VApor Barrier at Ceiling.

**Mike Tracy** · 02-28-2011, 04:23 PM

Had a house today that was built in 1972. When inspecting the attic space I gound a large area of previously wet insulation and was checking for fungal growth on the ceiling drywall below this area when i found a 4 mil clear plastic vapor barrier. This is a vented attic space with roof and soffit vents. This is the first time I have seen this. What would be the concerns if any?

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Tech 9 Home Inspections · 02-28-2011, 04:44 PM

Originally Posted by Mike Tracy

Had a house today that was built in 1972. When inspecting the attic space I gound a large area of previously wet insulation and was checking for fungal growth on the ceiling drywall below this area when i found a 4 mil clear plastic vapor barrier. This is a vented attic space with roof and soffit vents. This is the first time I have seen this. What would be the concerns if any?

Thats how we do it in colder climates. Perhaps a DIY had the right idea but wrong climate??IMOP

**Scott Patterson** · 02-28-2011, 05:08 PM

Originally Posted by Mike Tracy

Had a house today that was built in 1972. When inspecting the attic space I gound a large area of previously wet insulation and was checking for fungal growth on the ceiling drywall below this area when i found a 4 mil clear plastic vapor barrier. This is a vented attic space with roof and soffit vents. This is the first time I have seen this. What would be the concerns if any?

One problem would be the moisture that you found.. Ever placed a piece of plastic wrap over a warm bowl of food? You basically have the same problem with the plastic in the attic. All of the warm moist air is trapped and then it hits that cool attic and POOF you have a tropical rain forest in the attic.

**Vern Heiler** · 02-28-2011, 05:30 PM

Originally Posted by Mike Tracy

Had a house today that was built in 1972. When inspecting the attic space I gound a large area of previously wet insulation and was checking for fungal growth on the ceiling drywall below this area when i found a 4 mil clear plastic vapor barrier. This is a vented attic space with roof and soffit vents. This is the first time I have seen this. What would be the concerns if any?

If I'm reading this right, the vapor barrier is ontop of the drywall and beneath the insulation. If so, that's exactly how it should be; vapor barrier toward the heated space.

Hector Acevedo · 02-28-2011, 06:48 PM

The vapor barrier is to be installed on the warm in winter side of the building envelope. The problem may be that the vapor barrier should be 6 mil thick and all overlapping joints should be sealed. Accustic sealant should be applied at the bottom and top plate of the walls prior to installation. If there are any penetrations through the vapor barrier such as a tear or joints that are not sealed, the end result is condensation.

**John Kogel** · 02-28-2011, 07:03 PM

Originally Posted by Hector Acevedo

The vapor barrier is to be installed on the warm in winter side of the building envelope. The problem may be that the vapor barrier should be 6 mil thick and all overlapping joints should be sealed. Acoustic sealant should be applied at the bottom and top plate of the walls prior to installation. If there are any penetrations through the vapor barrier such as a tear or joints that are not sealed, the end result is condensation.

That is all very well now, but not expected in a 1972 house.

My advice to the OP is to go with local standards. The vapor barrier was a fairly new concept in the 70's. Standards may have changed.

The home owners can seal the hatch and light fixtures, and paint ceilings with vapor barrier-type paint. This will help keep moisture from getting past the drywall.

**John Kogel** · 03-01-2011, 11:46 AM

A poly vapour barrier is required on the warm side, behind the drywall, in most of the colder regions, including all of Canada, AFAIK.
I spotted this dark patch in a 1980's attic recently. Mold doesn't grow on clean fiberglass, but it will grow on the dust layer on top of the f/g. The other requirement is mild temp and moisture.
I dug thru and saw the top plate of an interior wall. There is a breach in the vapor barrier here, allowing interior moist air to hit the cool air in the attic and condense.
This shows why new building methods call for a poly strip laid over the top plate before the ceiling joists go on to provide a gasket for the vapor barrier.

You can see the poly on top of the drywall in the lower left and upper right areas of the hole.

Rick Hill · 03-01-2011, 03:28 PM

My thoughts are that if the moisture is under the plastic there may be a hole in the insulation blanket. If the water is on top of the plastic it could be a roof leak that just drained through the insulation until it met the plastic layer.

Jason Edwards · 03-02-2011, 08:17 PM

Similar issue. This attic has a ridge vent, as well as soffit vents (but they are blocked) and no vapor barrier under the loose insulation. I observed no moisture issues in the drywall. My concern is, if the homeowner clears the soffits and adds rafter vents for attic-quate (sorry) ventilation, will they will suddenly have moisture issues in the drywall because of the increased temperature contrast between the attic and living space that the proper ventilation will probably create? Please see attached. This is PA about 20 minutes from Philly. Suggest removing loose insulation and laying down faced rolls? Don't even bother?

**Robert Hronek** · 03-04-2011, 10:52 AM

Originally Posted by Hector Acevedo

The vapor barrier is to be installed on the warm in winter side of the building envelope. The problem may be that the vapor barrier should be 6 mil thick and all overlapping joints should be sealed. Accustic sealant should be applied at the bottom and top plate of the walls prior to installation. If there are any penetrations through the vapor barrier such as a tear or joints that are not sealed, the end result is condensation.

Sioux City is not far enough north to worry about it in the attic. There should not be condensation on the poly as long as it has a r10or more of insualtion. The poly would stay above the dew point as it is on the warm side of hte insulation. Any vapor making it through should be able to dry to the attic. At the OP alluded to home around here do not use poly above the ceiling.

In a closed cavity like a wall you should seal the poly but it is never done around here. SC is 90 miles from me. Actually we should be getting rif of poly except in the extereme north part of US. Northern MN, Canada and Alaska are the few areas that need it along with the humid southeast.

Vapor diffusion through materials is not the major source of moisture. Air leaks carry the moisture. Poly usually has many punctures that let air and moisture in and then traps it in the wall. A better approach is to air seal home and use dense pack. Dense pack stops the convection carrying the moisture. House wraps are not air barriers they are wrb's