Ghost lines on drywall - and how a thermal camera sees them.
You've seen ghost lines, those shadowy lines on drywall. You can see them in the walls and on the ceiling.
What are they?
They have been called ghost lines, drywall shadow lines, ghosting - but it doesn't matter what you call it. Ghost lines happen.
But why? What are they?
Ghost lines can be created by a variety of things - moisture, moving air, dust, soot, and particulates inside the walls or attic. Sometimes nail or screw head spots can be seen as well.
Mostly what you see is insulation related. When there are gaps between insulation, or it is loosely applied, falls down, or otherwise becomes separated from the drywall, air gets in. This allows for a convective loop, or moving air, as it heats and cools. It's the same principle as what moves air during a thunderstorm, when the wind blows. Except inside a wall, or in an attic space, the moving air, or convective loop, is very small.
But the air still moves! Heat seeks cold, so the air is almost always moving as there is not always a temperature equilibrium anywhere. As temperatures change inside walls, ceilings, or attic spaces, air moves, and THERMAL TRANSMITTANCE happens through the drywall.
And those ghost lines appear!
Viewing the same location two different ways interesting things emerge.
The digital photo on the left clearly shows the ghost lines in the drywall. I noticed them as I walked in and knew what Mighty Mo would see.
The thermal image on the right exactly mimics the lines on the left. Except the thermal image is coupled with temperatures! The ghost lines appear as dramatically cooler areas. The coolest temperatures in the attic approach the air temperatures outdoors.
Thermal images lend a lot of information to the physics and thermal radiation that influences an indoor environment. Until the arrival of thermal cameras to the home inspection scene (which I began using 13 years ago) we did not have this kind of evidence that accompanied what we suspected.
My recommendation: thermal imaging gives a lot of definitive information about a property. The house is the house. The camera does not invent images. They are based on temperatures, and can be described with a variety of palettes to give different kinds of information. The information here is clear. Insulation is a permanent thing in a house. If it is done right, it is right forever. If it is not done right, it is not right forever. And the consequences of both of those things are forever. It pays great dividends to do insulation right the first time!
Jay Markanich Real Estate Inspections, LLC
Based in Bristow, serving all of Northern Virginia.
Office (703) 330-6388 Cell (703) 585-7560