Issue: 79    Date: January 4, 2003

Mold & Powered Attic Ventilators

WHAT? Mold and powered attic ventilators, what could one possibly have to do with the other? You might be surprised to know and to also be aware that attic powered ventilation may not be all that you have been lead to believe. 

I hate to be the one to inform a person that they have a major problem in their home, but I love it when the problem leads to good subject matter for this little publication. Just before Christmas, I had one of those experiences. A call about mold in the attic. When I arrived and observed the underside of the roof structure and sheathing it was, for the most part, covered with, what appeared to be, relatively new mold. But it didn't stop there, there were small areas of mold in the home and extensive mold in the basement.

So, what does this have to do with the attic powered ventilation? I will get to that in a minute, but before I do, lets spend a little time on the fans themselves. I will not be naive enough to act like this is something I came up with on my own. Much of this is from the research, writings and classroom training by John Tooley and Arnie Katz of Advanced Energy. You can check them out at ^{www.advancedenergy.org}. 

You probably think that a home with or adding a powered exhaust fan ventilator in the attic is a positive thing, don't you? You may have even expressed such to one or more of your clients. Well, as with many notions we have been lead to believe, it ain't necessarily so. The time is coming quickly when the attic exhaust fan or powered ventilator will be viewed as a negative not a positive feature. Man, is the world becoming more and more confusing?

Believe it or not, powered attic ventilation's original purpose was to remove moisture from the damp crawl space under the home. Sounds strange doesn't it? Homes in times past which were "ballooned framed" had lots of openings between the crawl space and attic allowing for air flow. Adding an attic ventilation fan could help dry out the crawl space by drawing moist air to the attic and outside. Over time, installing attic ventilation fans has evolved to have claims including; reducing air conditioning bills in the summer, reducing moisture problems in the winter and extending shingle life. Unfortunately it appears that these claims may reside less in reality and more in the marketing of ventilation fans. Are you surprised, don't be. 

The reality is that attic ventilation fans, "which are suspected of using more energy than they save," can also create excess moisture, structural problems, discomfort, combustion safety problems for home occupants, and yes (as you will witness shortly) MOLD. Does it make you want to go turn yours off? Why is it so readily accepted that adding an attic ventilation fan (Powered Attic Ventilator) is an improvement? Its simple, conjecture without proper research or testing. Assumptions are made, used and encouraged without testing. It sales fans, doesn't it? The reality is (you will see more clearly why in a minute): If you choose to use powered attic ventilation you must do performance testing to determine if it causes other problems.

If you want to reduce your cooling cost, seal all openings into the attic, add insulation over the ceiling (R-30 in North Carolina) and verify or add code required passive cross ventilation. If you want to reduce moisture in the attic, seal all openings to the attic, add a tight vapor bearer at the ceiling and vent the bathrooms, kitchen and dryer exhaust to the exterior. There is no evidence or research, of which I am aware, that increasing attic ventilation above code requirements increases shingle life. 

So, what may adding an attic ventilation fan accomplish? First of all, most if not all attic powered ventilation fans are oversized without addressing adequate incoming air. Where does the extra air come from? You guessed right, from the conditioned air inside of our homes through openings in the ceilings, around plumbing pipe, light fixtures, electrical wiring, duct work, attic access stairs, and panels. Not only is the air leaving through the attic, but it is being replaced with moist hot air from outside which you are now paying to cool and dehumidify. You did want to pay for cooling the attic space and half of the outdoors, didn't you? They "suck" on the house creating negative pressures which are not only pulling your conditioned air out and hot moist air in, but may be causing combustion appliances such as water heaters, fire logs and furnaces to back draft creating a potential for hazardous conditions in your home. Stop being concerned about contaminated mail, and become concerned about your attic ventilation fan, there is much better chance it may make you sick if it doesn't bankrupt you first. And you wonder why your energy bills are so high.

Code required attic ventilation levels are adequate and passive cross ventilation is the thing to use. If you want to waste your money, waste it on something that is enjoyable, take you spouse or significant other on a trip to Vegas and gamble a little. It may cost you less in the long run.

But, Chris what about the mold in the attic? Oh, I was so busy preaching on my pedestal I forgot about what brought this to mind. Don't give up yet, if you have concerns about mold you need to take the time to read this. 

The house in question had experienced two fairly recent modifications. One was the addition of an attic ventilation fan and the other was the addition of a pull down attic stair over the stair to the basement. Basically the attic ventilation fan, which had no means of make-up air was pulling the moist mold laden air from the basement and depositing the moisture and mold on the roof framing and roof sheathing. There were other issues. It will take up a little of your time, but here are some exerts from the actual report for you enlightenment and understanding. Although you now have the general idea, this will be well worth taking the time to read. Who would have "thunk" that a simple call about mold in the attic would have required such a massive response? I guess I spend too much time in continuing ed and with my nose in some book or on the Internet.

As part of this inspection the following observations were made: 

The pull down attic stair located over the basement stair, which is open to the basement below, has a heavy mold infestation on both sides. The stair appears to be a fairly recent modification. The under side of the front roof system has an extensive mold infestation. The heaviest concentration was over the attic pull down stair radiating out from that location diminishing as it moves away from this area. The infestation does not appear to be very old. An exhaust fan appears to have been added fairly recently in the right attic gable at a pre-existing vent. What appears to have been a vent in the left gable end has been bricked over. There does not appear to be any means of cross ventilation or vents allowing outside air access to the attic. The attic ventilation fan appears to be sucking on the house pulling its make-up air from the home. 

The basement is damp and also has mold, although it does not appear as extensive or as concentrated as the front attic area. The basement insulation (which is installed improperly), floor system, stored items and trash are molded. Note; insulation must have the paper vapor bearer installed against the heated space to function properly. Failure to follow this practice allows moisture to be trapped between the paper and the floor system leading to dampness and possible damage to the structure. The mold on the floor system is evidence that this is occurring. 

The tenant reported mold in some areas of the home some of which has been cleaned up. The tenant reported that there had recently been problems with the water heater which flooded the basement and that the water heater had to be replaced. A sump pump is located near the center of the basement floor and there was water in the pit. Proper operation of the sump pump was not confirmed. The rear attic area did not have adequate access and was not observed other than directing a light through the small hatch. There does not appear to be proper ventilation in the rear attic. No access was found to the crawl space below the rear addition. The grade at the rear and both sides of the home is relatively flat and does not slope adequately away from the home. There is no exhaust fan in the kitchen or the bathrooms. The inspector did not check for proper dryer venting.

Conclusions:

The inspector did not have access to historical data related to this property nor did he make any effort to attain any other than what was voluntarily offered by the owner and the tenant. Most of this conclusion is conjecture based on the inspector's observations, education and experience. 

The existence and extent of mold is clear evidence of a moisture problem in this home. Homes do not have mold problems before first having moisture problems. Solve the moisture problem and you solve the mold problem. The interesting issue with this home is that the mold in the attic appears to be a recent occurrence. Homes operate as a system, which must be in somewhat of a balance for the home to function with relative satisfaction. This home appears to have been in a relative balanced state, although there may have been a more minor issue with mold in the basement. Something has thrown this home out of balance causing the recent extensive attic mold infestation. It is this inspector's opinion that there was not one issue, but several grouped together which caused this recent occurrence. The inspector is not aware of the order of the modifications, but this is a list of the issues.

1. A front right gable attic fan was added without consideration for cross ventilation or make-up air. This fan is sucking on the home drawing its make-up air and attached moisture and mold spores from the home from every possible opening. 
2. An attic pull down access stair was added allowing for a large amount of make-up air to be sucked through the loose opening around this stair hence the concentration of mold on and over the attic stair. 
3. Because there is a door between the basement stair and the first floor of the home, most of the air being sucked into the attic is coming from the basement. 
4. The basement is damp and has mold infestation that has been made worse by the recent flooding from the water heater and improperly installed insulation below the floor system.

Other issues, which are or may be contributing to this problem, are:

1. Inadequate slope at the exterior grade, which is not directing storm water away from the home.
2. Possible lack of moisture barrier on ground in the rear crawl space floor. (No access found and not observed by this inspector.)
3. Possible lack of adequate ventilation for the rear crawl space.
4. Lack of exhaust systems in the kitchen and bathrooms.
5. Possible lack of proper ventilation for the dryer (Not observed by this inspector).

General Recommendations:

The moisture problem must be dealt with and the mold cleaned up. This home has an extensive mold infestation. Molds produce tiny spores to reproduce. Mold spores waft through the indoor and outdoor air continually. When mold spores land on a damp spot indoors, they begin growing and digesting whatever they are growing on in order to survive. There are molds that can grow on wood, paper, carpet, and foods. When excessive moisture or water accumulates indoors, mold growth will often occur, particularly if the moisture problem remains undiscovered or un-advised. There is no practical way to eliminate all mold and mold spores in the indoor environment; the way to control indoor mold growth is to control moisture.

The key to mold control is moisture control. It is important to dry water damaged areas and items within 24-48 hours to prevent mold growth. If mold is a problem, clean up the mold and get rid of the excess water or moisture. Fix leaky plumbing or other sources of water. Wash mold off hard surfaces with detergent and water, and dry completely. Absorbent materials (such as ceiling tiles & carpet) that become moldy may have to be replaced.
Potential health effects and symptoms associated with mold exposures include allergic reactions, asthma, and other respiratory complaints. It may be expedient for the occupants to vacate the home during clean up. Be aware that some of the contents of the home may be infested and need to be cleaned or disposed of. Reduce indoor humidity (to 30-60%) to decrease mold growth by: venting bathrooms, dryers, and other moisture-generating sources to the outside; using air conditioners and dehumidifiers; increasing ventilation; and using exhaust fans whenever cooking, dishwashing, and cleaning.

Specific Recommendations:

Here are specific recommendations for this home in the order of importance:

1. Disconnect the attic exhaust fan and consider removing it completely. Powered exhaust fans tend to move too much air and pull conditioned air from the home or excessive moisture laden polluted air from the outside.
2. Provide passive cross ventilation for all of the attic space. One method would be to add soffit and ridge vents. Other methods are possible. It is generally recommended that one (1) square foot of free cross vent area be provided for every one hundred and fifty (150) square feet of ceiling area.
3. Remove or clean all mold infestations throughout the home. 
4. Stop storing items in the basement, which will be effected by dampness and/or control the basement moisture.
5. Install a vapor barrier over the ground in the rear crawl space area and verify that adequate cross ventilation has been provided. One (1) square foot of free vent area should be provided for every five hundred (500) square feet of crawl space.
6. Tighten up and provide weather stripping and insulation at the pull down attic stair.

Here are additional recommendations, which should be considered:

1. Provide adequate access to the rear crawl space and attic.
2. Correct the grade around the home to slope away from the home a minimum of 6 inches in the first 10 feet.
3. Install exhaust fans in the bathrooms and over the kitchen range.
4. Verify that the dryer is properly vented to the exterior.
5. Remove the insulation in the floor over the basement.
6. Replace the insulation in the floor over the basement with properly installed insulation.

NOTIFICATION STATEMENT: MOISTURE REDUCTION IN CRAWL SPACES/BASEMENTS/ATTICS AND THE POSSIBLE EFFECT OF DRYING MAY CAUSE NOTICEABLE CHANGES AND DAMAGE TO THE BUILDING ASSEMBLIES AND COMPONENTS.

Reducing the amount of moisture accumulation in the crawl space of homes as may be recommended, as part of this report (vapor bearers, ventilation, etc.) is a sound building science practice. It will lessen wood rot and mold and its attraction to insects and the amount of moisture and odor entering the home from the crawl space. 

Drying Effects:
In some cases drying has caused problems. You should be aware that in some cases flooring, wood trim, and framing might shrink. This can cause gaps to appear where connections were swelled by moisture prior to reduction of moisture flow into the crawl space(s). There have been reports that a floor may start to creak where it was silent, and dry wall may crack. If you have concerns, simply do not proceed with the moisture reduction work.

Note: For additional information on Mold, check out my web site www.chrisdhilton.com. Look at the "Back Issues" area under "Interior" and there are three articles: Mold, Mold II and Protecting Homes From Water Damage. If you haven't read these yet, you need to. 

Addition on January 12, 2003:

Follow up on this article. Keith Rogers (a local builder) had the following response after reading this article:

To add a new house perspective on this, long-term maintenance is another reason not to use a power ventilator. To my knowledge none of the regularly available attic ventilators have replaceable motors available. In 5 years or so, when the motor burns out, what do you have to do? Tear out the fan, have a roofer replace it, and get an electrician to rewire the new one! Not to mention that the fans are usually installed near the ridge, requiring an extension ladder to be brought into the attic (pulldown steps for access?) to rewire them. 

Passive ventilation like a ridge vent, costs more on the initial installation, but has no moving parts.

I just hate those fans anyway! We stopped doing them about 8 years ago, when we had been in our own house for 5 years and our fan burned out. I got a taste of the mess I had (unwittingly) created for people! Despite some evidence to the contrary, home builders can learn from experience.

Keith is one of our exceptional local builders who honestly care about how their homes affect the people who live in them. Do you believe it; a home inspector can say something nice about a builder.

Thought for the week

Just because you have been told and may believe it to be the truth, 

doesn't mean that it is the truth. Question Everything!