Residential Comfort & Energy Efficiency

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.

Poor ventilation is trapping the air rather than allowing it to organically or mechanically be exhausted (through a ridge vent or attic fan).

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.

  
This is a close-up image taken of a recessed light. I took it from the attic during cold weather.

   
This is the same recessed light. I took a thermal image of the recessed light.

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.

Close-up of a top plate. 

Thermal image of top plate close up.

Summer Condensation - How it Formed in This Attic

This example is one I came across during the attic inspection at a home energy audit.

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. 
*The connected ductwork is also in the attic or crawl space. 
*The ducts are leaky and improperly insulated, allowing cold air to escape.

2. HVAC System Size

*The second HVAC system is improperly sized. 
*Too large for the space/square footage it is servicing. 
*The larger blower pushes cooler air through leaky ducts and into the attic.

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.
*Blocked eaves (air intake).
*No ridge vent.
*Inoperable attic fan.

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
I have over 2000 energy audits under my belt in Maryland.  I like to take my personal experiences with each of my audit customers and try to get the things that concern them out into the world so others can make sound home improvement decisions - in the correct order - according to their needs.
 

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...

Duct leakage inside a home can account for as much as 30% of energy loss.  But, how do you fix a problem that mostly lives behind walls and in hard to reach locations?

Most homeowners that have a knee wall in their home don't know they have a knee wall in their home.  This article discusses the different type of knee walls, the issues knee walls present in terms of comfort and energy efficiency and how to properly treat knee walls for peace of mind.

Common Construction Philosophies

Maryland crawl spaces can be a giant source of comfort issues in summer months.  Crawl spaces are typically intentionally connected to the outside humid air with vents around the foundation wall.  The idea was that installing vents will create ventilation.  Unfortunately, due to pressure dynamics that in many ways are related to meteorology pressure highs and lows, the air in the crawl space becomes more humid and damp and issues are compounded with the steady infiltration of stale, humid air.  If there are ducts running through a crawl space it is more important to consider what measures can be taken to treat the crawl space.  Spending a little money up front on crawl space encapsulation will save much more money in the long run if you consider duct leakage, overworking HVAC equipment and extra infiltration of warm, humid air in summer and cold, dry air in winter. 

Check out this before and after crawl space encapsulation project with blocking and sealing open vents.

Crawl Space Encapsulation Maryland - Smart Thinking
In the simplest terms, to encapsulate a crawl space is cutting it off from the outside air.  When I was young we had the Weather Channel that was just a table with today's temperature and conditions and it would cycle through each city in the U.S.  San Diego, no matter the time of year it seemed, was always 70 degrees and sunny.  We want the crawl space to be 70 degrees all year round - without the sun, of course.  By doing so, you are bringing the space into the "envelope" of your home.  If ducts exist in the crawl space, the ducts don't have to work as hard to service the rooms above. 
 

Overall, the HVAC system is asked to do less as a result of crawl space encapsulation and yet the inhabitants are more comfortable.  

Imagine if that was a formula for everything in life.  Work less and gain more!

Learn more about common sources of home comfort issues.

Hometrust Remodeling recently completed an insulation job in Laurel, MD 20723.  The project consisted of the following measures:

• Air seal the attic floor
• Install soffit baffles at eaves for ventilation
• Cut soffit holes to add air intake for attic ventilation
• Seal 4 recessed lights
• Add 10" of loose fill blown cellulose insulation
• Treat the main attic access hatch
• Treat the garage attic to encapsulate the space
• Sealed accessible HVAC duct connections

For most insulation to be effective it is important to stop the flow of air by sealing up holes and cracks in as many accessible areas as possible. 

Insulating the accessible skylight kneewalls to R13 after sealing smaller crevices/cracks and adding sheathing (air barrier) over the insulation will maximize boundary effectiveness and reduce air communication between the living space and the attic (outside).

                                 
Completed attic insulation & skylight kneewall 20723                                      Garage roof encapsulation in Laurel, MD                   

Most of the largest leaks in homes occur where framing (such as floor joists or wall studs) span from an area inside conditioned space to an unconditioned or vented space, such as the attic,crawlspace, garage, or roof. Appropriate blocking is needed in these instances.

Untreated recessed lights are invisible gateways for air to communicate between the inside (conditioned space) and outside (attic).  Covering and sealing accessible recessed lights will eliminate this issue.

Encapsulation, using open cell spray foam, was completed for this project so that the space below, including the HVAC unit in the garage attic, would become part of the overall "envelope".  The garage is going to be converted to living space (in-law suite) so by encapsulating the area above the space, it will make it easy to complete the job once the work gets done and when the space is changed, the HVAC will also benefit from being enclosed inside the house rather than outside (garage attic).

Learn about some of the benefits a homeowner can get from having an air leakage test performed by a blower door system.

I wanted to share an experience that I had when I moved into a townhouse in Laurel a few years ago. Prior to moving to North Laurel, I lived mostly in West Laurel, so I am not new to the area. What was a first time experience for me was July 2018. Whew! It was so hot! And so was the upstairs bedrooms all day and into the night and we were a bit concerned as it was our first summer in the new home and we like it cool when we sleep. At the time, I was about six months into being a home energy auditor. I was learning a lot, especially out in the field working with people in their homes all day. What I was realizing is that I am not alone. Lots of others are also hot upstairs in the summer. I wanted to share because here is what some people do and it does not solve their problem: 1. Replace HVAC System 2. Replace Windows Here is what we did (with a little insider info) and it came along with measurable results: Air sealed and insulated the attic and basement Now, the temperature throughout our townhouse is far more regulated. The upstairs is still a bit hotter during the hottest of days with full sun, but it cools down in the evenings and we can sleep. During the winter after getting the insulation work done, it was much easier to heat the house too. Anyways, I like to share that story with people I know because I see too many people trying to solve comfort with new AC or new windows and the only way to do it is with proper home assessment & correctly installed insulation. Hope you find a way to beat the Maryland summer heat!!

Key Purchasing Factors Should Be

• Energy Efficiency – cost savings, reduction of heat loss
• Price – affordability, something that fits your budget
• Style – find the windows that will work best with your home
• Security – felling safe at home
• Durability – won’t rot, deteriorate or crack
• Maintenance – easy for anyone to maintain and clean
• Durable Seals – reduces drafts for higher level of comfort
• Noise Reduction – lessens the amount of outside noises
• Appearance – enhances the beauty of your home – in/out
• Easy to Operate – open and close without any hassles
• UV Protection – guards against the sun’s damaging rays
• Ease of Installation – easy, neat and accurate

One of the keys to performing a good energy audit is to be consistent.  Consistency, yields high quality results for the homeowner. Having a sound routine and being sure to go through that routine for each and every house will serve the most seasoned home energy auditors very well.

One very nice experience as an auditor is to find things for people that are so easy to fix they could do it later in the afternoon after the audit is complete.  And, for very little money.  Each and every audit I make it a point to inquire with the homeowner about why they contacted us.  Is it because of a specific problem you are experiencing?  This helps me narrow some of my searching because it gives me good insights in to where to spend my time looking.

This leads my to a find I made at an audit Davidsonville, Maryland.  For an auditor, it is a fairly common issue, although some of the time it is more hidden and less obvious and could be missed.  On this day, the homeowner mentioned that one of the reasons they called is to figure out why the kitchen is so cold.  They moved in last summer (June) and now it is January and the experience has prompted a call to figure out what is causing the problem.
 

Front of the home.

Missing microwave/exhaust fan in the location of the outside vent hood.  The kitchen had exhaust at one time.

This is a sample of a remodeled kitchen in an older home that has a recirculating microwave above the stove.

This situation illustrates to a homeowner what the envelope of the house is, and how the thermal boundary around the envelope is so critical to comfort and efficiency.  The best way to describe the building envelope is to say that it is the separation point between the inside of the home -where you live, sleep and pay for air to be conditioned and the outside which can be described in several terms.