 This is Ken Hellevang, agricultural engineer with the NDSU Extension Service, and we're looking at a series of clips on cleaning a flooded house. And this is the final of five video clips in the series, and this one is on drying the structure. It's very important that we focus on drying the structure because that's what's going to prevent any mold growth in the future. And mold growth, as we found in the earlier presentations, is indeed a health hazard, and we don't want that mold in our home, or it'll start causing us respiratory problems in the future. So the structural drying is a critical step in the cleanup process. For structural drying to occur, we need to open all of the enclosed areas. So we're talking opening the walls, if we have the floor, even if it's a vinyl and we got water underneath, we need to open them up so that we can dry. And this drying may take just several days, or it may take weeks. It'll depend on the drying conditions, how much airflow that we have going through the structure. Shown here are two different pictures of homes that are in the drying process. And I wanted to just show the house on the left there. You can see the white discoloration that is on the brick-facing. And that's because moisture is coming through the concrete. We have this effervescence of moisture that comes through. And as I indicated in the earlier slide, it's critical that we make sure that the weep holes are open so that the water drains out. And then we need airflow both on the inside of the structure and on the outside to facilitate that drying. On the picture on the right, that moisture is showing up as a darkened color. And again, it's indicating moisture is coming from the structure. And if you look closely, you can even see that there's moisture inside the house. And there'll be condensation issues on the windows if we're not getting that moisture removed from the home. And if we don't keep the humidity level low enough, that's going to lead to mold growth for certain and probably structural deterioration as well. The drying process really involves circulating air across those surfaces. We need to get them opened up. We need to get airflow blowing against that surface to aid in the drying process. And then we need to make sure that the air that we're moving across the structure is dry air. And the way that we do that is to bring outside air in that's dry and it picks up moisture from within the house and then we exhaust that to the outdoors. And what we recommend is that you put a fan in the window facing out again so that we're drawing the air into the house and blowing the air to the outdoors. To get a good suction created within the house, we need to put some kind of sheeting or whatever around the fan and close the fan so that we make sure that we're able to create a vacuum. And we'll want to move a lot of this air through the house to help with the drying process. Frequently people will ask about using dehumidifiers. Should I be running a dehumidifier rather than opening up the house? And I really recommend initially that we ventilate, we use fans and we bring outdoor air through. And that's important because we can remove gallons of water a day with moving outdoor air through the house. Where most of our home dehumidifiers are going to be taking out pints of water per day. And so once we start getting the structure dry down, then we can go to using dehumidifiers. But initially what we're going to want to do is to be using a lot of outdoor air moving by to dry the structure. I really encourage people to be measuring the relative humidity to know how we're progressing with the drying process. And humidity gauges are available both in a digital format as well as the mechanical types. Regardless of which one you're using, I recommend that we calibrate it to make sure that it's giving us accurate readings. And the best way to do that is to take a cup, put a quarter cup of salt in there, a half a cup of water into that cup, put it into a plastic bag like a gallon ziplock bag, put the cup and the meter in there, seal it up and let it sit for 12 hours. After that 12 hour period, we would expect the relative humidity within the bag to be about 75% assuming room temperature. And so that'll give us an indication of whether the meter is giving us an accurate reading or not. And then we can probably modify the reading to give us an accurate reading. And what we want to do is to measure the humidity in the house. Since moles will grow at humidity levels exceeding about 70%, our goal should be to keep the humidity level in the home in the structure under 70%. Moving a lot of airflow through to keep that drying process going and keeping the humidity level under 70% during that drying process. Particularly as we start getting later into fall and into cooler temperatures or into spring, if we're looking at spring flooding, we can enhance the moisture holding capacity by adding heat to the air. But it's important that we do both warm the air and move the air or exchange the air that's within the house. The other thing to keep in mind is that the warmer it is, the more rapid mold will grow. And so there's a little bit of a balancing act. And generally what we look at is keeping the air temperature in the home or in the structure under about 72 degrees. That's warm enough that we get good evaporation occurring, good drying occurring. But we're not so warm that we're really enhancing the mold growth. But we need both the warmth and exchange in the air. If we don't have the windows open to bring dry outside air in, we're just going to create a sauna. We're going to have warm, moist air in the house and not accomplish drying. And so we need to still, at least periodically, be opening the windows, getting the air exchange, as well as having the warmth to help enhance the evaporation. We need to continue drying until the moisture or the content of the wood is low enough that we're not going to have mold growth. And typically what we're looking at with mold growth, again, is moisture contents of the wood exceeding about 15%. So our goal should always be to get the moisture content of the wood below 15% as quick as we can. And also we can't be enclosing any walls or doing any reconstruction until we're below that 15% moisture content. And what we have on the slide here shows that if we're at 70% humidity at roughly room temperature, that puts us at just under 15% moisture. And so you'll see different numbers. Some will say we need to be down to 13% moisture to assure that we're not going to have any mold growth. And that is going to be safer, but certainly we need to be under 15%. The only way that we're going to know when the moisture content is low enough is to use a moisture meter. Actually check the moisture content of the wood, check the moisture content of materials. There are a couple of different kinds of meters. Some of them actually have little pins on the end that you push into the wood and measure the moisture content or the material. Others have some pads on the back and you just set it on the surface and it will measure the moisture content that way. But it's important that either you check the moisture content or have someone else check the moisture content before you do any rebuilding. Make sure that the wood is dry. The NDSU Extension Service has moisture meters available in our county extension offices that you can check out and use to check the moisture content. Many of the contractors and other places will also have meters. But look to make sure that you're getting an accurate moisture reading. Verify what the accuracy of that meter is that you're using to assure that that moisture content is low enough for safe rebuilding. The saturated soils will take a long time to dry out. And so we can very quickly dry out the main floor, the structural wood. But when we start talking about basements, it's going to take a long time for the moisture that's within the soil to dry out. And that moisture will be moving into the basement. It may initially come in as shown in this picture in liquid form, but more frequently it's going to be in a vapor form. And so it will look dry, but there may actually be gallons of water per day coming through the concrete, which is fairly porous to vapor. And it'll come through in that vapor form and add to the moisture load in the home. And so we need to be concerned about keeping the ventilation going, not only to dry the materials, but to handle the moisture load that will be coming in through the basement. One of the things that we recommend to really determine if the moisture is still coming through is to just take a piece of clear plastic. Maybe a couple, two or three feet on a side, tape it to the floor, tape it to the wall. Make sure that it's taped tightly to that surface. Let it sit there for a day or a couple days and look to see if moisture accumulates on the backside. It may actually show up as condensation on the plastic. It may show up as a discoloration or darkening of the concrete, but look to see if that moisture vapor is still coming through. And that'll give us an indication of the amount of moisture that's coming through and whether it's going to be safe to start rebuilding. And frequently we're looking at this dry down process in the basement of taking months. And so even though the main floor we can dry and probably rebuild fairly quickly in the basement, rebuilding really needs to be delayed until we can be assured that there's no moisture coming through. Another thing that we'll frequently see after a flood event or when we have a lot of moisture in the soils is that we have this white fluffy material that shows up along cracks in the floor or maybe even just showing up on the concrete floor on the block wall as shown in these pictures. And that is not mold. What that is is a salt. There's salts within the soil and as the moisture moves through the soil it picks up the salt. As it comes through the concrete the moisture evaporates into the air and leaves the salt deposit behind. And when it typically will look like a white fluffy material and you can determine if it's a salt by putting a little bit of water on it and it'll typically dissolve. Or there's some salts where you need to put on a little bit of vinegar for it to dissolve. But most of ours just a few drops of water and you will see it disappear. And a fairly easy way to determine whether it's salt or whether it's mold growth and frequently it's going to be salt accumulation. And it really doesn't create a health hazard but is an indication of moisture coming through the soil and it will continue until that moisture around the house has dissipated and that area is all dried out. So that brings us to the end of the section on drying your home and how important it is that we do dry out the structure. This series of five video clips hopefully will help you as you look at doing the cleanup in your own home or if you're looking at having someone help you with it to know the steps that they should be going through. So this has been Ken Helving, Agricultural Engineer with the NDSU Extension Service and we have a lot of information available on our website that you can find by just doing a search for NDSU flood information.