic.
Top plates are also leaky spots if not appropriately air-sealed. Top plates in the attic will exist above the hallway, between rooms, and other areas separated by a wall.
Summer Condensation - How it Formed in This Attic
At first, when I got up in the attic, I could see the stains. It was apparent quickly that there was an issue beyond what I usually see.
I have been in many attics and seen a lot of roof sheathing over the years. I was not exactly sure about this one at first. I have not had a mold case. Overall, is is pretty rare, at least in Maryland.
At first, I considered the possible interaction of the cool conditioned air in the living space below and the warm, humid attic air. Maybe I could find a large opening or bypass where the air interacted, but why would be so high up? Then I turned around.
I saw a huge HVAC supply duct lying completely undressed and the picture was getting clearer.
Summer Moisture - 4 Things to Lookout For
Here is the recipe for mildew and mold growth on the plywood in warmer months:
1. HVAC Ducts
*Second HVAC system located in the attic or crawl space.
2. HVAC System Size
*The second HVAC system is improperly sized.
3. Poor thermostat location.
*The thermostat is located in an area reported to be a "hot spot" on the floor so the machine was running longer.
4. Poor Ventilation
*Improper baffle placement.
A baffle is supposed to act as a channel for the open soffit intake below.
The soffit opening is covered with insulation, not allowing good flow.
Here is what it is supposed to look like.
How to Remove Mold from Attic Plywood
Answer: Control the humidity and the mold growth disappears.
Here are the steps recommended to solve this issue in the long term.
1. Remove the insulation around the soffit/eave areas - the entire perimeter
2. Reinstall baffles at the eaves to promote the best possible organic attic ventilation.
3. Re-position the insulation so as not to cover the openings.
4. Seal the duct seams and tightly insulate the supply plenum (central AC duct) to eliminate leakage (lost energy) into the attic.
Written by Eric Gans
Do you have something going on around the house? Maybe my YouTube Channel can help.
YouTube Channel @hometrustremodeling
I would like to hear your comments about this article. Feel free to post something below...
Put new roof on house 4 years ago.Went in attic black staining on plywood in attic .But not the whole attic just the front of house back of house has nothing on plywood.Was wondering why it has staining front of roof none on back part ? Thanks
Posted by William riches on 12/08/2020 - 12:46 PM
Hi William, What direction does the front of the home face? Eric
Posted by Eric Gans on 12/09/2020 - 05:12 PM
Here we get to know about black mold on attic side of roof information in detail. It helps us to decide that which one is best among its types. I enjoyed reading this article and would suggest others it as well. Thank you for this article! This is really very informative for us. I must say this, if you get time can visithttp://www.insulationservices.co.nz for ideas on this topic.
Posted by Insulation Auckland on 01/25/2021 - 05:50 AM