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What about encapsulated crawl spaces?

I have only come across a couple of encapsulated crawl spaces, but both were performing as advertized.  I used to have my worries about them and the building codes do not have a provision for allowing them as some of them are installed. 

The building codes allow for having crawl spaces that are unvented but the spaces are required to communicate with the indoor environment—in other words they are heated spaces—conditioned spaces.

This last one I inspected specifically recommends closing the crawl space vents.  My knee-jerk reaction was that in time this is going to be an issue.  However this one was ten years old, un-vented, not communicating with the indoor environment and had wood moisture levels WAY below normal for our area for even properly ventilated crawl spaces.  Moisture levels were actually quite similar to conditioned spaces I have tested.

How can this be?  The answer lies in the fact that if the crawl space is truly sealed—I mean REALLY sealed, how can moisture build up in the space?  Over time the sealed space can only make balance with moisture levels in the rest of the structure—albeit very slowly.  Even very minor gaps in the barrier will not affect the installation appreciably.  The only gaps I could find were around the pipe that ran into the sump pit. In this next picture one can see where two of the original crawl space vent locations are covered and sealed.

For moisture to move—there has to be a pathway of “air movement.”  Stop the air movement and you will succeed at stopping or minimizing the moisture movement as well. 

One of the inherent problems with vented crawl spaces is that the stack effect (upward pull of air created in any house) as well as negative pressures created by exhaust equipment, will try to pull air from the crawl space into the indoor environment.  Thus moisture and anything else in the crawl space air can be drawn into the home.  Sealing the crawl space will help minimize this issue as well.

I think in times the building codes will make adjustments to allow this type of installation, but for now the installers of the system will continue to provide letters attesting to its being OK to close the vents.

At this point I have to agree with them.

 

Charles Buell, Real Estate Inspections in Seattle.

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Seattle Home Inspector

 

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Comment balloon 21 commentsCharles Buell • December 26 2013 05:30AM

Comments

Hi Charles,

I hope you had a very Merry Christmas.

The crawl spaces here are usually not vented or very poorly vented. The sellers don't like it when I find the un vented crawl spaces.

Nice pictures and a very good post.

Have a great day in Seattle my friend.

Best, Clint McKie

Posted by Clint Mckie, Desert Sun Home, Comm. Inspection 1-575-706-5586 (Desert Sun Home, commercial Inspections) almost 5 years ago

I saw this once on a Habitat for Humanity house (had a post) and the space was entirely encapsulated, top, bottom and sides.  It looked excellent.  But it was brand new.  Interesting to see one in your area looking so dry, with so much natural moisture about.

Posted by Jay Markanich, Home Inspector - servicing all Northern Virginia (Jay Markanich Real Estate Inspections, LLC) almost 5 years ago

Clint, I don't know your area but many areas in the south do not recommend venting crawl spaces at all.  I would think this would be a good solution in the south, even more so than the north.

Jay, I will be following these things pretty closely to see how they work out.

Posted by Charles Buell, Seattle Home Inspector (Charles Buell Inspections Inc.) almost 5 years ago

I haven't seen too many of these personally Charles; I wonder how the moisture builds up behind the barrier. 

Posted by Tom Arstingstall, General Contractor, Dry Rot, Water Damage Sacramento, El Dorado County - (916) 765-5366, General Contractor, Dry Rot and Water Damage (Dry Rot and Water Damage www.tromlerconstruction.com Mobile - 916-765-5366) almost 5 years ago

Tom all of these systems come with proper drainage systems, including emergency sumps.  You would not want either a swimming pool or a reverse swimming pool

Posted by Charles Buell, Seattle Home Inspector (Charles Buell Inspections Inc.) almost 5 years ago

Cause and effect never fails to capture my attention...thank you for this post

Posted by Richie Alan Naggar, agent & author (people first...then business Ran Right Realty ) almost 5 years ago

I have been in agreement with this technique for years. Lets also consider this for a moment. When the stack effect is occurring, the outside temperature is "cold". Temperature differntial creates the effect. Cold air is dry air even with a high RH. Air leakage into the space will not significantly impact the RH due to a higher temperture in the crawl spece. In fact the RH will increase, dropping the dew point, lowering the over all moisture. 

Posted by James Quarello, Connecticut Home Inspector (JRV Home Inspection Services, LLC) almost 5 years ago

Richie, there will always be cause and effect for sure

Jim, exactly.  Sometimes it can be quite difficult to explain this to someone.  They think that because it is raining outside in the winter in Seattle that it is going to make there crawl spaces wetter--not so. (unless of course it is getting in there by flooding.)

Posted by Charles Buell, Seattle Home Inspector (Charles Buell Inspections Inc.) almost 5 years ago

Interesting...I have never seen one of these live, but I have in basement waterproofing flyer

Posted by Kristin Johnston - REALTOR®, Giving Back With Each Home Sold! (RE/MAX Realty Center ) almost 5 years ago

Kristin, just be very wary of any basement water-proofing system that does not involve work on the exterior of the foundation and drainage system.

Posted by Charles Buell, Seattle Home Inspector (Charles Buell Inspections Inc.) almost 5 years ago

Charles, 95% of my inspections include crawlspaces, and I have seen my share of encapsulated crawlspaces. I enjoy my life more when they are encapsulated. I have yet to see one with problems. I stay dry and clean and happy :). The only thing I don't like is that I can't inspect the foundation wall, or inspect for termites.

Posted by Juan Jimenez, The Richmond Home Inspector (A House on a Rock Home Inspections LLC) almost 5 years ago

Juan, the clean, dry and happy part is surely a good thing

Posted by Charles Buell, Seattle Home Inspector (Charles Buell Inspections Inc.) almost 5 years ago

Hi Charles - With high levels of radon not uncommon, we typically see this on any property with a crawl space that has to be remediated for radon, although the focus of the encapsulation is keeping out gas entering the home from the soil. And with a semi-arid climate, moisture levels aren't so much of a problem.

Posted by Dick Greenberg, Northern Colorado Residential Real Estate (New Paradigm Partners LLC) almost 5 years ago

Dick this system would be a no brainer if radon is a concern.

Posted by Charles Buell, Seattle Home Inspector (Charles Buell Inspections Inc.) almost 5 years ago

The same difficulty in understanding can be said for the other end opposite the crawl space or basement, the attic. People have a hard time understanding the warm air and the moisture in it from the conditioned space, becomes very moist air once it makes it way into the attic and cools off. So often this is diagnosed as a lack of adequate ventilation, when we know that may likely not be the problem at all. 

Posted by James Quarello, Connecticut Home Inspector (JRV Home Inspection Services, LLC) almost 5 years ago

Jim, people love to make rocket science out of paper airplanes :)

Posted by Charles Buell, Seattle Home Inspector (Charles Buell Inspections Inc.) almost 5 years ago

Hope you had a fantastic Christmas and are ready for 2014!

Posted by Barbara-Jo Roberts Berberi, MA, PSA, TRC - Greater Clearwater Florida Residential Real Estate Professional, Palm Harbor, Dunedin, Clearwater, Safety Harbor (Charles Rutenberg Realty) almost 5 years ago

They have become quite popular in my area Charles, and I have to admit, buyers seem to like what the inspections are showing.  Low level moisture even after heavy rains, wood is dry and shows no signs of moisture.  I am considering a retro fit sealing of my office.

Posted by Tammy Lankford,, Broker GA Lake Sinclair/Eatonton/Milledgeville (Lane Realty Eatonton, GA Lake Sinclair, Milledgeville, 706-485-9668) almost 5 years ago

Barbara-Jo, I am ready---bring it on!

Tammy, I have heard that--seem like a good idea to me

Posted by Charles Buell, Seattle Home Inspector (Charles Buell Inspections Inc.) almost 5 years ago

We learn something new every day.  We don't have a lot of crawl spaces in our area, but that sure is something to think about!

Posted by Yvette Chisholm, Associate Broker - Rockville, MD 301-758-9500 (Long & Foster Real Estate, Inc.) almost 5 years ago

Yvette, I sure like it when crawl spaces can be avoided

Posted by Charles Buell, Seattle Home Inspector (Charles Buell Inspections Inc.) almost 5 years ago

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