One source of mold in the attic

We had a warm spell a few weeks ago and I noticed that there were some large icicles hanging off the gutter on the back of our house.  I initially thought it was maybe an area where some leaves were clogging the gutter, so the water overflowed forming the icicles.  The weird thing was that I noticed water dripping out of the soffit vent in that area.  I of course was concerned this meant that there was some flooding inside the attic area, which was then dripping out of the soffit.

So, I went into the attic to try to take a look.  We have a nicely planked attic area so I was able to get around pretty easily.  Unfortunately, the soffit vent with the leaking water was in an area I couldn’t get to.  I didn’t see any water dripping inside the attic, and I didn’t see any wet spots on the flooring in the attic.  I guess I could have tried to take a closer look and maybe move back some of the insulation in the area where that soffit vent should be, but I didn’t bother.

The one thing that did concern me was that I noticed on the north facing roof there was a thin layer of ice on the ceiling, which is the underside of the roof.  I did some reading online and but I couldn’t find a clear explanation of what I was dealing with, other than several articles talking about leaks in the ceilings going up to the attic, leading to excess humidity in the attic.

We have an attic fan that has both a thermostat and a humidistat to turn it on/off.  The humidistat was set for 75% which seemed really high to me.  The fan was not running when I was up there.  As soon as I turned the setting below 75% the fan kicked on.  I went ahead and turned it down to 40%, which is what I know we set our humidifier to be.  I wasn’t sure what a normal humidity should be in an attic, and I couldn’t find any clear answers online either.

The next day, I called a local company that specializes in attics.  I had worked with them a few years ago to fix a bathroom fan that wasn’t vented properly to the outside and also to see if they would recommend a whole house fan.  It turns out we didn’t have a good spot to locate a whole house fan, so that wasn’t an option.  When the fixed the bathroom fan ventilation, they also recommended we increase the size of our soffit vents.  We went ahead and did that at that time.

I told him the problem and his first question was what do we have our humidifier set to.  I told him 40% and he said that is probably higher than what most people need it to be.  He said during the cold weather, the best way to tell what we should set the humidifier to be was based on moisture collecting on our windows.  He said that if there is 1/8 inch of moisture on the bottom of the window, that means our humidity setting is about 10% too high.  I would guess that is about how much moisture we had, so I turned our humidifier down to 30%.  He also said that if you have 1 inch of moisture at the bottom of your windows, that means your humidifier is probably set about 20-25% too high.  I’m not sure where he got the numbers, but he’s been doing this stuff a long time, so I suspect he knows what he is talking about.

He also asked if the ice was on the North facing part of our attic ceiling.  He said that they get calls all the time for this problem during this time of the year and it is almost always on the North facing roof.

He said that the attic fan should be set to 75% humidity because if we set it any lower he said it will run all the time.  He suggested we turn the humidifier down 10% and leave the attic fan running for a few days.  He said we should then reset the attic fan to 75% so it is constantly running.

I also asked him about trying to limit excess moisture by fixing penetrations into the attic, such as around recessed lights.  He said that the amount of humidity getting into the attic that way is minimal, because insulation should reduce the airflow in those areas into the attic.  He also said that we don’t want to have the house sealed too tightly as that can cause other problems.

I asked him specifically about the pull down stairway that accesses the attic, as I had read that a lot of humidity can enter from that area, and I saw several products online that suggest they correct that and can also improve the insulation around the pull-down stairs.  He said that he recommends a product called the attic tent.   He said it is easy to install and will significantly reduce the air flow through the pull-down stairs.  I checked it out, and the product is around $199 but Amazon seemed to have it cheaper.  It got very positive reviews on Amazon except from one troll who was promoting a competing product by Battic Door.  The reviews for the Battic Door product were not as good.

I had figured I would go with the Attic Tent product.  I went into the attic to measure the dimensions as they come in different sizes.  Of course my stairs were made from neither the 4 inch or the 5 inch boards, but instead were 4.5 inches being right between the two sizes.  I was pretty sure I’d have to go with the larger size that normally fits the 5 inch boards.  I then was measuring the dimensions of the stair opening and realized that my attic floor was finished at a different height along one of the sides of the opening.  In other words, I could not easily install something to seal around my attic opening, because one side was higher than the other three.

I thought up a few options.  I could build up the other three sides with some boards, and then seal the attic tent to the boards.  I wasn’t sure how wide I’d have to make the boards to get it to seal, but I thought I could try doing that after I got the product to use it as a guide.  I wasn’t thrilled with this option as I didn’t want to have to nail anything into the floor, and then I’d also have to consider sealing the boards so that air does not escape through the cracks between the boards.  It was beginning to seem like it could become a big headache.

While looking through the different products, I also saw some comments on a product by Owens Corning to insulate the attic stairs. They were selling for $50 on amazon and had decent reviews.  One of the few negative reviews was from the same troll promoting the Battic Door product.  The other negatives seemed to have good reasoning saying that there is not necessarily a good seal between the bottom of the insulation and the attic floor.  Basically the Corning product is held down by its own weight, being a large tent shaped piece of insulation with a foil covering.  One reviewer commented that his pull-down stairs would push the tent out of the way when closing it, because of the location of the retractable arms.  My stairs are recessed enough that I wasn’t worried about that.  One big advantage of this product is that it is cheap, being only $37 at my local Home Depot.  Also, because my floor was not even on all sides, I figured that this product being flexible would be more easily able to be adjusted to the height difference.  I also figured after I got it set-up, I could use thick weather-stripping on the floor to better block the area where air would flow.

I went ahead and bought the Corning product at my local home depot for the $37.  I also bought a few rolls of 1/2 inch thick weather-stripping.  I set the insulation up in the attic and I was surprised that the base actually seems to fit pretty flush against the attic floor, except for about 3-4 inches of space near where the one side is a different height.  The gap is small, going from 1 inch high down to no gap over the 3-4 inches.  I haven’t done it yet, but I plan on using the weather-stripping to seal that area.

Unfortunately, I have no easy way to test whether this actually does anything.  I don’t expect this to make a significant enough difference in my heating or cooling costs.  I suppose when we get some more cold spells I will have to venture up into the attic and check for ice.

When I was putting the Corning attic insulation over the pull-down door, I noticed that there was no longer any ice or moisture along the attic ceiling.  I didn’t expect to find any ice because the outside temperature was over 32 degrees.  I was glad I didn’t see any moisture.

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