Unvented Crawl Space Requires Mech. Venting?

[kwschumm]

We're having a home built with an encapsulated crawl space.

I was reading through the building codes and it says the unvented crawl space requires a vent (see attached). We are already installing a radon mitigation system and a dehumidifier down there. Can anyone see a good reason mechanical venting should be required? I don't really want to pay to dehumidify a space vented to the outdoors.

If there is no good reason then I'll have the vent fan put on a switch and keep it shut off.

 

[jeffer949]

Hrmm thats odd. From my experience crawl space professionals say you should have it encapsulated and sealed all outside vents. And to condition the space like you would a basement. and to have a vent connecting the living space to the crawlspace so air can travel between.

 

[Musicinabottle]

Yeah, that don't sound right. I've never done an encapsulated crawl space but have read and researched them when they were first bursting on the scene.

 

[cgrutt]

These guys recommend ventilation and dehumidification https://crawlspaceninja.com/crawl-s...encapsulation-ventilation-questions-answered/

 

[lakeroadster]

I'm thinking that the radon system will have the mechanical vent... it's part of their system. Just give the specification to the radon folks and make sure their system has the capacity specified.

You're good to go.

 

[kwschumm]

These guys recommend ventilation and dehumidification https://crawlspaceninja.com/crawl-s...encapsulation-ventilation-questions-answered/

I watched the video and thought they installed the mechanical vent fan after the customer complained about dank smells. Since it was a retrofit installation, and had mold growing on the joists in the basement already, it's likely that the smell problem never went away. Perhaps in a new sealed crawl build it wouldn't get that bad in the first place.

 

[cgrutt]

I watched the video and thought they installed the mechanical vent fan after the customer complained about dank smells. Since it was a retrofit installation, and had mold growing on the joists in the basement already, it's likely that the smell problem never went away. Perhaps in a new sealed crawl build it wouldn't get that bad in the first place.

I wasn't talking about the video, in the Q&A they recommend having both ventilation and dehumidifier. They say block off all vents but one.

 

[kwschumm]

I wasn't talking about the video, in the Q&A they recommend having both ventilation and dehumidifier. They say block off all vents but one.

That says they recommend a sealed crawlspace in most cases, but they go on to say that adding ventilation is an option if it gets too humid.

Extrapolating here, my interpretation is that it says that ventilation is an option if humidity is not managed. With a properly working and sized dehumidifier it should never get too humid, ergo there would be no need for the ventilation option.

Perhaps the regs here assume that sealed crawl spaces won't have dehumidification.

 

[tomroblee]

I found an interesting article on the subject,

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

What kind of dehumidifier are you planning on using? I ask because I'm not familiar with dehumidifiers that will operate in cool temperatures.

 

[mrpizza]

If its properly encapsulated, you wont need a dehumidifer. You also don't want to draw air from outside into the crawl, that defeats the purpose.

 

[yeldogt]

I think part of the code is missing. You need the vent or the ductwork. It not the same as a sealed attic. An exhaust vent is pulling conditioned air from the house through the crawl and out -- dumb. Also -- this creates negative pressure. Best to incorporate the crawl into the HVAC system (no returns) adding conditioned air will provide the benefits w/o depressurizing the house.