Indoor Humidity

Why do we care about the level of humidity in our homes?

If the humidity is too high: we’ll get condensation on cool surfaces such as windows or walls. In extreme cases condensation can even occur inside of walls which could be harmful to our homes. Wood floors can cup or warp. Windows can be damaged from condensation. And we’ll just feel uncomfortable in the summer. Also very high humidity can contribute to the growth of mold.

If the humidity is too low: low humidity is generally less of a problem but can cause gaps in our floors, static electric shocks when walking on carpet, dry itchy skin, and some people can experience respiratory issues such as nose bleeds. In winter dry air feels cooler so we may need to turn our thermostats up.

dscn6023What should the humidity level be in our homes?
The ideal relative humidity should be approximately 30% to 50%. This range is our target but in the summer we’ll be satisfied with around 55% and in the winter we’ll be down around 30%, or even 20% if you’re getting condensation on your windows.

How do we know what humidity level we’re at?
I recommend that every homeowner purchase a hygrometer. These can be found at any hardware or big box store for around 10 dollars. They are accurate enough for this purpose. The one I use is made by Ambient Weather (about $40) and has wireless remote sensors so I can obtain 4 different temp/humidity readings. One outdoors and three locations inside my home.

How do we control the humidity?
Always do the easiest and least expensive procedures first. Often they will suffice.

Too much humidity:

Use the bath fan when showering and let it run for 15 minutes after. You can even install a switch that has a timer that will let the fan continue after the shower.

Make sure your dryer vent duct is sealed and vented to exterior properly (tape duct joints with foil tape) and keep duct free of lint.

Repair any plumbing leaks. That perpetual wet spot under the laundry tub that you thought was harmless because it is right by the floor drain is adding humidity to your entire house and making you’re A/C work harder! If you have sweating cold water pipes in an unfinished basement ceiling you can buy foam sleeves to insulate them and stop the dripping.If you have a home that has a crawlspace with a dirt floor it must be covered with a 6 mil poly sheet.

Using a range hood and keeping pots covered while cooking also helps.

If humidity is still too high a portable dehumidifier will help. Their limitations are that they work best in warmer temps and higher humidity. They are of limited benefit in a well ventilated area but work well in basements and can take some of the load off of your A/C.

Note: If you have wet or damp walls or floors in your basement you may have water intrusion from the exterior. This is an important issue and will be addressed in a future blog.

Humidity is too low:

Rarely on a home inspection in the Twin Cities area do I find an instance where low humidity has caused a problem with a structure. Sometimes wood floors will develop gaps but these typically close up in the summer. Low humidity has more of an effect on the occupants of the home. As a home inspector I would much rather have humidity that is too low than too high.

House plants and vases add a nice amount of humidity. If you can leave the bathroom door open when showering that can help. Still use the bath fan though! Leaving some water in your bath tub will add humidity but is not recommended if small children are present. A tea kettle on the stove is great but don’t let it run dry. Open the dishwasher door after last cycle and let the steam out. A room vaporizer can take care of a bedroom if that’s what you need. There are lots of human activities that raise the humidity level but they are band aid solutions. If your air is severely dry in the winter you probably have air leaks. This lets cold dry air in and your furnace runs harder drying the air out even more. Proper caulking, weather stripping, air sealing, proper storm doors and windows all should be addressed.

If the simple remedies aren’t your style the next step up is a whole house humidifier. When inspecting homes most of the whole house humidifiers I see are not in operation. Either the occupants have decided they are not necessary in our Minnesota climate or the humidifiers have not been maintained and have quit working. If you use a whole house humidifier the maintenance is critical! When not maintained they build up a mineral scale and quit working or worse yet they build up mold or mildew and can distribute spores throughout your home. Have them included in your recommended annual HVAC maintenance.