View Full Version : Ground in crawlspace

Jeff Eastman
04-14-2007, 08:40 PM

Jeff Gainey
04-15-2007, 06:50 AM
I always make the recommendation of a moisture barrier being installed. I have a lot of crawls in my area and frequently have to discuss that issue. I will tell them that after it is properly installed with at least 12 inch overlaps (after the debris is removed) and extended up the foundation walls at least 4-6 inches to monitor water levels for a few months to see what, if any, issues with standing water is present. If water pools in the plastic I tell them to just cut a small slit to allow drainage underneath. If they have standing or puddled water on top of their newly installed moisture barrier, there is either a need for additional water removal methods(sump system) or an active leak needing to be fixed. Here are a few from this week.

The pictures show 3 different crawls done this week. The first one would be an easy upgrade due to good height. The 2nd had a moisture barrier down in only some areas and "might as well set the pressure tanks on the ground. It was good enough for the first one.
The 3rd is one that had it down almost everywhere but missed along the lat 4-6 ft along the north wall. Guess where the fungus stained joists were located?
I hope this helps...Jeff G

Rick Hurst
04-15-2007, 06:50 AM

Even though it may be required, I personally do not see it here under new construction of pier and beam homes.

I've litterally crawled probably a 1000 plus home in my time, and I can say everyone of the homes that had a mold issue or serious wood decay have the vapor barrier under the home.

I don't think it is ever installed as it should be. It is bunched up around the piers and has large openings which still allows moisture to evaporate and condense on the bottom of the structure componets.

Numerous ones I've seen pools of water sitting on top of the plastic which then does not allow the water to evaporate or even soak back into the ground.

Ever crawl a 100 yr. home. Don't see moisture barriers under those, yet most of the wood under the much older homes usually do not have the mold and decay as others.

I think overall it (vapor barrier) on a pier and beam is a bad idea. I think that ventilation of the crawlspace is a very important idea, yet we have folks saying its not even necessary.

Mostly, I think it all depends on your location and conditions present. Is the drainage poor around the home, is there enough ventilation...

But to your question, No I don't encourage it nor do I recommend it. Thats just myself. Others will disagree.

Jim Robinson
04-15-2007, 08:29 AM
I've only seen it a few times in my area. Vegas is pretty simliar climate. If the crawl is vented here, it's pretty rare for any moisture to be present. I don't mention it at all if the crawl is dry, which is most of the time (thank god).

Jeff Gainey
04-15-2007, 01:51 PM
I suppose it matters where in the country you are located, but in the crawl spaces I have traveled, the majority of the problem crawls are lacking moisture barriers and are the most important item in the crawl to add. I find where there are partial barriers or improperly ones installed, the deterioration is always where the barrier is missing. The only crawls I have seen where the moisture barrier is present and there are moisture problems, is where the builder has buried the plastic under 4-6 inches of gravel which turns it into a liability because then it does trap the water above it. With proper overlap and carrying it up the sides of foundation walls at least 6 inches, the only way moisture can get above it is to flood the area which indicates more water control measures are needed, or a leak in the plumbing system which it would identify by the wet plastic in that area. I give my clients the link to this website for additional info on water control and the concept from Jos L's building science website.
If the concept of water movement is to be understood to go from hot to cold and less to more, then why do they make crawl vents that open up in the summer when the humidity is trying to get into the cool crawl space.
Inquiring minds would like to know...Jeff G

Here is a picture of a crawl without a moisture barrier left to grow...

Tim Moreira
04-15-2007, 10:53 PM
I would think that proper ventilation of the crawl would be more important.

Jeff Gainey
04-16-2007, 05:04 AM
The pictures I included above were well ventilated with foundation vents. Jeff G

David Banks
04-16-2007, 05:27 AM
"Mostly, I think it all depends on your location and conditions present. Is the drainage poor around the home, is there enough ventilation..."

I agree with Rick. Some you go in have issues others do not. I have been in many 100 year old crawl spaces all with no vapor barrier. Some with ventilation some open to basement only. No problems. Dry as a bone. In this case I tell people it has worked for 100 years why change it.
Then I go on to tell them the importance of a vapor barrier.:)

Mike Schulz
04-16-2007, 02:37 PM
In our area it's a must specially if its clay soil. Sandy soils seem less of a problem. I tell my clients to close there vents in the summer (humid) and open the rest of the time. Freezing is not a issue most of the time.

I also have seen 100 year old homes with no problems but they where not insulated. The insulation is what holds the moisture.

Correct to landscaping and drainage on the outside, install vapor barrier except under a air handler and close vents during humid months. That typically solves most problems. High water table is another issue.

The new kid on the block, and I hope it becomes mandatory, is sealed/conditioned crawl spaces.

Mike Schulz
04-16-2007, 02:41 PM
I would think that proper ventilation of the crawl would be more important.

Tim, Tim ,Tim. That coming from a slab state. You have to be here to experience it.

Terry Neyedli
04-18-2007, 05:54 PM
More often then not a bare ground in a crawl space will produce vapour. In our west coast climate it is a given. Mould, mildew or fungi develop very quickly and can turn to a very unhealthy environment.
I always strongly urge that the bare earth be properly sloped, covered fully with a vapour barrier, be properly vented (ambient or mechanically) and inspected every season.


Richard Rushing
04-18-2007, 10:59 PM
I have to agree with Rick Hurst. Since he and I inspect in the same general area, we both see quite alot of these without a vapor barrier and it's dry as a bone under there.

I have recently done construction inspections on new home that had the cadalliac of all crawlspace vapor barriers and moisture control designs that I have been privy to examine. The vapor barriers were installed over gravel, The vapor barrier had nicely overlapping joints of 12", swales were cut into the sides under the home to direct water to the exterior downspout tie-in. Also, A set of two sump pumps were present as well as two mechanical vents.

Dry as a bone down there.


Rick Bunzel
04-22-2007, 04:56 PM
Here in the Pacific NW it is a requirement. We get lots of ground moisture as well as water intrusion under the foundation footing and the vapor barrier is the first line of design. I have crawled some that resembled a water bed and since the seams were sealed I didn't have a major issue as the system was functioning as it should. Most likely if I did that same crawl in April (today) the water would be gone. About 60% of the crawl spaces have water or evidence of past water. If the builder would run the vapor barrier up the walls and tape the seams most of these problems would not be there,


04-23-2007, 04:42 AM
Poor grading and hack jobs make some beyond repair or upgrade.

Ken Meyer
05-05-2007, 08:21 AM
Could the reason that older homes don't have a moisture problem be in the fact that they are not very air tight, and the water vapor has plenty of ways to move up through the structure and evaporate out?

Jerry Peck
05-05-2007, 08:26 AM
Could the reason that older homes don't have a moisture problem be in the fact that they are not very air tight, and the water vapor has plenty of ways to move up through the structure and evaporate out?

That and air blowing through them takes moisture with it.

Seal an older home up tight and you will have the same problems a brand new home has - how on earth do I extract all that moisture without creating a negative pressure in the house which will just pump more moisture in from outside.

Victor DaGraca
05-05-2007, 11:45 AM
I have never tested the theory, however, I have been told by an instructor that if you do place a moisture barrier in a crawl, to do it gradually.
for instance;
That damp crawl space is keeping the flooring and all components attached to it at a certain "moisture level"
Once you apply a barrier, you are eliminating the source of moisture that is keeping that cellular material at its current "swolen" condition (for lack of a better term).
That cellular material now begins to shrink and, if the shrinkage is rapid enough, cracks will begin to appear.
His recommendation was to leave an area about 3' wide at the perimeter uncovered, and slowly, over a period of weeks or months, move the barrier towards the foundation until it covers all the ground.
I guess the theory was that if done slowly enough the structure will acclimate and minimal damage will occur.
Personally, I dont understand how eliminating moisture gradually will minimize shrinkage. Shrinkage is shrinkage, gradual or otherwise.

Anyone ever had a shrinkage problem? other than Seinfeld's Costanza?

Matthew Bartels
05-08-2007, 10:15 AM
Mike Schulz
"In our area it's a must specially if its clay soil. Sandy soils seem less of a problem. I tell my clients to close there vents in the summer (humid) and open the rest of the time. Freezing is not a issue most of the time."

Close the vents in summer!?! That’s when they are needed the most!
My opinion of the crawlspace is the exact same as the attic. You can't vent or seal it half assed either way.
If the crawl is to be sealed, (closed vents) than it must also be insulated and conditioned just like the rest of the house. The vents should not only be closed, but completely, 100% sealed. Closing a cheap plastic vent in a foundation wall during July will not keep humidity in the crawlspace down, but will only make it worse.

If the crawlspace is to be vented, (open vents) the interior should be completely sealed from the crawlspace. Any ducts in the attic or crawl (bad idea to begin with) should be well sealed and insulated to prevent the conditioned air from being released into the crawl space or being pumped into the building envelope.

Mike Schulz
"install vapor barrier except under a air handler and close vents during humid months. That typically solves most problems."

I would think a vapor barrier under the air handler close to the ground would be a good idea. What would be the problem with that?

O.K. now everyone put in your 2 nickels on the open or closed debate. I would love to hear what everyone else thinks.

How do you fellers use that fancy quote feature?

Richard Rushing
05-08-2007, 01:02 PM
Us fellers use that high follutin "Quote" button at the lower bottom right hand corner...;)

Rodney George
05-09-2007, 09:12 AM
No I do not recommend it. It is not required by Code. I believe it would be an upgrade to the house. If I recommend it then the buyer will want the seller to do it.

Mike Schulz
05-10-2007, 03:27 PM
I have tested my theory over the years. I also see the saturated insulation shredding from holding the water. Yes a sealed close space would be nice. But it works the way I posted. My home is setup just like I stated and it cleared up my problem. Do a little research and see for yourself.
Mathew I am quite surprised you live not far from hear and you haven't noticed the moisture levels during the humid months.:confused:

I don't like it under a furnace or air handler. If it condensates or clogged condensation line it will lay on the plastic instead of the soil sucking it up.

Matthew Bartels
05-11-2007, 08:03 AM
Hey Mike,

I see the moisture soaked insulation falling from the joists all too often. Every time I see it, it is in an area that is poorly vented and/or has water problems from improper grading, leaky pipes, leaky ducts and air handlers, etc.

There is no debate on the standing water issue from the above mentioned sources. None is best.

As far as venting out humid air in July, I would think that open vents would be better. If the installed wall vents are not enough, adding a powered fan may be another option. I would think that closing a plastic vent would still let a fair amount of humid air to enter but make it even harder to get out. If the vents are fully sealed and the crawl is conditioned and/or dehumidified, that would be a different story.

I will do a highly unscientific test measuring the humidity and temps relative to the exterior on my own crawlspace this year as soon as we get a nice long hot and humid snap. That shouldn’t be too far away!

Mike Schulz
05-11-2007, 11:07 AM
The area that you are speaking of is where the Humid air/condensation collects because of the poor design of where the vents are installed. That is why I closed mine off and my crawl stays dry now. Here is something you should read.

Thom Walker
05-11-2007, 12:31 PM
I have done a ton of reading on this and have worked on them in three distinct climate areas over the last 25 years. I've come to believe that the placement of it in predominantly arid areas has little value. The placement of barriers in humid areas should be required. Here are some additional sample readings.

www.buildingscience.com/resources/foundations/ (http://www.buildingscience.com/resources/foundations/)

www.homeadditionplus.com/basement-info/Control-Moisture-in-Ventilated-Crawl-Space.htm (http://www.homeadditionplus.com/basement-info/Control-Moisture-in-Ventilated-Crawl-Space.htm)

www.srmi.biz/Tips.Moisture___Pollution.Crawl_space_moisture.htm (http://www.srmi.biz/Tips.Moisture___Pollution.Crawl_space_moisture.htm )

www.askthebuilder.com/543-Crawl-Space-Vents.shtml (http://www.askthebuilder.com/543-Crawl-Space-Vents.shtml)

www.thisoldhouse.com/toh/tvprograms/asktoh/qaarticle/0,16588,441684,00.html (http://www.thisoldhouse.com/toh/tvprograms/asktoh/qaarticle/0,16588,441684,00.html)

http://southface.org/web/resources&services/publications/technical_bulletins/CI-Crawlspace%2000-774.pdf (http://southface.org/web/resources&services/publications/technical_bulletins/CI-Crawlspace%2000-774.pdf)

www.hud.gov/offices/hsg/sfh/ref/sfhp1-25.cfm (http://www.hud.gov/offices/hsg/sfh/ref/sfhp1-25.cfm)

www.soundhome.com/topics/topic_basement.shtml#101 (http://www.soundhome.com/topics/topic_basement.shtml#101)

www.fpl.fs.fed.us/documnts/techline/crawl-space-ventilation.pdf (http://www.fpl.fs.fed.us/documnts/techline/crawl-space-ventilation.pdf)

www.eere.energy.gov/consumer/your_home/insulation_airsealing/index.cfm/mytopic=11780 (http://www.eere.energy.gov/consumer/your_home/insulation_airsealing/index.cfm/mytopic=11780)

Matthew Bartels
05-11-2007, 05:54 PM
I think were comparing apples and oranges here. If a crawlspace is SEALED, that is O.K.

Simply putting up the plastic flapper on a crawlspace vent is not sealing a crawl space.

I have read all of those articles and books from Building science corp. (Highly recommended reading)

It’s when I see the ones that are “half done" or are of "poor design” where I have seen the most problems.

Crawl Space Vents (http://www.askthebuilder.com/543-Crawl-Space-Vents.shtml) (Good link Thom) This guys says were both right...or wrong. Depends on how you look at it.

Matt Fellman
06-13-2007, 12:47 PM
This has got to be a regional thing... In Oregon it's a must do. An old house that didn't have one for years and years is way more likely to have insect infestation problems, particularly boring beetles.

Mike Schulz
06-13-2007, 04:09 PM
A vapor barrier is a must. In my situation it was not enough. During the humid months the moisture was collecting on the cold surfaces until I sealed off my vents. I check it regularly and it's dry as a bone and not stale smelling.
About every home I inspect has a crawl space. Theres always mildew on the joist and insulation and they have a vapor barrier. That is why I tell them to adjust the vents as needed and check to make sure it's dry.

Bruce King
06-13-2007, 04:46 PM
Good discussion...

The reason for the variety of opinions is mostly due to the variety of climates, presence of floor insulation, slope of the lot, soil type, ground water and lack of gutters or long term clogged gutters.

Many bad crawlspaces with a vapor barrier did not have the vapor barrier present for the majority of the time.

Each problem house will require different steps for improvements.

I see many new high end homes with properly sealed crawls now.
Many have a commercial grade dehumidifier installed also.

New homes are hard to figure sometimes because the mud line around the foundation may have been caused before the floor and roof were installed.
Also water in the crawlspace was put there by the pressure washing crew.

The number one crawlspace problem I see on older homes (with floor insulation) is from lack of gutters, improper grading and no vapor barrier present until it was too late.