Smart Inspector Science - The Painter Made It Rain!

By Tom Feiza, Mr. Fix-It, Inc,

I had inspected a home near Milwaukee in the summer about 10 years ago. My client called recently, clearly upset. “We’re having some painting done in the rear bedroom. I’m sure the ceiling was dry when the painter started. He claims it got wet while he was painting. I’ve talked to insulation and roofing contractors about this, but they’re no help. I don’t know who else to call. Contractors always try to sell me something!”

I talked the owner through a series of questions and tried to calm her down. It sounded like an unusual case of leaks, or condensation, or both that had nothing to do with the condition of the home when I’d inspected this property (photo: Exterior of Home).

Exterior of Home

A first look at the problem

Naturally, leaks or water intrusion with no logical explanation make homeowners uneasy. I checked my old report – it was a well-maintained mid-century ranch – and talked with the owner in greater depth about what was going on.

As the painter had finished applying latex paint to the walls and ceiling, water and paint began dripping in two places where the ceiling met the exterior wall. It wasn’t raining that day, nor had it rained in the past few days. In fact, the home never had leaks related to rain.

Our autumn weather that year had been quite damp, even foggy. As usual, evenings were cooler.

The home’s roof and gutters were relatively new, and 17 inches of fiberglass insulation was added in the attic a few years previously. Windows were recently replaced with vinyl sash / thermally insulated glass,  and the homeowner said they’d had no condensation on the glass, or anywhere else in the home, for that matter.

This sounded to me like condensation on a cool surface. (One of many free articles at my website,, discusses window condensation problems.) I told the homeowner to run a fan in the room and turn on the furnace to a reasonable 72-degree setting. Also, I said it might help to open the windows whenever the outdoor air was dry. I assured her she could call me if the problem continued.

The second visit – an in-depth examination

When the homeowner called again, her household was still off-kilter. The painting wasn’t finished because condensation still occurred at times. The family’s plans to go up north during deer-hunting season were on hold. They needed an answer so they could finish painting and put the house back together.

We scheduled an early morning visit. I wanted to catch the home when the outdoor temperature was below 30 degrees. But we continued to have an unseasonably warm fall, and when I visited the second time, the overnight low had been about 50 degrees.

Checking exterior walls

The exterior of the small ranch home was well maintained. The wide overhangs had aluminum trim and vented soffits. The “leaks” were occurring near the vents in the soffits (photo: Vents in Overhang). The roof looked fine, with no roof penetrations or flashing issues above the areas of the leaks.

Vents in overhangs

The home had recently undergone an energy audit, blower door test and infrared camera inspection. Following the audit recommendations, the homeowners had cellulose insulation blown into all exterior wall cavities. We discussed the newer windows and the recently insulated attic. They were really tightening up their home.

About 10 years previously, their old 60% naturally drafted furnace was replaced with a 90%+ furnace that vented through two plastic pipes.

I observed small water spots on the ceiling of the bedroom near the exterior wall. The owner told me  water was dripping along the outside wall, ruining the fresh paint before it could dry. There were no leaks when I was there (photo – Water Spots on Ceiling).

Water spots on ceiling

I measured the interior relative humidity (RH) at 47% to 51% in the kitchen and 55% to 57% in the problem bedroom. The interior temperature was about 65 degrees F. I always test with three electronic meters, and each one gives a little different RH reading. (I gave up on my sling psychrometer years ago because it took too much time to get an RH reading, but this is an impressive tool to use.)

The problem walls, ceilings and visible stains tested dry with a moisture meter. The edges of the exterior walls and the stained areas measured 61 to 64 degrees F. The exterior temperature was about 50 degrees F and 50% relative humidity.

Using a Wohler brand IR Hygrotemp 24, I determined that the problem wall areas were just 10 degrees F above the dew point temperature. The Wohler meter reads relative humidity, dew point temperature, and surface temperature, and then determines the temperature difference between the dew point and the surface temperature. Other manufacturers, including Protimeter, offer similar instruments.

The owner set the interior temperature at 63 degrees while away at work and 68 degrees while at home. The owner loved to open windows to ventilate the home, even when the outdoors was humid and the temperature was below 60 degrees.

Checking the attic

Throughout the attic, I saw relatively new fiberglass insulation that was about 20 inches thick – providing insulation value of about R50. There were no signs of condensation, and the attic was well ventilated with soffit and roof vents.

Air baffles were in place to keep ventilation airflow above the insulation. With the lights off, it was easy to see light in the soffits through the air baffles (photo: White and Blue Air Baffles and Insulation).

White and blue air baffels and insulation

The white air baffles were correctly installed against the roof deck, allowing ventilation air to flow past the insulation (photo: White Air Baffle Gap).

White air baffel gap

The blue air baffles looked a little strange. They were stapled on the lower edge of the roof joists, creating a large space for ventilation air. In fact, two blue air baffles (double-wide) were stapled to the rafters (photo: Blue Air Baffle Large Gap).

Blue air baffle large gap

Spare blue baffles were stored in the attic, and it appeared they should have been split in two and installed tight to the roof deck, not on the lower edge of the roof rafters (photo: Spare Blue Air Baffles).

Spare blue air baffels

Thinking it through

I narrowed everything down to the relevant facts:

  • The homeowners had significantly tightened up their home with new windows, attic insulation, and insulation blown into the wall. The mid-century home no longer leaked leak air and moisture to the outdoors as it did before the improvements.
  • The 90% furnace no longer vents and dries the home. A naturally drafted furnace vents air up the chimney 24/7.
  • The incorrectly installed blue baffles had created a great space for ventilation air but also limited insulation at the edge of the ceiling to about a 2-inch depth. Cool exterior air was flowing past and possibly into this thin insulation.
  • The painter and his latex paint added about 2 gallons of water to the room’s air within a few hours.
  • The owner kept the home at 63 degrees much of the time, which meant that wall and ceiling surfaces were cool. The ceiling dipped below the dew point temperature as the paint added moisture to the air.

Conclusion: “leak” caused by condensation

The low interior temperature of 63 degrees allowed exterior wall surfaces to cool. Because the blue baffles were installed incorrectly, there wasn’t enough insulation along the exterior wall.

Increased air flow and lower exterior temperatures cooled the outer edge of the drywall ceiling.

Once the homeowners took measures to decrease air movement in and out of the house, indoor humidity greatly increased. The newly applied paint added even more moisture to the bedroom air and raised the air’s dew point temperature.

Autumn brought cooler temperatures, so that the drywall’s temperature dropped below the interior dew point temperature. Water condensed only on the coolest area of drywall in the bedroom, where water in the paint caused condensation. The rest of the drywall and windows were still above the dew point temperature.

Here’s the fix

Remove the air baffles with a very large gap and place the baffles on the roof deck. Thicken the insulation below the baffles to the ceiling. The best step would be to use closed-cell expanding foam from the lower edge of the baffle to the ceiling; this would stop air movement into the insulation and provide excellent insulation value.

Remember, when you see water stains or even water droplets forming on a surface, think about the dew point. Always remember that if water is condensing on a surface, the surface temperature must be below the dew point temperature. And then go from there.


 Weather Tight Corporation

Like this information? Catch Tom Feiza’s new presentation on dew point and moisture science at an ASHI meeting near you.

Tom Feiza has been a professional home inspector since 1992 and has a degree in engineering. Through, he provides high-quality marketing materials that help professional home inspectors boost their business. Copyright © 2017 by Tom Feiza, Mr. Fix-It, Inc. Reproduced with permission.

Visit ( for more information about building science, books, articles, marketing, and illustrations for home inspectors. E-mail Tom ( with questions and comments, or phone (262) 303-4884

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