Crawl Space Vents... Open or Close...?

[BLOWN PONY]

It has always been my understanding that you are to close the vents in the winter and open them in the summer, but after doing some goggling it looks like no one can decide what actually works....
Some say fill them with insulation board and keep them closed year round, others say leave them open unless it's supposed to get extremely cold for a few days.

Yesterday while in my crawl space running some CAT5, I realized my crawl space is extremely damp. Damp to the point that water is pooling on my vapor barrier plastic.
All of the HVAC duct work is literally dripping condensation. Water brings bugs and mice, which bring spiders and snakes, which I could live without... I went around and opened all the vents so I guess I will wait and see if it drys out. After reading some of those articles, I don't feel like it will though.

Also, one of the builders I design homes for has made "Conditioned Crawl Spaces" standard with all his homes and really builds it up like its the best thing in the world. I always figured it was just a selling ploy until now. Anyone living with a conditioned crawl space? Thoughts?

I live in North Carolina, so we get a decent amount of rain and humidity during the summer months...

Any advice, or past experience with this would be greatly appreciated. :beer:

 

[wht93gted]

My old house had the automatic ones. They opened when it got above 70\75 or so, and closed below 40.

So, based on that, I'd assume open in the summer, closed in the winter, generally. We had a high water table, and tons of humidity but still never had dampness issues down there, so I guess that logic works.

Also, I don't know about down where you live, but since the crawlspace isn't heated\cooled, your HVAC ducting most definitely should be insulated (wrapped in some type of foil insulation), and if it's insulated it shouldn't be dripping any condensation.

 

[mnewxcv]

watch out for mold too, though it might not be as big a problem there as it is in MA.

 

[BLOWN PONY]

My old house had the automatic ones. They opened when it got above 70\75 or so, and closed below 40.

So, based on that, I'd assume open in the summer, closed in the winter, generally. We had a high water table, and tons of humidity but still never had dampness issues down there, so I guess that logic works.

Also, I don't know about down where you live, but since the crawlspace isn't heated\cooled, your HVAC ducting most definitely should be insulated (wrapped in some type of foil insulation), and if it's insulated it shouldn't be dripping any condensation.

Yeah, they are wrapped in foil insulation, but it's still building condensation under there.
It's been hotter than hell and we have had some rain recently, so the humidity is pretty high right now.

 

[PSUCOBRA96]

Get a dehumidifier down there and pull out the moisture

 

[ashleyroachclip]

I never close them.
The cooler air acts as a barrier in conjunction with my attic gable vents to keep the warm air in during the winter and cool air in the summer .
The crawl space needs to breath , and can not do so if it is closed up .

 

[Snake Pliskin]

Get a dehumidifier down there and pull out the moisture

Definitely. Same here in SC. After researching the issue my solution was to seal the vents and put a big dehumidifier down there. It was so bad that my floors deformed a bit 2 summers ago. In this part of the country with temps and humidity it is almost never advantageous to open those vents. When the AC runs the duct work cools and forms condensation and allows it to wick up into the flooring near registers and dripping onto the moisture barrier at low points. The moisture is coming through foundation vents not up through the ground. Open crawls spaces are out dated technology. PM me if I can help. Good luck.

 

[wht93gted]

I'm not sure about down there, but we get tons of humidity here, but moisture definitely comes up from the ground.

I could see the moisture under the vapor barrier in my old house. Certain times of year when I'd go into the Crawlspace you could see condensation on the other side of the plastic, since it was just clear. Why do you think cars parked on grass for long periods rust out on the bottom? Ground moisture does it.

I think we had around 8 vents on our 1500 sqft ranch, that were open in the summer. It was always very cool down there. I always assumed my Ac was leaking and cooling the Crawlspace, but I never has condensation issues. Our ducts were the fiber board kind, if that makes a differnence?

Definitely. Same here in SC. After researching the issue my solution was to seal the vents and put a big dehumidifier down there. It was so bad that my floors deformed a bit 2 summers ago. In this part of the country with temps and humidity it is almost never advantageous to open those vents. When the AC runs the duct work cools and forms condensation and allows it to wick up into the flooring near registers and dripping onto the moisture barrier at low points. The moisture is coming through foundation vents not up through the ground. Open crawls spaces are out dated technology. PM me if I can help. Good luck.

 

[coyotehp]

I open them around April and leave them open until December depending how cold it gets around that time. Once the temps start hitting below 30 and staying there, I close all but one that is under the deck. It blocks alot of the wind but still lets some air in. Its good get some fresh air under there as much as possible. I'm close to the va/nc line.

 

[Mr. Mach-ete]

The new building codes here in Maryland require all crawl spaces be encapsulated and conditioned.

We recondition crawl spaces, install heavy duty vapor barrier, seal off the walls and vents, install water management system in the foundation floor and last but not least install a dehumidifier. We revisit our rehab jobs and they are bone dry.

 

[SonicDTR]

It entirely depends on how it is currently setup. Mine is an old setup, with vents to the outside and seperated from the conditioned house environment, but im going to update that soon.

Here is a thread on mine: http://www.workshopaddict.com/forum...t/3198-crawlspace-vapor-barrier-clean-up.html

 

[Snake Pliskin]

+1 This is the proper way to manage crawl space environment.

The new building codes here in Maryland require all crawl spaces be encapsulated and conditioned.

We recondition crawl spaces, install heavy duty vapor barrier, seal off the walls and vents, install water management system in the foundation floor and last but not least install a dehumidifier. We revisit our rehab jobs and they are bone dry.

 

[svtfocus2cobra]

I've done a fair share of crawl space work for custom homes. I've had houses built on clay that didn't drain and ended up with about a foot of water trapped in there. Had to dig trenches to a low point where I dug a two foot deep hole, filled the bottom with concrete and then installed a pump that pumped it under the foundation and tied it into the foundation piping. That place was soaked and that was all I was told to do to remedy it so I think you'll be fine with just a little bit of condensation.

From my understanding, I was always told by the home inspectors that the ground needed to be well covered with the barrier to protect from Radon poisoning I'm pretty sure it was. If that's true then I would think you would want vents open also? We always built them with vents open.

 

[wundrbird]

The new building codes here in Maryland require all crawl spaces be encapsulated and conditioned.

We recondition crawl spaces, install heavy duty vapor barrier, seal off the walls and vents, install water management system in the foundation floor and last but not least install a dehumidifier. We revisit our rehab jobs and they are bone dry.

Definitely this. My wife and I bought a house in September, and it's a bit of a mess on the underside. I've researched techniques to encapsulate, and I look forward to starting this "little" project AFTER snake season.

What dehumidifier would you recommend? My crawl space is around 1700 sq. ft.

 

[Snake Pliskin]

I used a Horizon Galaxy because its equal to its competition but has a 5yr. warranty as opposed to 1 yr. with most other brands. It drains into a condensate pump and piped where I can verify that its working.

 

[Mr. Mach-ete]

Definitely this. My wife and I bought a house in September, and it's a bit of a mess on the underside. I've researched techniques to encapsulate, and I look forward to starting this "little" project AFTER snake season.

What dehumidifier would you recommend? My crawl space is around 1700 sq. ft.

A ninety pint dehumidifier will work just fine, Aprilaire makes a decent free standing dehumidifier.

 

[wvmystichrome]

My old house had the automatic ones. They opened when it got above 70\75 or so, and closed below 40.

So, based on that, I'd assume open in the summer, closed in the winter, generally. We had a high water table, and tons of humidity but still never had dampness issues down there, so I guess that logic works.

Also, I don't know about down where you live, but since the crawlspace isn't heated\cooled, your HVAC ducting most definitely should be insulated (wrapped in some type of foil insulation), and if it's insulated it shouldn't be dripping any condensation.

This is the way mine works also.

 

[Mr. Mach-ete]

There's a problem with keeping vents open, you allow humid air to migrate under your home. Since the crawl floor and duct system are msot likely under the dew point water condenses on every surface. I've been under home where it was raining drops of water from every surface. Sealing off the crawl space and mechanically removing residual humidity is the only solution.

Pro Build sells heavy duty 10 mil plastic which makes an excellent vapor barrier. Another heavy duty vapor barrier is 60mil black roofing membrane. It expensive but it really make for an awesome floor barrier.

You need to seal the foundation walls off too. R-6 fire rated foam board can be attached to the foundation walls with tap cons and stainless fender washers. The gaps can be sealed with expanding foam.

Do these things and you'll notice a huge difference in the environment under your home.

In serious cases we've trenched french drains with 4" corrugated pipe to sump pits. Installed dehumidifiers and had them drain into the sump pits to be discharged outside.

 

[YJSONLY]

I went to a guys house this week who is building his house. We are in Florida and his house is about 3 feet off the ground with a heavy liner that is sealed to the block walls with 2 huge de humidifiers. House is sprayed with foam walls and roof.

They are also have a 16 seer AC unit and will be installing solar panels to "super heat" the freon and "double" the efficiency of AC unit. He said they do this in Europe all the time?.! I'm curious how it turns out. The homeowner is very very mechanically inclined person as he is a aircraft mechanic/inspector for 25+ he is going to run AC as is first to get base line and then hook up solar "super heat freon system" to see savings or lack there of.

 

[alex3610]

My house here in VA has a crawl space with a plastic vapor barrier and foundation vents. First few years I was here I just left the vents open because I really never gave them any thought. I started keeping them closed all the time for two reasons. First thought was that in the winter cold ass air was coming in and my floor was cold to walk on. Second, in the summer, humid air circulates through to the cold/dark crawlspace where it then turns to condensation. I see no real benefit to keeping them open. Fully encapsulating and adding a dehumidifier would be the best way, and that's what I'll do in my next house. I still don't understand why in VA/NC they don't build basements. Seems like the only houses with basements here are built on a hillside and have a walk-out one. Cheap square footage if you ask me. Not to mention great place to stick mechanicals for ease of maintenance.