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Vapor Barrier holding Water

Northern Illinois home built in 1905. Previous owner removed lather and plaster ceiling and replaced with drywall, with vapor barrier. Insulation is above vapor barrier in attic.

We noticed water stains on the ceiling, so crawling up there, I pealed back the insulation and found water under the water vapor, above the drywall.

I don't see any holes or rips in the barrier. It is close to an outside wall.

What do I do now?

Timothy Miller
Re: Vapor Barrier holding Water

Howdy, sorry to hear of your water issue. Is there any attic vents close to the wet insulation? Have you had any wind blown snow that may of entered the attic and melted? Have you checked the roof above the area to see if any wind or hail damage? Do you have a humidifier on so the interior humidity is higher then normal.
First remove the wet insulation and wipe up any water. Then look for a roof leak source.

Re: Vapor Barrier holding Water

The insulation is not wet.

The area is near an opening in the exterior wall (in the attic for cross ventilation). I too thought wind blown snow, but the insulation was not wet.

Looking from the attic, the layers are:
1. Insulation
2. Vapor Barrier
3. Drywall

The water is between the vapor barrier and the drywall. Barrier is without tears or holes. So that would point to no leaks from above.

We have run a humidifier this winter.

How do I prevent the humidity from going through the drywall and condensing? (besides not running the humidifier - unless that is the only answer.)

Re: Vapor Barrier holding Water

More insulation may keep the temperature at the vapor barrier/ drywall above the dew point. More heat in the room may also keep the temp at the vapor barrier above the dew point.

In the old days vapor barriers weren't recommended for ceilings, with the theory that the vapor would eventually pass through and out. With the thicker insulation used today, I'm not sure that applies.

Don't know what is recommended for N. Il., but R-38 would be a minimum. The humidifier certainly can contribute enough extra vapor to cause your problem.

Timothy Miller
Re: Vapor Barrier holding Water

Howdy again, is the insulation fiberglass? if so it does not hold water but the water goes threw it to pool on the plastic. The moisture is not coming up from the home as the wetness would be below the plastic. So is roof vented properly- wind blown snow can cause this and worse....

Timothy Miller
Re: Vapor Barrier holding Water

opsee re read, if moisture is between drywall and plastic likely to much humidity in the house. Suggest turn off humidifier & be sure to use the bath fans when showering. Is the ceiling painted? There are paints you can use that are good at creating a vapor barrier so the moisture stops at ceiling before it transfers threw the drywall.

Re: Vapor Barrier holding Water

It does sound like there is moisture stacking up into the trapped space between the drywall and your vapor barrier. Whether you remove the barrier or leave it you need to have a professional look over the structure for unplanned openings, ventillation issues, moisture intrusions and other contributing factors that lead to problems like this. I've worked in the indoor air quality industry for seventeen years and seen all kinds of crazy stuff, including a guy that had the same problem, tore out the vapor barrier, relaid the insulation, just to have a mold problem later and an expensive remediation company come in to remedy his situation. There are a couple of good resources I can share with you - resources that will help you find a qualified inspector in your area: www.iaqcouncil.org and www.aiha.org. Just don't get an inspector that remediates his/her own work - conflict of interest. Get someone that can write you a protocol, but doesn't do the remediation so you can feel better about them working for you instead of against you.

Re: Vapor Barrier holding Water

I'm going to add one more thing to my last comment: Stay away from companies that advertise "toxic black mold". There is no scientific research saying mold is toxic. Some molds can produce toxins, but the ones that do require specific conditions to do so. I wish you all the best.

Re: Vapor Barrier holding Water

Just found this post and it sounds like the same issue i'm having in my upper midwest house.  any final solutions from the OP?

Re: Vapor Barrier holding Water

Adding my theory to what is happening (and we are having the same issue, so have a strong interest in getting to root cause).

I believe it is a winter issue with warm moist house air finding it's way to the attic and interacting with the cold attic air.

Naturally, the warm house air (with added moisture from the OP's humidifier) will rise and keep rising if it finds a path through poorly painted drywall and/or cracks in the drywall.

Naturally again, the cold attic air will sink down through the insulation.

This creates the classic interface at the vapor barrier with cold on one side (the attic) and warm on the other (the house).

Although the OP said he cant find any seams in the vapor barrier, it does not matter since this is a thermal issue.

It's the same principle as a glass of cold water on a hot muggy day.

  • hot muggy air outside the glass = air taht has risen from the house
  • glass = vapor barrier in the attic under the insulation
  • cold water = attic air that has sunk down thru the insulation

Just like the glass will sweat on the outside of the glass, the OP's vapor barrier is sweating on the house side.

It is not necessary to have moisture pass through the vapor barrier.

If the temperature of the air on the attic side of the vapor barrier is below the dewpoint of the air that has risen from the house, then condensation/sweating will occur.

Re: Vapor Barrier holding Water

How to solve:

  • turn off the humidifier.  if not possible, then consider increasing room circulation to avoid "dead air" spaces where warm mosit air can accumulate esp'y at the ceiling.
  • check the ceiling for any cracks or poorly painted areas.  if found, repair with a quality, moisture inhibiting primer and higher gloss paint.  look through the primers that are rated for keeping mositure off basement walls.
  • increase attic insulation, espy in the problem area


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