Plastic under house

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1

Originally Posted By: Steve Unger
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I just bought a house in North Texas. It has plastic covering the ground under the pier and beam foundation. I have been given different information as to what to do with it. I does collect water droplets between it and the ground. I need more ventilation, which I am adding, but I’m not sure that has an effect.

–
Steve Unger

2

Originally Posted By: lungar
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Hi! Steve


I understand that is called a vapor barrier to keep moisture out of the home from the soil in the crawl space.

3

Originally Posted By: dvalley
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Steve,


The vapor barrier you are referring to is highly recommended over all dirt crawls. When you see water droplets on the underside of the plastic, it?s a good sign. This moisture you are seeing is better under this barrier than into your sub flooring.
The thickness of the polyethylene barrier should be a minimum of 6 mil., but the thicker the better. When installing these sheets of plastic, make sure they overlap each other by at least 4 inches and are taped. You should also span this plastic sheet at least 6 inches up the side of each wall, held in place with stone or 2 X 4?s.
Without this barrier, you?ll eventually receive moisture problems throughout your sub floor area.
![](upload://aWTRUraNtQ2T2bkVBw0PHLo76ZQ.gif)

--
David Valley
MAB Member

Massachusetts Certified Home Inspections
http://www.masscertified.com

"Some cause happiness wherever they go; others, whenever they go."

4

Originally Posted By: jhagarty
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David:


Interesting comment that you had made.

I have recently attended PCO Recertification CE training where it was stated that the Vapor Barrier within a crawl space should end within 18 inches of the foundation.

The coverage of a vapor barrier or Ventilation is not the determining factor. The Moisture content within the crawl is more important. This may vary by geographic area.

--
Joseph Hagarty

HouseMaster / Main Line, PA
joseph.hagarty@housemaster.com
www.householdinspector.com

Phone: 610-399-9864
Fax : 610-399-9865

HouseMaster. Home inspections. Done right.

5

Originally Posted By: rray
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There’s some information out there on the web that I read about a year ago about totally sealing the crawl space–doing away with all ventilation and installing plastic vapor barrier over everything. Their contention was that it is better to keep all moisture out than to ventilate and let moisture move freely. It was a pretty neat article and some awesome pictures.


![icon_twisted.gif](upload://xjO326gspdTNE5QS3UTl0a0Rtvy.gif)

--
Home inspections. . . .
One home at a time.

6

Originally Posted By: dvalley
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Venting crawlspaces is a bad idea. Code requires 1 sq. ft. of ventilation for every 150 sq. ft. of dirt floor. Using a vapor barrier over the dirt floor reduces the ventilation requirement to 1 ft. per 1500 sq. ft. of floor space. The intent is to vent out the humidity that the exposed earth lets in.

But, venting creates its own problems. In winter, there's an energy penalty: cold floors and higher heating bills. In summer, vents actually admit moisture in the form of warm, humid air. Warm air can hold more moisture than cool air. Warm air entering a cool crawlspace can reach its dew point and give up its moisture as condensation. That?s not good. Relative humidity, dew point and the stack effect combine to make crawlspace vents more likely to compound a moisture problem than to alleviate it.

For these reasons, I recommend to my clients to close the vents outside and seal them from the inside with 2-in. thick foam insulation and polyurethane caulk.


The following changes that were approved by ICC on September 2003

R408.2
Delete all exceptions and add a new Section immediately following.
Unvented crawl space. Ventilation openings in under-floor spaces specified in Sections
R408.1 and R408.2 shall not be required where:
1)
Exposed earth is covered with a continuous vapor retarder. All joints of the vapor
retarder shall overlap by 6 inches (153 mm) and shall be sealed or taped. The
edges of the vapor retarder shall extend at least 6 inches (153 mm) up the stem
wall and shall be attached and sealed to the stem wall,
2)
And one of the following is provided for the under-floor space:
a. Continuously operated mechanical exhaust ventilation at a rate equal to 1
cfm for each 20 ft
2
of crawlspace floor area, including an air pathway to
the common area (such as a duct or transfer grille), and perimeter walls
insulated in accordance with Section N1102.2.8,, or
b. Conditioned air supply sized to deliver at a rate equal to 1 cfm for each 20
ft
2
of under-floor area, including a return air pathway to the common area
(such as a duct or transfer grille), and perimeter walls insulated in
accordance with Section N1102.2.8, or
c. Plenum complying with M1601.4, if under floor spaces used as a plenum.
Supporting Statement:
The new code has option for non-ventilated crawlspace that requires a polyethylene
ground cover and wall insulation to bring the crawlspace into the living space.
Basements and crawlspaces that are not within the insulated building envelope with
concrete surfaces such as walls and slabs have surface temperatures as low as 55 Deg F in
the summer. Ventilation with hot humid air in the summer with a dew point higher than
the surface temperature of the concrete results in condensation and mold growth.

--
David Valley
MAB Member

Massachusetts Certified Home Inspections
http://www.masscertified.com

"Some cause happiness wherever they go; others, whenever they go."

7

Originally Posted By: phinsperger
This post was automatically imported from our archived forum.


seal the vapor barrier to an older stone rubble foundation? The irregularities are so dramatic I can’t imagine how this can be done with causing many breaches and forcing the moisture to be concentrated at the floor just above the foundation walls.

–
.



Paul Hinsperger
Hinsperger Inspection Services
Chairman - NACHI Awards Committee
Place your Award Nominations
here !
8

Originally Posted By: wrobedeau
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Attach a 2x4 to the wall. Fill all openings between the wall and 2x4 with closed cell foam. Attach plastic to 2x4 with polyurethane sealant.


Bill Robedeau

9

Originally Posted By: phinsperger
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I wondered about something like that. My house is an 1870 house with such a foundation. I’m not confident that the old lime mortar is strong enough to hold any kind of anchor. Really didn’t want to drill into the stones themselves as it is a pain in the a-- icon_mad.gif but I guess I don’t have much choice.

–
.



Paul Hinsperger
Hinsperger Inspection Services
Chairman - NACHI Awards Committee
Place your Award Nominations
here !