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Sealing up foundation vents?


Whitenack's Avatar
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05-08-12, 01:49 PM   #1 (permalink)  
Sealing up foundation vents?

It seems like "conventional wisdom" is changing out there to the point where it is no longer recommended to install foundation vents around your house. Evidently, thinking that the vents increased air circulation and therefore helped dry things out, all they do is allow the humid air in. I live in KY, so humidity can be a huge problem during the summer months.

What do you guys think?

I have a house that already has foundation vents. How would you guys propose to seal them up? What would you use?

 
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05-08-12, 04:36 PM   #2 (permalink)  
I am not an expert is this area, but sealing up crawl spaces without sealing the crawl space, allows moisture into the space with no where to go. The result is mold, rot, etc. I don't think you can seal a crawl space well enough to say there will be no more moisture. I say, keep the vents!!

 
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05-08-12, 05:00 PM   #3 (permalink)  
whitenack, you have reopened a pandora's box of comments that will leave you scratching your head. In certain areas of the country, sealing up the crawl, and air condition it is the fad. I say "fad" because it doesn't address the problem sensibly, IMO. I am of the same opinion as JustBill. However, I live in the south and we must, under our codes install foundation venting. The vents introduce and expel air, and it doesn't get stale, moldy, wet, etc.
Who wants to air condition their unused crawlspace, anyway??
OK, Airman, you're at bat!!!

 
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05-08-12, 05:53 PM   #4 (permalink)  
Are there radon concentrations in Kentucky? Crawlspace ventilation is one way to prevent buildup inside your home. Point is, don't start changing things willy nilly without examining all the possible consequences.

 
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05-08-12, 06:34 PM   #5 (permalink)  
The codes are old and outdated regarding crawlspace venting. IMO all crawls will not be vented in the very near future. Many states have already changed their codes and new construction does not include vents.


I sealed my vents up along time ago. I did not put A/C down there but I have 16 ft of baseboard down there to warm it in the winter. Warm it so the floors are warm. The humidity is actually lower in the winter.

Read this. And its 4 yrs old.

http://www.advancedenergy.org/buildi...cle - 2005.pdf

And read this. There are links for more info on this. And a video below from one of the links.

http://www.advancedenergy.org/buildi...ot To Vent.pdf


Watch this video.

http://www.advancedenergy.org/buildi...ot To Vent.wmv

There is a lot more info out there and I studied this intensly some years ago. This thinking is almost 10 years old already.

It would be foolish not to close up your crawl IMO.

Mike NJ

 
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05-08-12, 06:40 PM   #6 (permalink)  
Haha Chandler, looks like you are right. tldoug, yes, high concentrations of radon (even outdoors). Hadn't thought about that. This is good discussion. Thanks.

 
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05-08-12, 07:40 PM   #7 (permalink)  
What are you doing for the radon now???

You can still close the crawl vents but you need the proper radon mitigation.

Basically you seal the floor of the crawl and suck the air out of the dirt with a fan to the outside.

Mike NJ

 
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05-08-12, 08:21 PM   #8 (permalink)  
Washington State Energy Code allows for sealing a crawlspace BUT if done it also requires that the crawlspace become part of the "conditioned" area of the home. That means a vapor barrier meeting minimal standards over the entire "floor" of the space and up the sides of the footing/foundation walls AND both supply and return air ducts to cause an air change of specified amount (I forget the figures) of conditioned (either heated or cooled depending on the season) at all times.

Builders here are not rushing to meet these requirements and are still installing vents under the state (and local) building codes. Then again, our climate, at least in the Puget Sound basin is fairly mild.

As for the smell issue...I have lots of vents in my crawlspace and it stinks to high heaven down there. I'm going to add a couple of small fans to try to get a positive airflow through the place until I can get a contractor to do a clean up and seal job.

 
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05-09-12, 04:38 AM   #9 (permalink)  
The only problem I see with all the "studies" is they are total gross averaging of situations that only exist in certain parts of the country. There is no way any study can encapsulate every situation in a blanket solution. I don't put much credence in jumping on a bandwagon that doesn't have a horse that knows where he is going.
I will agree there are situations where encapsulation of the crawl is a good idea. Take Furd's situation, although a mild climate, I am sure the "Sound" is pretty moisture laden most of the time. Arizona.....moisture, not hardly. So how do they come to such conclusions?
Take it one situation at a time, do what is necssary and prudent.

 
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05-09-12, 08:00 AM   #10 (permalink)  
And just to throw this into the mix....

I helped a woman build her house in VA after the old one was destroyed by a hurricane (Isabel?).

She was required to put in flood vents even though (get this) the house was 10' above ground with 2 16' garage doors in the parking area under the house. One faced the bay...one faced the land. During predicted bad storms she opened the doors about 6 inches. She still had to install flood vents every 6 ft in the block walls, but they didn't require them on the garage doors.

Her A/C and emergency generator also had to be placed on a 10" platform.....but her main panel was in the garage at standard height. So even if she was able to weather a storm and flooding, her main panel would have been flooded anyway.

And lets not forget the hot roof vs vented attics.

Guess what I'm saying is building practices and codes can be funny things.


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05-14-12, 01:57 PM   #11 (permalink)  
Thanks for the comments guys. Let me switch gears, then, (unless I should start a new thread) and ask about the opposite. Asside from cutting more vents into the foundation, how is the best way to dry things out? I have currently have a 70 pint dehumidifier running nonstop. The area is probably too big for just the one, though. The humidity runs in the 50-60 range. Is this good enough or should I keep trying to lower it?

Locations for new vents are limited. The northeast, north, north west and most of the west portions of the house are blocked by diveways, porches, etc. The east, and south area are avaliable. More vents in this area might help this particular area, but not the rest of the house. Do they make circulation/exhaust fans for such a need? Or, again, is 50-60 humidity good enough? And should I start a new thread?

 
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05-14-12, 02:43 PM   #12 (permalink)  
No, this thread is fine. What is the RH outside? You probably won't get is much lower than ambient and I think in KY, 50 is about where you are this time of year, not sure. Don't add vents in an unbalanced manner. Same number on each reveal (EW and NS)

 
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05-14-12, 03:00 PM   #13 (permalink)  
Winter and early spring aren't too bad in our area, but Summer and fall the RH can be bad. Especially late July and August, humidity can get up there and stay up there. Looking at historical averages, most websites say our monthly humidities are 80 in the morning and 50 in the afternoon, throughout the year. Although, that 50 seems a little low.

 
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05-14-12, 03:03 PM   #14 (permalink)  
Heck Chandler, I just saw that you are from GA. I'm not telling you anything you don't already know.

 
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05-14-12, 03:57 PM   #15 (permalink)  
That's why I was suggesting checking what the RH was ambient. I'm from the mountains, so our RH is a little lower, along with temps that the big city or further south. The reason we are required to install equal vents on each side is to keep the pass through wind/air from stalling out. If you are getting mold on joists, it may help to give the circulation a hand with a vent fan of sorts. You didn't indicate a terrible amount of mold on joisting.

 
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05-14-12, 07:31 PM   #16 (permalink)  
Yeah, I don't have mold that I can tell, although I haven't been everywhere under there. TWC says the current RH is 87 right now, but my little cheap hyrometer says it is 63 outside my back door. The same hygrometer gets the same reading in my basement. Soo...that's as good as I can expect to get? Is there any good to running a 70 pint dehumid. in a 2000 sq foot basement? Especially if I have open vents to the humid air outside, I can't imagine that thing will make an impact.

 
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05-15-12, 04:03 AM   #17 (permalink)  
Contrary to the modern vent/nonvent arguments I believe if the ambient RH and the RH of the crawl are close to each other, and the air is moving, you shouldn't have a problem. A problem will arise if any of the air if blocked, gets stagnant, then you get mold.

 
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05-15-12, 08:16 AM   #18 (permalink)  
Thanks for the comments. Since I only have vents on one side with no option of any on the other side, what do you suggest, fans to circulate the air?

 
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05-15-12, 12:51 PM   #19 (permalink)  
Having vents while running a dehumidfier is a problem. It's the same as an open window. I find 50-60% RH to be good. That's where I try to hold my basement. What is the current temperature in the basement? The colder the air, the more difficult it is to remove humidity.

Are you having any problems caused by moisture in the basement? Is there mold growing on your framing? Condensation forming?

Is there insulation in the floor framing above?

You will get mold if the surface temperatures in the crawlspace are below the dew point of the air. An equal RH between outside and inside isn't going to matter. You can have the same RH with different air temps.

 
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05-15-12, 01:21 PM   #20 (permalink)  
Current temperature in the basement is low 70's, about the same as the outdoor temp. No problems caused by moisture that I can tell. No mold visable in places I have been, but I haven't been everywhere. When we first bought the house, there was quite a bit of condensation on the uninsulated ductwork in the summer. I got a dehumidifier which took care of that, plus I've got an HVAC guy coming this month to wrap the ducts.

yes to insulation in the floor framing.

Current dew point according to TWC is 58, which it might get down to outside tonight, but it won't be that cold in the basement.

 
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05-15-12, 02:44 PM   #21 (permalink)  
I don't have a crawlspace so I am not up on all the info, but buildingscience.com has several articles on them. If owned your house I would read up on them and make a decision. Personally, I would rather have control over that space than to leave it up to nature. You are already running a dehumidifier. It doesn't make much sense to have openings to the outside to do so.

The dew point is going to change when the weather gets hotter. Keep that in mind. Those ducts definitely need to be insulated to prevent condensation.

 
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05-16-12, 08:47 AM   #22 (permalink)  
Just to add my 2 cants, I had my crawlspace vents sealed up. Not because of humidity or mold, but because we had water pouring - and I mean pouring - into the crawlspace during heavy rainfalls. And we had a few heavy rains in the Chicagoland area in 2008 when we first moved into this house. Landscaping was above the vents and water had no where else to go. The quickest and easiest thing to do was close them up before we went crazy from all the bailing and shop-vaccing.

My foundation is poured concrete, and what they did was brick up the openings from the inside and cover them with concrete. Then they covered the ones they could reach from outside with concrete. The deck was built over one of the vents.

The crawlspace has a concrete floor so I don't have any problems with moisture. The humidity stays between 50-60% throughout the year. There is a supply vent down there which I have cracked open, but right now thee is no return. It's not cold down there at all in the winter so it doesn't make the floors cold.

 
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05-17-12, 12:15 PM   #23 (permalink)  
I find it bizarre that some of the pros here leave their crawl space vents open. With what we know today, venting crawl spaces is just old thinking. Its an oldtimer thing IMO. Its just stuck in everyone's head that's over 60 I would assume from what I have seen.

Just think what you do in your own home an a hot day in the morning. You leave the windows closed and blinds draped. The house is cool from the night temps with low humidity. What your doing is trying to keep the humidity out as long as you can with this method I am sure everyone has experienced.

Why in the world would you open a crawl space vent to let in hot and humid air?

Plus all the tests that have been done in SC homes per my links.

Oh well I just had the urge to reply.

Mike NJ

 
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05-17-12, 04:04 PM   #24 (permalink)  
Its an oldtimer thing IMO
Guilty.

Why in the world would you open a crawl space vent to let in hot and humid air?
Why in the world would you close up a perfectly good breathing crawlspace to trap hot humid air inside?

Building Science makes for good reading, but it cannot, I dare say it doesn't apply to every region of the country (ies). There is no steadfast rule of thumb. In some areas it, IMO, would be mandatory, while in others...why?
I sealed up one as a subcontractor once, against my better wishes, did everything according to specifications given, sealed up everything but the light bulb (not literally). I heard the contractor had to go back several times and deal with a river of condensate from all the A/C ducts that weren't properly insulated. Talk about mold???
And why would you want to air condition a space that has no one living in it, and NOT have a return? Why would you want to return the air from a crawlspace? It just isn't making any sense to follow along like lemmings without questioning things.

 
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05-17-12, 04:37 PM   #25 (permalink)  
Running a/c sounds stupid to me too. You should be using a dehumidfier in that space.

 
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