Mildew associated with Radiant ceiling heat

[Bill Anglin]

I did an inspection today the attic has black mildew on the underside of the roof sheathing. There is a power ventilator installed through the roof but I was unable to make it respond. The homes heating system has recently been updated with a gas furnace installed in the attic. The previous and still active heating system is an electric radiant heating system installed in the ceilings. I was unable to inspect the system as it was covered with insulation. The 4 in 12 roof pitch made access difficult. I'm trying to determine the cause of the mildew. Does anyone know if radiant ceiling heat is directly associated with high humidity or mildew problems in an attic. The ventilation in the attic is being achieved by a power ventalator, soffit vents, roof vents and a ridge vent. I would think there is adequate ventilation but the mildew suggests otherwise. I know very little about radiant ceiling heat and this is the first home I've inspected that has one. Any insight on this subject would be greatly appreciated. The mildew is throughout the attic almost every inch.

[Jerry Peck]

Just curious, is that a double wide or a two-piece modular?

[Jon mackay]

Bill, this is not likely related to the heat system.
If the house was built in the 70s or 80s, it may be from over tight construction where the house can't breath well.

Were there any moisture issues in the basement?
Were the soffit areas free of insulation or blocked?

The power vent suggests that there has been ventilation problems but these often do nothing for the winter months and as a result, moisture can not escape from the attic and condensates on the sheathing which will get moldy over time..

[Stuart Brooks]

To me, the odd thing is the discoloring looks like it is only on the roof decking.
Questions: Was the roof sheathing damp? How did you determine the stain was mold? Was there any other evidence of moisture in the attic or ceilings below?

[Bill Anglin]

It's a 2 piece modular, built in 1983. I didn't test the material for moisture and my analysis of mildew is solely based on what was seen. The top portion of the sheathing is plywood and the lower half is OSB. The mildew on the OSB is more circular. I don't know if it is active or from a previous condition. No other signs of moisture in the interior.

[John Kogel]

It's a 2 piece modular, built in 1983. I didn't test the material for moisture and my analysis of mildew is solely based on what was seen. The top portion of the sheathing is plywood and the lower half is OSB. The mildew on the OSB is more circular. I don't know if it is active or from a previous condition. No other signs of moisture in the interior.I would go ahead and call it mould or mold, but that's just me. And it appears to be active, just from the pics. If it's 3 dimensional and wipes off easily, it's probably alive. :D

It's possible the soffit vents are blocked by the blown-in insulation. Multiple roof vents can sometimes short-circuit the air flow, so that no air is drawn thru the soffit vents.

Look for indoor air leaking into the attic. Possibly past the ceiling fixtures or the seam where the halves were joined? Leaking ductwork? bath fans? Attic hatch? Just a few ideas. It can get complicated, but usually, there's indoor air leaking into the attic, and insufficient venting.

[Terry Moore]

Could be some plywood sheathing that was use for concrete forms and then set outside for a while. Then later used as the decking

[John Kogel]

Could be some plywood sheathing that was use for concrete forms and then set outside for a while. Then later used as the deckingNope. It's a modular home, so they likely used clean new wood for the sheathing. Up here, it would all be built under cover as well. There's a bit of staining on the 3rd truss in the pic. There's moist air leaking into the attic, and it is not properly ventilated.

[Craig Barr]

I have seen this type of radiant heat and you can't see it from the attic. The lines are run on the inside of the sheet rock and then plaster is floated and coated over the wires or tubes. Makes the ceilings really heavy. A lot of homes in my area that were built in this time frame had the bathroom fans vented to the attic and mostly they are covered with insulation so that the air moves through the insulation. They have changed that and the newer codes require the fans to be vented out of the house but there are still thousands of homes out there that were built with the bath fans vented inside. That is where I would look.


I did an inspection today the attic has black mildew on the underside of the roof sheathing. There is a power ventilator installed through the roof but I was unable to make it respond. The homes heating system has recently been updated with a gas furnace installed in the attic. The previous and still active heating system is an electric radiant heating system installed in the ceilings. I was unable to inspect the system as it was covered with insulation. The 4 in 12 roof pitch made access difficult. I'm trying to determine the cause of the mildew. Does anyone know if radiant ceiling heat is directly associated with high humidity or mildew problems in an attic. The ventilation in the attic is being achieved by a power ventalator, soffit vents, roof vents and a ridge vent. I would think there is adequate ventilation but the mildew suggests otherwise. I know very little about radiant ceiling heat and this is the first home I've inspected that has one. Any insight on this subject would be greatly appreciated. The mildew is throughout the attic almost every inch.