6 Tips for Healthy Below-Grade Spaces

The trick to healthy below-grade spaces is keeping the area dry and free from mold—or anything that may be a food source for mold.

Jeffrey C. May, owner, of May Indoor Air Investigations, LLC., in Tyngboro, MA, agrees with the EPA and the Basement Health Association of how to keep a safe, dry and healthy basement.  He outlined tips for keeping healthy below-grade spaces that coincide with the practices of basement health pros.

Dehumidify your basement

May says high humidity is the leading cause of mold growth in the basement.  Mold and mildew flourish when the relative humidity level is above 80%; therefore all basements—finished or unfinished—should be kept at or below 50% relative humidity. In order to maintain that humidity level, May suggests using a dehumidifier and measure the humidity level often.  He says the humidity level should be measured independent of the dehumidifier.  He suggests using a thermo-hygrometer such as Humidity Alert from Therma-Stor.com/.

A basement exhaust is not a dehumidifier

Sucking the air out of the basement will not maintain the proper humidity levels in the basement. When you pull air out of a basement, it pulls make-up air in either through the exterior or from the upper levels of the house. On a hot and humid day, the air from the house and the outside air will have a high moisture content thus introducing more moisture into the basement through the make-up air.

Keep a finished basement warm in the heating season

Simply put, when air cools, its relative humidity levels increases. The best way to maintain a 50% relative humidity level in your basement is to keep it warm in the heating season.  Most people are prone to turning down the heat in the basement if they are not using it. However, when the air is warming and cooling the air will actually create more moisture that may lead to mold and mildew growth.  May suggests keeping the basement consistently warm at least at 58 to 60 degrees F in the heating season.

Get rid of basement carpeting

There are inherent problems with carpet in the basement.  Carpet captures biodegradable dust and can be a breeding ground for mold.  While a basement should be treated like part of the house, it is not the same as the upper levels of the house.  There are different issues that happen in the basement environment and the same building principles don’t apply the same below-grade.  May recommends tile or vinyl flooring instead of carpet to eliminate the potential problems.

No fiberglass insulation in the crawlspace

Fiberglass insulation doesn’t work very well below-grade.  It is

In an unfinished basement, store belongings properly

A common scene in an unfinished basement is a bunch of cardboard boxes full of seasonal decorations and keepsakes sitting directly on the concrete floor.  Anything biodegradable on the porous concrete floor may lead to mold problems. If there is ever water or moisture problems in the basement these boxes should be off the floor on a metal or plastic shelf.  The shelving should also be at least 18 inches away from the foundation wall and 6 inches off the floor.  If you have to keep cardboard boxes on the floor, May suggests putting down a foil-laminated sheet of polyisocyanurate foam insulation on the floor and up against the wall to protect the boxes from the concrete slab and foundation wall.

19 thoughts on “6 Tips for Healthy Below-Grade Spaces

  1. 50% seems aggressive. Especially if you have a sump pump. 60 % seems better and will lead to less energy consumption with the dehumidifier.

  2. If you are using your basement as living space then you would surely want it to stay warm so that your guests never feel unwelcome in your home. Wall insulation can be internal and external. The interior wall insulation would keep cold wave out & hot air in, keeping the space warm all through enhancing all round thermal performance for the basement.

  3. In my basement, raising the relative humidity from 44% to 51% lowered the cost of running the dehumidifier from $55 to $25 per month. I used a power meter to record the kWh per day.

  4. 51% in not a comfortable level. 50-51% RH in the location where the dehumidifier is measuring means that RH will be higher than that elsewhere in the basement (encouraging mold growth), because most common 40-70 pint consumer grade machines do not move nearly enough air to condition the entire space. Dehumidifying to 43-45% RH will condition a space to similar quality as an above grade space, and ensures that you will be below 50% in all spaces of the basement.

    The typical fan speed settings of standard domestic machines: Lo-Med-Hi tell you nothing about the true CFM capacity of the system. Furthermore, they typically consume far more than the typical 6.4 amperes of a high quality dehumidifier.

    As one example, a therma-stor product moves approx 300cfm, and uses a pleated 2-inch thick filter that removes all air-born dust, keeping the internal condenser panels clean and operating at full efficiency that exceeds energy-star ratings. The savings in energy costs justify a higher cost, the quality of the build ensures a longer than typical life. Buy a real machine:

  5. I have a question. What type of insulation should be used in a crawl space, and what should be put down a dirt floor

  6. We bought a dehumidifier for our basement. My wife had started noticing unpleasant odors in the basement of our newly purchased house. After two days no more odors.

  7. My basement is partially finished. Vinyl flooring, panaled walls with no insulation. I run a dehumidifier , but it is very costly. And runs most of them time. It’s one that I have to manually set the hours. Would it pay to have insulation put in ? Cinder blocks about 3/4 up from the floor.

  8. Dehumidifiers really suck electricity. So I’ve been trying to find the ideal setting for mine, not too low — I use to set it at 30% but then it runs all the time. So now I”ve set the RH for 40%, and do not turn it on all the time, but maybe every other day or when I notice that my independent hygrometer reads 50% or above. We also do have Central air, but I guess the issue is that there are no air intakes in the basement for the Central so a dehumidifier is still desirable.

  9. Last summer the mold got away from us and we put a 70 pt dehumidifier in the basement and cleaned up the mold. This year the dehumidifier seems to be running constantly trying to reach 50%RH.
    The basement is roughly 1700 sq ft. Is there anything else we can do?

  10. We just finished our basement in August. Our 1 dehumidifier used to keep the entire unfinished basement at 50% while only running part of the day. Since we finished 3/4 of the basement and adding a dehumidifier to each side (finished and unfinished) the finished side is running constantly and yet not able to get down to the 50%. Why would this be and how can we fix this issue?!

  11. I solved my basement humidity problem. We live in a town without any rivers or creeks but we had a one hundred year rainstorm that dropped two feet of water in four block area and sewers could not take the load. My basement was one of many that flooded that day. I had to replace everything so I started by waterproofing the walls with the best waterproofing agent I could buy at the time. New rubber stuff is even better. But I have cinder block walls (old house) and I new the cinder blocks tend to accumulate water. So drilled holes in the bottom cinder blocks where the openings in the center of the blocks are and water ran out of about half of the blocks. By the way my water table is 8 inches below the concrete and my sump pumps run every day all year round. Now that I knew for sure that water was going to constantly be coming through the cinder blocks I had a choice of digging up around the house or something else. I tried something else. I found some L shaped plastic moulding and a construction adhesive that would work in water and hold the L shaped plastic against the floor and tight to the wall where I had drilled holes to let the water out. I also took by level to see which way the water wanted to run and drilled four inch holes in the concrete to allow the water to run into the gravel below the concrete. I ended up drilling about six four inch holes along the wall and three in the basement floor to be sure that low spots all had a place for water to go. Next I bought 1 1/2 inch foam board vapor barrier on both sides and glued it to the wall and floors and taped it all with the RED tape that takes your skin off. Next I put up 2×6 studs along the outside wall and insulated with Rock Wool (rock wool is spun slag so it will not burn). Then I put down a layer or chip board and a layer of plywood (no floor studs). I drilled through to the concrete and put 4 inch concrete screws every 16 inches following the lines on the plywood. I vapor barriered the rockwool and put up my drywall. I then put in my partitions and cut into the overhead cold air duct and brought it down between the studs. I leave my furnace fan on constant run all year round this spreads heat and cold more effectively and draws cold air off the basement floor to be circulated in the upper floor. After I put the plywood down and drywall was up I got a deal on some discontinued green ceramic tile. We liked it so I took the whole palette at 29 cents a tile. I tiled the whole basement and the downstairs bathroom I put in. I was 69 when I did this and now I am 77 and we have not had a single problem. We did one other thing not everyone can afford though. We live in a village and the power goes off in major storms now in the past that meant I had to get out my generator and run around with long extension cords to keep my four sump pumps working. In the sump hole I have a submersible and a pedestal back up. The submersible is a 25 gallon per minute and just keeps up when it is pouring rain. At the garage side of the house I have another submersible and one at the bottom of the stairs where pressure on the concrete stairs seeps water in the downpours. Two years ago we installed a whole house generator GENERAC 17kw great machine. I use natural gas and hooked it all up my self accept the electrical. Now we can travel and not have to worry about storms. Never a leak and no dampness at all. For those who do not know about keeping your furnace fan running you will save heat and air conditioning if you leave it run. If you happen to have a DC motor on your furnace like I do it only cost a few dollars a month to run it. By the way I used only half that pallet of green tile for the whole basement and then sold the rest for what I paid for the pallet.

  12. Before finishing a (below grade) basement with cement or block walls,, paint the walls with a water barrier like Dry-Lock

  13. I have a whole house humidifier in my basement. It was running all the time to maintain 50%. I applied foam insulation to my joist rims. Now the system runs about 30% of the time and the RH is showing 45%. You might try that to see if it helps with humidity control.

  14. Make sure that water drains away from the house!!!! If your sump pump and dehumidifier are running all the time you have water surrounding your basement. This leads to high basement humidity. Check for clogged downspouts, gutters, poor grading near the foundation, crack in the floor where water can Perculate up through. Also downspouts that do not take the water far enough from the foundation.

  15. I live on the East Coast ( high water table) have high humidity in my basement and have an independent hygrometer to help keep track of the humidity. No water in the basement ever! Recently my Santa Fe Classic died, mold grew and now we are into a 16K remediation of the basement. My problem is this; do we take down all the wall board, have all the walls painted with a mold retardation product or a rubber type of product. We do have baseboard heating in the basement that helps to keep the humidity at bay when the weather is warrents heat. Also what is the best dehumidifier on the market? I am scared to buy another Classic because if it dies I am in big trouble with the mold and the costs!!! Any advice?

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