John Maher:  Hi, I’m John Maher, and I’m here today with Robert Weitz of RTK Environmental, an environmental testing and consulting firm. Robert is a certified microbial investigator, and today we’ll be talking about winter mold problems in the home.

Welcome, Robert.

Robert Weitz:  Thank you, John.

Ice Dams, Winter Storms, and Mold

John:  Robert, are there specific issues or situations that arise in the winter months that tend to cause mold problems in the house?

Robert:  Yes, John. Winter is a very different time of year, and when we have very cold temperatures and snow cover in so many areas, all different types of issues can come up associated with moisture and with water intrusion that can create mold, and certainly lead to a problem in that respect.

Several of the things that we look at—one of the primary things are called ice dams. An ice dam is an interesting thing in that it’s—a lot of people don’t really even know how it occurs, and they don’t know that it’s occurring until they start to see water staining on the ceiling around exterior walls.

Basically, an ice dam is when you have snow cover on the roof, people always look at it and think how pretty it is, but what’s happening there, especially in a heavy snow cover, during the day when it’s warmer outside, the snow will melt to some degree. Then that water goes down to the roof itself and it goes down the roof and it goes into the gutter.

The gutter will function to a certain point until the gutter starts to freeze. The water inside that gutter, the more there is, it will freeze. It will freeze so that the gutter becomes completely clogged. Then as that water continues to come down to the gutter, it has no place to go, so it backs up under the shingles. That’s what an ice dam is.

The water has no place to go, so it goes up under the shingles, and then it gets down onto the plywood that’s underneath, typically, and it goes through. That’s when it will penetrate down into the ceiling of the dwelling.

What’s happening is, certainly water is coming in and we know water, condensation, any high humidity level is going to normally cause mold to grow. Even though you may only see a water stain visible on the ceiling in the room, on the other side of that ceiling, there’s very likely mold growing. That mold, even though it’s not visible, could be putting spores into the air which could become a health issue and certainly be something that would need to be taken care of.

To eliminate the ice dam is certainly important to do. The way to avoid it is when we do get snow would be to pull that snow down. There are snow rakes, they’re called, and different ways that you can get that snow at the edge of the eaves down off the roof, and that helps ice dams from forming.

That’s it, that’s ice dams.

Another very common thing in the wintertime would be a roof leak. Different types of roofs have different faults that can occur and that can allow water to back up and to just go in through the roof, either down at the eave, through an ice dam, or up higher in the roof. It might be in the ridge, it might be through a breech in the roof, a broken shingle, or any one of a number of defects in the roof that could allow water to enter.

John:  Winter storms might cause something like that, too. Maybe a winter storm could cause a shingle to come loose on the roof, and cause a place where water could get in.

Robert:  Absolutely. In a blizzard condition or in a high wind condition, those shingles on a normal roof in this area, they’re asphalt shingles. They become very brittle in the wintertime as the temperature is very cold and they are blown off the roof very easily. At the beginning of a storm, particularly, the wind blows the shingle off, the snow covers the roof and then as it melts, it will go inside and it will grow mold in a very short period of time.

Humidifiers and Condensation

John:  Are there any other issues or things that happen in the winter that might cause mold to grow?

Robert:  Sure, also, because people heat their houses, obviously, in the winter, and it’s very cold on the outside, that cold on the outside and the heat on the inside, many people will see condensation form on their windows.

The windows will drip down that water, which is what condensation is, not only down onto the windowsill and the well, but sometimes, if it’s enough, it will also go down onto the floor. All of these areas can then begin to grow mold in again 24 to 48 hours. Mold spores land on a surface and they can start to propagate on that surface in that very short period of time.

John:  I would imagine, also, that just having your windows closed during the winter means that you’re getting less ventilation in your home. In a normal situation where, if you did have some moisture on a wall or some place like that in your home during the summer, but you had the windows open, it might dry out quicker and not get mold growth, whereas, in the winter, with the windows closed, you don’t have as much air circulation and that might allow the mold to grow a little faster.

Robert:  Absolutely, yes. Having those windows closed, as you say, the lack of ventilation, very key factors.

What we see a lot, as well, is a lot of children, particularly, have different respiratory issues, particularly in the winter when the humidity levels are very, very low. They can be sometimes 15 or 20 percent, which is a very low humidity level. It makes your throat dry and it dries you out inside. What a lot of families do is they run humidifiers, which introduces moisture into the air, to try to alleviate some of these conditions.

I’ve walked into some homes before where parents will run this 24/7. There’s such an accumulation of condensation that’s formed, particularly on the ceiling of a bedroom, and it’s growing mold and they keep this humidifier going until they notice it.

You can have a really good growth of mold up on that ceiling just from using a humidifier, or from not cleaning the humidifier often enough. Humidifiers have to be cleaned on a regular basis. If they’re not, the mold spores will actually gather right in and on that humidifier, so the good that you’re trying to do by putting moisture into the air is almost eliminated by the mold spores that you’re generating and putting into the air right with that added humidity.

Prevent Winter Mold Problems in the Home

John:  Right. You mentioned using a snow rake to take some of the snow off of your roof as being one thing that you can do to help prevent ice dams, and then, therefore, mold from growing because of the ice dams. Are there other things that I can do during the winter months to prevent mold from growing in my home?

Robert:  Absolutely. Sometimes we see, as well as the roofs, which certainly we want to keep an eye on year round, because it’s a maintenance issue. We want to make sure that our roof stays in good, intact condition and that it doesn’t have any areas of defect that could cause leaks.

If we get heavy enough snow, which we do very often in our area, that can accumulate certainly around the dwelling right up next to the foundation. That in and of itself, is not a tremendous issue until it starts to melt. If you have a foot or two feet or more of snow around your house and around the perimeter of the foundation, when we start to get those first few really warm days, that snow will melt very quickly.

When we have those accumulations of snow, it’s a good idea to shovel or snow blow that snow away from the foundation, so that as it melts, it won’t seep through to the foundation into a lower level and create mold to grow down there.

We certainly have a maintenance issue in that respect, as well as the roof. We want to make sure that all our windows and doors are caulked properly so that water can’t penetrate through there, and that would potentially grow mold inside of the wall cavities.

A lot of this is just maintenance and making sure you keep your house in good condition to prevent water, melting snow, melting ice from entering the dwelling and causing mold to grow.

Mold Inspections in Winter

John:  OK. Should I get a mold inspection in my house before, during, or after the winter? Or is it just a matter of getting an inspection done if I see or I suspect mold of being present or after things happen like storms or after I notice water damage from an ice dam or that sort of thing?

Robert:  Well, certainly, if we see visible mold, that’s obviously a time to get a mold inspection done. We want to know what we have, what we’re dealing with. Is it toxic? Is it an allergen?

Certainly, when we see mold, but also when we see water staining. Some people will say, ‘well, I don’t see mold, I just see the staining of water on the ceiling.’ As I mentioned earlier, you may just see staining on what you can visually see, but there may very well be mold growth behind there. So even if you just have water staining, it’s important to get an inspection done at that point.

As far as before, during, and after the winter, that’s more an issue of, what a lot of our clients do is they will get periodic mold inspections. When we go in the first time, whatever reason that we may meet someone and we do an initial mold inspection, either it’s because they have mold or they just want to prevent mold because of health issues. A lot of people have asthma, and mold can really exacerbate an asthma condition very much.

Mold can also cause asthma. Its now been documented. By preventative testing, many of our clients will do testing every 6 months or every 12 months. That can help to prevent any of these excessive mold spore conditions from developing that would be detrimental to anyone’s health as well as someone who may already be affected by respiratory conditions.

Mold Inspectors and Preventing Mold

John:  Will a mold inspector recommend changes to my home to prevent future mold problems? I’m thinking of things like perhaps putting insulation in an attic to help prevent ice dams or things like that. Would a mold inspector kind of go down that road of helping me to make recommendations on changes I can make?

Robert:  Only one that is knowledgeable. There are a lot of different types of “inspectors” in this industry. Because the industry is not regulated, there’s no licensing currently in most of the states in this country. You have to get one who is qualified.

At our company, our mold inspectors are all certified microbial investigators. It’s a tremendous amount of training and knowledge in the field. Someone like our inspectors, of course—we’re going to tell people how to prevent mold.

Our website,, has a lot of different things that can be done in blog posts and in other pages of the site that help people to prevent water, to prevent mold from occurring so that they don’t need to have a mold remediation. There are a lot of recommendations that a good inspector, like at RTK, will give to a client in order to prevent and help prevent water and help prevent mold from growing in the future.

John:  Great, well, Robert Weitz, thanks very much for speaking with me today.

Robert:  Thank you for having me, John.

John:  For more information, you can visit the website at or call 1‑800‑392‑6468.

Past exposure to lead may be to blame for over 400,000 deaths in the United States every year (The Lancet Public Health.)

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