Mold formation in the roof at the floor ladder

Hello everyone,

we moved into our new house in 2020 and now I have discovered some mold spots upstairs in the attic. These spots are all located near the opening of the loft ladder. We have a cold roof.

This can only be related to the fact that heat (due to missing or insufficient insulation) rises upwards and condenses there because of the cold air, right? At first glance, I could not see any damaged vapor barrier. The mold or the damp spots are only visible at isolated points around the opening. Other areas are flawless and dry.

I have attached a few photos of the affected spots (spots 1 to 4). In the narrow gap at spot 1, I can see the vapor foil at the bottom. So, there is no insulation or foam in this gap. Heat could therefore rise undisturbed at this point and form condensation on the wood, right?

I have labeled the photos accordingly: One photo shows an overview with the marking of the four spots as well as detailed photos.

I actually wanted to check with a thermal imaging camera on cold days to see if you can really see heat rising at the affected spots and then contact the construction company. But actually, I can save myself the effort (I would have to borrow such a camera from a tool shop) and contact the company directly to ask for repairs.

What do you think?

Hi,

Am I right in understanding that at Spot 1 you can basically look down from the attic into the upper floor? Light seems to be coming through the gap?

Rising heat is not the problem (only for your heating bill), but the rising warm air. It transports a lot of moisture from the warm living area into the cold attic, and there the humidity settles on the first building component it encounters.
In short, the attic hatch and frame must be airtight. Otherwise, you won’t be able to get it under control.

Best regards,

Andreas

Hi,

do I understand correctly that at point 1 you can basically look down from the attic into the upper floor? There seems to be light coming through the gap?

Rising heat is not the problem (only for your heating bill), but the rising warm air. It transports a lot of moisture from the warm living area into the cold attic, where the humidity settles on the first available component.
In short, the attic hatch and frame must be airtight. Otherwise, you won't get it under control.

Best regards,

Andreas

That's exactly what I thought immediately.
Unfortunately, I never took a photo of how it looked in our house, but around the entire attic entry hatch there were two layers of those extremely sealing tapes. No air got through there.
I'm amazed how your house from 2020 passed the blower door test with a cold roof where there's a whole gap open?

Hi,

do I understand correctly that at spot 1 you can basically look from the attic down into the upper floor? There seems to be light coming through the gap?

Rising heat is not the problem (only for your heating bill), but the rising warm air. It carries a lot of moisture from the warm living area into the cold attic, where the humidity condenses on the first building component it encounters.
In short, the attic hatch and frame must be airtight. Otherwise, you won’t get this under control.

Best regards,

Andreas

At spot 1, I see this foil below. And under the foil are the ceiling panels (OSB) of the upper floor. So I cannot look through the gap into the upper floor. Still, warm air seems to be coming up at that spot somehow. That’s the only way I can explain the dark spots on the wood, exactly where the contact to the cold air is.

If missing insulation above the vapor barrier can’t be the cause, then the vapor barrier must be damaged somewhere or not properly installed. Although I still don’t understand this statement. Water forms at the cold/warm interface. And in this case, that would be the vapor barrier.

The cold-warm boundary is not a line but rather an area. Let's assume you have 10cm of insulation, below is 20 degrees warm air with 50% humidity, above is 0 degrees cold. Somewhere in the middle of the insulation, the point is reached where the water condenses. That is why you put the vapor barrier on the warm, moist side, so no moist air gets into the insulation and nothing condenses. You now have two problems: 1. you have various uninsulated spots. There, the boundary is a very small area 2. you have somewhere a spot where moist warm air gets through Because of this, condensation occurs and not just a little, one beam is really wet Complain and have it fixed

Our construction manager always explained to us how important the most meticulous proper sealing of the vapor retarder (intelligent foil?) or vapor barrier is. He said that in the worst case, one liter! of water can pass through a hole the size of a pinhead in one day (in the form of water bound in warm air). For sensitive components like wood, drywall, mineral insulation, etc., one liter is a catastrophe. Especially in areas that cannot be inspected (later). And he was always very keen that we (doing the work ourselves but initially under his guidance and help) executed it so well that he could sleep well ;)