Dark Lines on Interior Walls

Dark Lines on Interior Walls Caused by Condensation and Dust Particles

By Mark J. Donovan

Dark lines forming on the interior walls or ceiling of your home is a phenomenon associated with condensation forming inside the home. The dark lines form due to a combination of outside cold air temperatures and dust particles within the home.

Unfortunately wall studs or framing studs are good conductors of cold temperatures. When the outside air temperature is cold, the wall studs transfer this cold to the inside walls.

If, for example you were to measure the inside wall temperature of your home using thermocouples you wood see a marked difference between the temperature of the wall near the wall stud versus in the area between the wall studs where there is fiberglass insulation.

Because of this cold surface area on the inside wall and the warm moist air within the home, condensation forms over the inside wall surface where the wall stud sits behind. This condensation translates into extremely small water droplets forming on the inside walls along the lines of the wall studs. This moist surface area enables airborne dust particles within the home to stick to the surface of the inside wall along the wall stud lines. Over time dark lines will begin to become visible.

Also, if you have a cathedral ceiling in your home, it is not uncommon for the dark lines to form there as well, particularly where the ceiling meets the walls. This is due to the fact that there is little to no spacing between the roof rafter and the top wall plate of the wall with a cathedral ceiling. The cold air temperatures permeate through the roof rafter to the inside ceiling surface. As is the case with the inside walls, dark lines on the ceiling form near the wall edges.

To eliminate the dark lines, you can try washing, but in the end a new paint job is usually required. To best way to eliminate the formation of dark lines is to prevent them from forming in the first place. To do this, you should reduce the moisture level within the home during the cold seasons by using a dehumidifier. In addition, make sure you regularly change the air filters in your heating system if you have a hot air system. Blowing dirty air throughout the home is not only bad for your walls, but also your health.

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