Jump to content

Crawl space Ventilation


Recommended Posts

I had an interesting conversation with an agent today. I had written up a crawl space because all the air vents had been blocked with insulation. I do not inspect for mold, but I did identify that the wood girder was covered in a black substance and the wood was slightly soft. I recommend that the vents be opened (except during freezing weather) and the dirt ground be covered with 6mil plastic to help prevent moisture from coming up from the ground. The ageant said they had a mold guy speak at one of there meetings and he informed them that the vents should always (ALWAYS) be closed, to keep moisture out, and plastic should never be placed in the crawl space because mold grows underneath. I think I'm going to try and find out who this mold guy is and give him a call, I can't believe our recommednations are completly opposite. Am I missing the boat here?

Mark

Download Attachment: icon_photo.gif girder 1.jpg

48.34 KB

Download Attachment: icon_photo.gif girder.jpg

42.4 KB

Link to post
Share on other sites

Hi,

No, you are not missing the boat. There are several things in play. The mold guy might be right if the outside relative humidity in your area is so high in summer that it will migrate into the cooler crawlspace and condense all over everything. However, leaving soil - any soil- uncovered in a crawlspace will result in about 11 gallons of water evaporating out of 1000 s.f. of soil every 24 hours. Close those vents and where does it go?

If the vents are closed and you create a sealed crawlspace, the soil, and the foundation walls, need to be capped and sealed very tightly, and then that space needs to be conditioned and become part of the conditioned space of the home, otherwise you create a petri dish. If the soil is capped properly and the vents are left open, moisture-laden air will migrate into the crawlspace in the summer and probably condense all over everything, if, like I said above, the r.h. in the crawlspace is less than that outside. So, in that circumstance, it might make more sense to close the vents in the summer and open them in the winter when the air is drier.

Properly capping the soil is a key element to that. If the barrier is put down poorly and mold spore does develop beneath the plastic it can spread out onto areas that aren't capped and then mold spore gets airborne and will germinate on mold-friendly areas such as dampened lumber. The barrier has to be sealed at the perimeter and at overlapping joints. Do it right, and the soil beneath becomes completely saturated with all that moisture that's unable to escape and evaporate into the crawlspace and it reaches equilibrium. Do it wrong, and it continues feeding higher levels of moisture into that air 24/7/365 wherever the soil is uncovered.

You need to become better acquainted with the science of this. Go here: http://www.advancedenergy.org/buildings ... wl_spaces/ and download a copy of Closed Crawlspaces - An Introduction to Design, Construction and Performance and you should have no problem debunking Mr. Mold is Gold if you take the time to study the research on this site.

While I'm at it, what the hell is with that plastic on the underside of those joists? That vapor barrier needs to be against the heated floor, not on the underside of the insulation where moisture that's naturally moving through diffusion into that crawlspace will encounter that cold plastic, condense and form a mold farm in the joist bays which have now been turned into petri dishes (Note the stains).

You've got some pretty poorly informed builders in that town by the looks of things.

ONE TEAM - ONE FIGHT!!!

Mike

Link to post
Share on other sites

I had done a similar inspection, on probably the hottest & most humid day this summer. I had done the exterior and roof first, and by the time I got inside I couldn't stop sweating.( I was very nervous when I opened the electrical panel W/ moist hands)

By the time I got to the crawl space, everything was beading with condensation. The client had concerns about the ventilation. There were 6 vents, and I can't remember how many Sq/FT, but according to my calculations, it actually was sufficient venting. I had informed the client that it was an extreme humid day, and the vents only appeared to be insufficient. I recommended to him, that if the condensation remained to be an issue, he could replace a couple vents with power vents, and that could help with the air flow. I also recommended a dehumidifier since the crawl space was very accessible, and had electrical, and a sump relatively close to the entrance. Do you think these were good recommendations, or what else could I have recommended?

Link to post
Share on other sites
Originally posted by fqp25

I had done a similar inspection, on probably the hottest & most humid day this summer. . .

. . . By the time I got to the crawl space, everything was beading with condensation. . .

. . . according to my calculations, it actually was sufficient venting. I had informed the client that it was an extreme humid day, and the vents only appeared to be insufficient. I recommended to him, that if the condensation remained to be an issue, he could replace a couple vents with power vents, and that could help with the air flow.

Adding more moist air to the crawlspace will make things worse, not better.

I also recommended a dehumidifier since the crawl space was very accessible, and had electrical, and a sump relatively close to the entrance. Do you think these were good recommendations, or what else could I have recommended?

I think they were lousy recommendations. The dehumidifier will never keep up with the moisture-laden air that'll come in through all of those vents. It's like telling the little Dutch boy to poke more holes in the dike then start bailing with a teaspoon.

Try going to the Advanced Energy site that Mike linked to in his post above. Read about how crawlspaces and moisture work.

- Jim, Oregon

Link to post
Share on other sites

De-humidifiers can only hope to work properly if installed in a properly sealed crawl space, set on a humidistat, and monitored regularly. By sealed, I mean insulated vents, 110% lapped vapor barrier run up the foundation wall and mastic sealed. No air in. No exposed ground. It's a piece of mechanical equipment too. So it will impact utility consumption the worse it is installed.

Jeff Mathis

Link to post
Share on other sites
  • 1 month later...

There are mold and termite guys running around the charlotte, nc area telling people to close foundation vents to keep humid air out. Well, unless crawl floor and foundation walls are sealed and I mean sealed, disaster occures after a few summers. When I walk the perimeter and see closed vents, I know trouble is coming. Mold, rot, fallen insulation. It is true we get high moisture readings during humid weather, but it is not enough or prolonged enough to cause any damage. A properly ventilated crawl with a decent vapor barrier and no abnormal moisture entry due to grading or footer drain problems is best left to ventilate naturally during the year with all vents open. Now, properly bulit closed crawl spaces are a whole nother matter and are great if done right.

Link to post
Share on other sites

I recommend the vents be closed in winter to help prevent water lines from freezing. In most homes, especially older ones the water pipes are not insulated and the temps drop down to single digets in my area (I know folks North of Saint Louis will laugh at that). Last winter I left one vent open, even though my pipes are insulated they froze and it took me the entire !@# day of hanging 100 watt light bulbs and hair dryers and cusing to unfreeze them. As far as closing them during the hot and humid daze of summer, I agree with PI, keep them open.

Link to post
Share on other sites

Well, I think this will be a controversial topic for years to come at least in our part of the country.

We recently had a rep from basementsystems.com speak at our pest seminar. Unfortunately, the original speaker had to cancel at the last minute and this guy pinch-hitted. It ended up being more of a sales presentation than a good education / conversation on moisture in crawl spaces.

Regardless, this specific company is heavily marketing sealed crawl spaces. He was really fighting an upstream battle during this seminar with the local crowd.

Crawl spaces here in the northwest have been vented for decades. Yes, I discover problems frequently, but for the most part, the vented systems usually perform well. I cannot submit to a blanket endorsement that all crawls need to be sealed.

This is defintely a case of an entrepeneurial capitalist potentially driving a buiding design change. The repeated mantra from this "speaker" was to contact our local officials and get all the codes changed!! Every crawl space in America needs to be sealed or we're all gonna die!!!! Well, at least that's what it sounded like during the seminar.

And to make matters more complicated I saw at least one if not two 'Basement Systems' trucks in the parking lot (whaddya know, its a franchise opportunity . . .) So, they obviously have a presence here in our backyard. Let the games begin!!

Link to post
Share on other sites

Hi Randy,

Yeah, I agree, the sealed crawlspace crowd can get pretty wound up. However, I've looked at some sealed crawlspaces here in the Northwest and they were nice dry places without any dank odor. Nice to inspect and free of any nasty rodents.

Every time I crawl through a 24inch deep space on my elbows and knees and have to pass over fields of rodent excreta and the tell-tale carcass (Like I did yesterday beneath a 5800 sf 8-plex) I tell myself to get out of this gig and start another company cleaning them out and sealing them.

OT - OF!!!

M.

Link to post
Share on other sites

Does anyone know if there is an actual designation for zoning humid areas in the U.S.? (Like they do for temp climate zones)

Would anyone say: "Any area within the US would call for sealed crawlspaces due to seasonal humidity."

Here in central Illinois, I'm still seeing new developments going up where they are still venting new crawlspaces. (If they don't just throw a house on a slab)

Link to post
Share on other sites

Hi,

I think the bottom line is that a properly sealed crawlspace can be used anywhere, whereas a vented crawlspace cannot. Even in the areas where vented crawlspaces are the norm and work fine when done well, there is so much variation in the quality of installation that the only way you can be sure they are working properly, when a house is new, is to go into and inspect the entire crawlspace at least twice a year for the first few years, just to make sure that things are working well.

On older homes, it's a crapshoot. One would generally expect that if a home is older that the crawlspace ventilation has been working fine. Otherwise, the homeowners would be aware of issues caused by inadequate ventilation. I've found that just isn't true. More often than not, when issues are discovered, they've gone on for decades without anyone knowing about them, and then, when we bring it to their attention, the homeowners will shoot the messenger and declare that we don't know what we're talking about.

We could avoid all of that by just going to fully-sealed crawlspaces and turning them into conditioned space.

ONE TEAM - ONE FIGHT!!!

Mike

Link to post
Share on other sites
Originally posted by hausdok

. . . I tell myself to get out of this gig and start another company cleaning them out and sealing them.

OT - OF!!!

M.

Now c'mon Mike, that doesn't make sense. Right now all you have to do is look at them. Do you really want to spend all that time actually workingin them?[:-weepn]

Link to post
Share on other sites

Ummm,

Well, lemme see. Fight traffic for an hour or more to get 20 miles to spend the next 3-5 hours walking and talking with clients and then fight traffic all the way home and then spend a bunch of time writing my report before sending it off. Then carrying a ton of liability im perpetuity.

All of that for not much more than laborer's wages after taxes and overhead, versus Charging between $4000 and $5000 for two days work with two laborer-wage helpers at a material cost of probably less than $300, unless there's a sump pump installed, plus some tipping fees, cost of fuel, etc.

Gosh, it's so hard to decide.

OT - OF!!!

M.

Link to post
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

×
×
  • Create New...