crawl space vapor barrier

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1

Originally Posted By: Jim Troth
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I inspected a home in which there were no vents for the full size crawl space. However, there was a plastic vapor barrier fastened to the bottom of the joists. Is a vapor barrier enough or should there also be ventilation.


There also was a sump pump in the crawl space.

2

Originally Posted By: rcloyd
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Jim:


Is there continuously operated mechanical ventilaton provided in the crawl
space? Is the crawl space used for a supply plenum for heated or cooled air?

Need answers to these questions to determine if this is a proper application.

Regards,

--
Russell G. Cloyd
Intra-Spec Home Inspections
& Code Consulting, LLC
859-586-4591
www.intra-spechomeinspections.com

3

Originally Posted By: chorne
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Jim,


Is it a dirt floor and what is the clearance between the ground and


the floor?


The vapor barrier should be on the floor if it is dirt.
I have seen poly stapled to the bottom of the joists and
puddles of condensation built up on the upper side of it.

Carla

4

Originally Posted By: dvalley
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Jim,


Welcome to NACHI.

Carla is absolutely correct. I advise my clients to remove any plastic from floor joist areas. It traps a lot of moisture.

If it's a concrete floor below these joists, you shouldn't have any issues concerning a barrier (unless of course, its moist).

In my area, I show my clients how to condition a dirt crawl area. It's much better in my opinion.
![](upload://me4MtRe3nGBGET8vgZY42XGj9kl.gif)

--
David Valley
MAB Member

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

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

5

Originally Posted By: whandley
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1997 UBC 2306.7 Under Floor Ventilation: Under floor areas shall be ventilated by an approved mechanical means or by openings into the under floor area walls. Such openings shall have a net area of not less than 1 square foot for each 150 square feet of under floor area. Openings shall be located as close to corners as practical and shall provide cross ventilation. Where moisture due to climate and groundwater


conditions is not considered excessive, the building official may allow operable louvers and may allow the required net area of vent openings to be reduced to 10 percent of the above, provided the under floor ground surface area is covered with an approved vapor retarder.

6

Originally Posted By: Jim Troth
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There was not any type of mechanical ventilation. The floor was dirt covered with gravel. The scace between floor joist and ground was about 2 feet.


How about a home with a dirt floor basement. vapor barrier still on the floor right?

7

Originally Posted By: whandley
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Yes, vapor barrier on “Grade”. If you install insulation with a


vapor barrier between the floor joists, make sure the vapor


barrier is facing the interior living area, “Warm Side”. icon_idea.gif

8

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


Here in the south is it stapled to the underside of the floor. We have to keep the vapor barrier on the warm side, you know! icon_biggrin.gif

9

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


Are you familiar with a product that looks like foil covered bubble wrap? The company claims an R value of 16 if it is stapled/fastened to the bottom of joists. Would this be adequate for a vaper barrier and as an insulation?