Crawlspaces & Barriers: Installation Standards / Best Practices for BPI Professionals & Contractors ?

Hi There Folks,

I came across this unconditioned crawlspace barrier installed by a long-established BPI contractor. 

  • Location:  Bay Area of California- near the ocean.  
  • Environmental Factors:  The area receives a lot of rain, and is notorious for rising groundwater.  
  • Health Factors:  The customers have respiratory issues, and these were communicated to the contractor.
  • Material:  6mm visqueen, red tape, nails
  • Access:  There is plenty of room in crawlspace.  No access issues.
  • Concerns:  The material stops several inches short of the foundation walls. Some seams are taped with red tape.  Held to ground with 8 inch nails. 

I have a lot of respect for this particular contractor, but I have grave questions about how he approaches barrier installation in crawl spaces.

He has responded that this approach is adequate for unconditioned crawlspaces and that barriers only need to go up foundation walls on conditioned crawlspaces.  Hmmm...

I would appreciate insights, and direction to standards. 

Tags: barrier, crawl, space

Views: 2254

Replies to This Discussion

I am not sure what specifications the contractor used for this, but from the looks and sound of it, I would say that it is not thoroughly done or completed.  It is not going to function as a vapor barrier is the barrier doesn't cover all areas of the floor and run at least partially up the wall.  The client could have done the same thing themselves or better.  There are many really good products out there such as clean space and crawl space concepts, etc... they have everything you need to actually install the vapor barrier and encapsulate it appropriately, including how to videos.

I hope this is just temporary, maybe not yet completed and that they didn't pay for this.

Thanks Debra.

I am being told by the contractor that his material selection and installation method is appropriate for an unconditioned space, subject to ground moisture. 

He is telling me that an unconditioned, vented crawlspace should not have the barrier running up the foundation walls and that doing so that traps the moisture under the barrier.   It seems to me that we want to trap most of the moisture under the barrier....isn't that one of the objectives of having the barrier? 

You are certainly correct.

Keep in mind that the Contractor is probably trying to work within the codes for his particular area.  The ICC and energy codes are being updated.

If you are going to keep a crawl space unconditoned and ventilated, you are required to use a vapor barrier on the floor of the crawl space, which should extend up the wall quite a bit, a vapor barrier must also be installed on the underside of the floor above the crawlspace if it is conditioned space above it and insulated, and the rim joists should be sealed and the area.

Yes, the purpose of the barrier is to trap the moisture to keep it from getting into the conditioned space.  That is why best practice tells us that we run the membrane up the foundation wall, terminate it approximately 6 inches below the mud sill plate to allow for termite inspections and fasten it with mastic and mechanical fasteners.  The membrane should be at least 6 mil thickness, overlapped approximately 12 inches and sealed with a durable tape (Tyvek tape works well).  If people will be crawling on the membane to service HVAC equipment, etc, the membrane should be secured with large washered nails every 4 or 5 feet.

Keep in mind that this is a vapor barrier, not a water barrier.  If the crawl space is getting flooded during the wet months, bulk water management techiques should be addressed around the exterior of the foundation to carry water away from the structure.  If the water table is close to finish grade then a sump pump system may be in order.

Jennifer,  I'm curious why you made this post.  Are you trying to help the homeowner get compensation from the contractor?  Are you trying to assist the homeowner with legal action?  Are you trying to help the contractor get better at installing vapor barriers?  You don't state the specifications of the job nor do you tell us what inspections (if any) where done.  Why was the contractor called in?  Was there excessive moisture in the conditioned space?  Mold in the bathrooms?  Chronic sinus problems? Did you inspect the project before the installation of the membrane?  Did you verify the RH in the crawl space before and after the installation?  Please don't dump a few photos and sparse information on us and expect us to help you nail a contractor (which it sounds like this is what you are trying to do).

And Debra, your statement is not correct.  The membrane, as shown, will block about 90% of the moisture if it is installed over the entire area.  Yes, best practice does say that it should be lapped up the foundation walls and attached with mastic and mechanical fasteners but it is not required by code.  Code does require that the membrane be terminated 6 inches below the top of the concrete wall to provide for termite inspection.

Hey Ken,

This contractor is a close friend of mine who I have referred a lot of work to & have helped him connect with resources for continuing education in home performance.  There is no intention to "nail" anyone, but would like to work with him to improve installation using best practices. 

I have seen installations performed by a number of other BPI contractors in unconditioned vented spaces, and these barriers have always gone at least six inches up the foundation wall and covered the entire ground.  The pictures were just to show the visible ground & lack of foundation lapping.

Are there any instances where that method would be best practice?  Since this respected BPI contractor is telling me that this is the best practice, I am wondering if anyone else agrees- and if not, what resources are available to guide better practices.  

And yes, I was familiar with the house before the installation.  There were historic moisture problems that were mostly alleviated by french drains around the foundation.  Some moisture in crawlspace, but allergies and sinus problems were the main concern. 

Hi Jennifer,

Glad to hear that you are friends with the contractor and just trying to gain information.  His installation is not "best practice" but it is an accepted installation method.  As I mentioned in a previous post, best practice is to lay down a minimum of a 6 mil black membrane (use black instead of clear to eliminate the greenhouse effect from the sun shining in from vents), overlap at least 9 inches (I recommend 12 inches), tape joints with durable tape, lap up stem walls terminating approximately 6 inches below sill plate for termite inspection, attach to wall with mastic (duct mastic works great - wear rubber gloves with cloth gloves over them to apply.  Dispose of both pairs after installation).  Finally, mechanicially fasten membrane to wall using pressure treated members Ramset to the concrete walls.  Believe me, this is best practice and it works great.

Just remember that this is just one step in improving indoor air quality.  It sounds like your client needs to have a qualified contractor do serious air leak sealings top and bottom along with the installation of a good HRV to provide fresh air directly from the outdoors 24/7. 

Code is minimum and it appears that the vapor barrier didn't even reach the walls in areas as per the photos.  90% humidity is not going to really resolve all the issues for the homeowner who is having respiratory issues.  While I agree with you, Ken, that not a lot of information is provided, a BPI certified contractor is trained in Building Science to provide the best practices for this and other situations when it comes to health and safety issues.

Debra,  being a BPI certfied contractor, I agree but Jennifer didn't provide enough information for us to accurately assess the conditions so I stand by my 90% statement.  By the way, code is for new construction.  This is an existing structure where no permit is required to install a vapor membrane (and yes, I know we BPI certified contractors should do it right the first time but that's not what we are discussing).

Jennifer, here is a good article and there are others at this site:

I'm not a believer in vented crawl spaces but maybe in some climates there are reasons for them.  I'm also not a fan of  counting on natural (rather than mechanical) ventilation for accomplishing any goal you hope to consistently achieve.  So this all sounds a bit foreign to me.  

If you were making that space unintentionally conditioned, bringing it into the thermal and pressure boundary of the home, then the more thorough approach would be absolutely required.  But as this space is outside thermal and pressure boundaries, then having it end short of the walls might be a better approach as it won't create a pond should water somehow over top the plastic.  

Is the idea to reduce evaporation from the earth thereby reducing likelihood of condensation forming on framing above under some random conditions?  If that's the case, seems the more you cover the more you accomplish, and at some point cost effectiveness makes absurd efforts, well, absurd.  And in this case they may actually be completely counterproductive should the barrier turn into a bath tub and this condition went unnoticed. 


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