That ground barrier will ALWAYS be wet on the ground side.

Thank you bus_driver for responding. I did not know that, as this is the first time I've been involved in crawl space improvement. It did un-nerve me some to see that so thanks for clearing that up for me.

Isn't it still going to collect mold? Was there mold down there before?

No, no mold before snookums2.

I would be concerned trapping moisture like that under plastic would create a mold situation. Mother nature knows best. Things need to breathe.

Think of a crawlspace as nothing more than a very short basement. It has similar waterproofing needs in order to keep the mosture out of the home. The whole point of a poly moisture barrier is to keep that moisture out of the house where it will do harm. It's why crawlspaces smell musty to begin with. They are full of moisture. Thus the popularity of encapsulated crawlspaces as an emerging trend.

Holly is right.
and yes you do need to finish the area with no vapor
barrier on the ground.

I'd do 3" of closed cell foam on the undersides of the
floor. this will seal all air leaks & add R-21 to floor.

before installing foam, mastic seal all ducts,
plenums to equipment. then from inside the house
use Hardcast brand 1402 mastic tape to seal the
gap around the supply boxes (boots)
remove supply grill, use mastic tape to seal from
flooring into the supply box, replace grills.

kudos for helping to install vb. tape all seams &
seal to walls of crawlspace & around any footings.
you want the vapor barrier as leak free as possible.

whats your location?

best of luck.

Thank you all for your insightful comments. I am in climate zone 5: hot and humid summers, often cold, snowy winters, my area is costal plain, marine clay.

To prepare for conditioned crawl spaces from currently vented, current clean up of my two crawl spaces has consisted of removing all debris, full inspection for mold and termites (none), properly sized entrances, installation of lights, removal of very old batting between joists (big sq. Ft job), inspection and cleaning of all accessible vents and supplies and return with metal fixes where necessary then application of gray paintable mastic to all seams and joints with more needed. I do wonder if I should add leveling white mastic on the big vent pieces which is thicker. I might invest in butyl tape-IRC code UL 181 and place it over the big seams or sharp corners of ducts and mastic over that still. While the grade is toward the front, I need to check that as well as consider second sump pump or at least connection at low point through original foundation wall to basement sump pump or other. Work in progress.

I am using IRC 2009 Crawlspace guidelines as below and will attempt to condition the spaces by following this guideline from the code:

'2.2. Conditioned air supply sized to deliver at a rate equal to 1 cubic foot per minute (0.47 L/s) for each 50 square feet (4.7 m2) 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 N1102.2.9;'

One crawl space is 1200 sq. Ft, so delivery of supply air at 1 cfm per 50 sq. Ft means constant 24 cfm right? It turns out I already have an open return just hanging there. An hvac specialist is helping me with this btw. The other crawl I have yet to measure but there appears to be a supply in there already too. So this part takes specialty work.

energy_rater_la - I am perplexed on whether to place 2' foam board on the perimeter interior cinderblock walls (less than 3 feet with 3' termite gap at top) and the rim joists and leave the floor joists unfoamed as Joe Lstiburek remarked to permit primarily a radiant (downward) heat crawl space environment with wood floor above. I will be having exterior foundation excavation done soon and waterproofing or other will be applied exterior then. I don't want to a) capture water between the exterior /interior cinder foundation by treating both walls nor b) find out next spring after another wet cold winter I should have placed foam not only in the rim joists but in between. Any thoughts on this?

Thank you, btw, this has been an intense amount of learning out of my specialty area as well as hands on helping and grunting.

Readings/references which have helped tremendously:

Martin Holiday:
http://www.greenbuildingadvisor.com/blogs/dept/musings/building-unvented-crawl-space

http://www.buildingscience.com/documents/information-sheets/crawlspace-insulation

http://www.buildingscience.com/documents/bareports/ba-0401-conditioned-crawlspace-construction-performance-and-codes

Here is a link that might be useful: Conditioned crawlspace and code

The vapor retarder is just doing it job: stopping moisture from entering the crawlspace. For mold to grow there must a source of food. Since the food (cellulose in the wood framing) is now above the vapor retarder, there should be no problem.

The idea that things need to "breathe" is commonly misunderstood. "Breathing" in construction is just a misleading way of saying moisture needs to have a path out of building materials and interior spaces. Keeping moisture in the earth instead of letting it enter the crawlspace or the house serves the same purpose.

Thank you renovator8. Always appreciate the insight of you and other commenters on GWeb.

Mid Atlantic location: just outside Washington DC
Climate zone 4A moist
West facing house.

Thanks.

we are such different climates!

so you know how difficult it is to work in the crawlspace,
as you've done it. (lights even...)
if you are having an exterior evacuation done...
what if you put the foam sheathing on the exterior?
sure would be easier than working it from
inside the crawlspace.

as always, I question the foam sheathing install.
in my climate we can't put foam board next to the
ground as there has to be a break of exposed block
so that termite trails can be seen.

would this be a concern for your climate?

would it be easier/more cost effective to spray
the walls from inside the crawlspace?
the way I figure it is cost of foam board, labor
to cut , install & attach plus difficulty of install
vs having foam co just spray.
of course you'd still need to come behind
the foam spray guys to make sure it is all
sealed & equal depth.

just food for thought.

the only time I've done an unvented crawlspace..
it was a doozy! we used the sealed crawlspace
for the supply plenum of the hvac system.
it was one comfortable crawlspace.
builder built it for his girlfriend...then she
dumped him....LOL!
I still hear about that one..but it was a great house!

best of luck.

Look at the earth as an infinite source of water and mold! Of course, on the Gulf of Mexico coast, so is the air.

ionized, ha! I take it also you live on the Gulf. Rotten what happened with that spill.

energy_rater_la: capitol idea of putting foam on exterior when it is dug up.I believe I read you shouldn't put foam both exteriorly and interiorly on below ground walls, as you can trap the water between the two impermable foam layers.

I am going to have our home rim joists close cell foamed. With great help, I just took down decades old sprayed in insulation, dominant component probably FG, but maybe some cellulose in there. It was installed so thick, in a chronically high water vapor environment it was slightly damp in some places and yes, I'm checking the joist ends and the sub-floor out.

There are so many joists with rims, I just can't see me cutting foam board to put in each. I may end up doing it though, depending on cost. I've been reading about closed cell foam pitfalls for odor: it must be mixed well and appropriate for temperature, and it seems one mistake is to not let the first pass cure enought prior to a second pass. The amine's (cat pee like odor) need to be brought to the surface through curing to emit the odor in a transient fashion. I want to get a very experienced company on this and good weather the day they do it. Our crawl spaces are about 3 feet tall.

Btw all: Great Stuff is a fire block, and ignites at 240 degrees F. Wood studs ignite at ~350 F. Won't be using great stuff in those joists or anywhere for that matter. Nice alternative: DAP Fire Stop 10.1-oz. Fire Rated Silicone Sealant

Here is a link that might be useful: Fire Stop sealant

The IRC does not require sealing of cracks and penetrations in residential walls with highly fire-resistant or non-combustible materials except at fire separation walls between units in 2 family dwellings and townhouses.

The code allows a medium combustible seal "At openings around vents, pipes, ducts, cables and wires at ceiling and floor level, with an approved material to resist the free passage of flame and products of combustion. The material filling this annular space shall not be required to meet the ASTM E 136 requirements."

So the intent of the code is not to make the seal highly fire-resistant or non-combustible but to simply impede the passage of flame and smoke in a combustible structure. In a multi-family or commercial building a foam sealant material would have to be tested to at least the fire-resistance rating of the fire barrier assembly it is part of.

If you wish to increase the fire resistance of the walls and floors of your home you should consider increasing the rating of the drywall,etc as well as upgrading the fire stop seals.

Here is a link that might be useful: fire barrier foam sealant

Here is the ICC Evaluation Report that makes Doe Great Stuff Fireblock code compliant for non-fire-resistance-rated partitions in single family residences.

Here is a link that might be useful: ESR-1961

Thanks for both of those Renovator8. Foam products are a new category for me and I'm at the low end of the learning curve. The Dow fire barrier tape was very informative, especially seeing how hard it was to use wool and caulk as a tool.

I just had my crawlspace walls insulated and the 3 vents closed off with insulation. I have insulation on the top floor joints and they covered that with some type of aluminum sheeting. My concern is I have a few dirt areas in the crawlspace that are damp. Does this area need to be vented? Should I get some type of vapor cover for those areas or should the whole area be covered? My concern was the plastic that was on the floor before held moisture and there were "white" areas of "mold"??? so I removed what was originally there.

Hi Carol. Been a few years since this thread surfaced yet wish to give you some direction.

I do suggest you put down that vapor barrier over BOTH the remaining exposed dirt areas and entire floor, as it will cut down on water vapor in the crawl space air. I am not a big fan of full wall encapsulation.

If you are conditioning your crawl space as it sounds, please refer to the article I attached above for suggested cfm interchange for air exchange (or venting so to speak but absent exterior vents). I think you'll be happy without exterior vents open to humidity and bugs. GL.

Carol: You should start a new discussion. You'll get more responses that way, too!

Thanks for the info. I was not really "conditioning" the crawlspace. I was just trying to find out why the upstairs felt so cold in the winter. An energy auditor recommended the insulation and closing of the vents because of the amount of cold air upstairs that he said came up the walls from the crawlspace. He said I did not need vents and did not need to put down a vapor barrier since I did not have problems with water in the crawlspace. I have read and received many different opinions and don't know what to do. Told if vapor barrier not installed correctly, will not be beneficial. thanks. Not sure how to start a new discussion but any help is appreciated.

So do I need someone to install an exhaust fan in the crawlspace? do they require electricity because there isn't any except one light fixture in the crawlspace. HVAC tech said he would not put a grill in the air conditioning duct because it would take away from the efficiency of my air conditioner. He just recommended leaving the crawlspace door open in the summer. Don't understand the reasoning. Maybe I should just reopen one of the three vents that were sealed? So confusing.

Here's how I would approach your situation:

a. Read the great article on conditioning crawl spaces as with removal of the exterior vents, you inadvertently started down this process, which imho, is a good process. Here is the great article: Martin Holiday: http://www.greenbuildingadvisor.com/blogs/dept/musings/building-unvented-crawl-space

b. Lay down the minimum 6 mm water vapor over the crawl floor. I did this myself and it wasn't very hard: Lowes and HD sell it. Just overlap the edges and use the water proof tape, ideally bringing it up the concrete walls 10 inches or so and securing it. If you can't do the later, just lay it all the way to floor-wall junction with no exposed dirt, until you can do it as it (water membrane over all exposed dirt) is like the main pivotal step in controlling humidity of the crawl space. It's all reviewed in above article.

c. Get your HVAC guy back to cut a small 3" or so supply vent circular hole in your metal duct. This plus him connecting a return duct to a floor above the crawl should provide enough air exchange. The numbers of cfm are above. If he truly won't (and he should read Mr. Holloway's article and answer why not) then perhaps you need a new HVAC man as this is established crawl space conditioning components.

Remember that "perfect is the enemy of good enough". It all sounds complicated, but you've already done the hard part: removing the vents, insulating the rims. Now just lay the waterproofing vinyl membrane and try to get some air active exchange through there and you will be way beyond what most crawl space owners have done to ameliorate crawl spaces. Then sit back and take pleasure in your Home Owner accomplishment! Regards, SW.

Sealing crawlspaces and coupling the house to the ground is very often a good move. Without more details about your situation, I can't say for sure. I am very concerned about what you have done, but I am unsure about what you have done. You have insulation between the crawlspace and the floor? There is an associated vapor barrier? If so, I don't think it should be left that way. The crawlspace has to be able to dry to the inside or to the outside. It appears that you might have it sealed off.

If the soil (or concrete?) floor of the crawspace is wet or damp, there is no way to dry it out if you live in a hot humid climate. Venting will only make it worse. You must keep your living space separated from the moisture in the soil and the moisture that condenses on the cool soil from the air. Both sources are plentiful, infinite, sources of water. Plastic on the floor will prevent moisture from migrating from that source. You may still get condensation from warm air flow over the cool plastic.

Your AC contractor is likely wrong about the crawl issues. The local energy rater should be a more informed source for modern ways of dealing with crawlspaces. Can you provide the specific recommendations? If you want to inform yourself there are a couple of starting points that I can suggest. Your state's land grant university likely has extension projects that can be very helpful and specific for your state's climate. It used to be these were home economics departments, but some time ago, many changed their names to things like family and consumer resources, family and consumer science and human ecology. The other place you might look is buildingscience.com.

I live in Baltimore, MD where we do have hot humid summers. The crawlspace was insulated at the recommendation of an energy auditor that said too much cold air was coming from the walls of the crawlspace up to the living area so he recommended closing the vents and insulating the walls. Insulation to the ceiling of the crawlspace was done before and they covered that with some type of silver kraft paper because some of it was hanging down. The energy auditor said I did not need a vapor barrier for the few dirt spots and did not need ventilation since I never had water in the crawlspace. I just know that the two dirt areas are damp. I was told to get vapor barrier by another person. They didn't over the entire floor and didn't seal it and when I noticed moisture and white spots under the plastic, I removed it and don't know whether it is ok with nothing on the ground or whether there needs to be some type of ventilation. I have a crawlspace door to the inside of the house which they said I should leave open in the summer. The HVAC person said he would not cut a vent in the duct work for ventilation because it would take away from the efficiency of the unit and it would be stupid to heat/cool the crawlspace. I just want to know if there is anything else I should do since it is not vented and there are two large dirt areas which are a little damp.

I JUST found out that I have the same problem in my crawl space. There’s not moisture on the vapor barrier, but the dirt underneath it is moist and midlike consistency.