How Many Vents Do I Need for an Open Floor Crawlspace - Building Codes 

Greg. I have a couple of questions. If let's say one wall of the passive vents are obstructed or closed, would that not hamper cross ventilation? Also, how bad is having your drier venting underneath the crawl space? Any formulas to figure out how much water is getting put into the crawl via warm damp air?

I do have more information on the website. www.homebuildingandrepairs.com/ventilation/index.html I am going to have to do more research, before I can offer any assistance on homes using vapor barriers and crawlspaces, but I always enjoy being buttered up with kind words. It's one way to almost guarantee that a question is coming.

You will need to check with your local building authorities or engineer. However with that said, I've cut holes for crawlspace ventilation on almost every project I've ever worked on, even in sheer walls.

@@gregvancom Thank you for the advice.

It will work for the access, but most of the time crawlspace access opening are located inside the building and won't be screened and are usually made of solid materials.

I'd get it looked at! Get a small local termite company that does fungal Treatments. They will be a me to evaluate your home.

How important is cross ventilation? What if some vents are closed or obstructed?

I’m going to encapsulate the crawl space instead

Yes. But that won't do anything for the wood destroying fungus that you most likely have underneath

eric batrez a dehumidifier will be install

I've seen that done, but haven't seen the results of it, for example ten or 20 years after it was done. The best advice I could give would be to contact your local building department for more information, because they might not allow unventilated areas.

gregvancom It’s for my single-family home. And I’m gonna go with what you say. I just opened up the vents and put chicken wire so the animals don’t come in. But I noticed my crawlspace is cold so I must be having an AC leak that leaks into the crawlspace from the opening from the floor boards

Yes, but airtight homes can create other problems. I will be making another video in the future about crawlspaces without natural air ventilation and covered earth, instead of exposed earth like this video.

I love it and you're not the first and won't be the last.

I would love to see where you got your information from about the United States climates where ventilation of a crawlspace in not appropriate, when they are still building homes with crawlspace ventilation.

@@gregvancom just because they are still doing it and it's allowed by code, doesn't mean that it should be done. There are so many reasons why this isn't an appropriate building technique. The problems arise because builders don't treat the crawlspace as either "outside" or "inside". It gets treated as a little bit of both. Builders will insulate it, but not air seal it, resulting in condensation/moisture problems. Or, they'll air seal it, but won't provide any thermal separation, resulting in cold/hot floors that again create a condensing surface. Moderate climates (think Hawaii) could probably get away with doing this because you can leave windows open nearly the entire year, but most of the US is climate zones 4-6 (some areas are even 7/8). Vented crawlspaces in these climates is definitely not advisable.

Venting a crawl space with mechanicals in it is the dumbest idea ever. Cross ventilation was designed before air conditioning. Plenty of science to back up closed and encapsulated crawl spaces over vented. I also say this with 16 years of fixing crawl spaces.

It usually depends on the type construction. If the house can be built about six inches above the surrounding ground level, then a concrete slab will usually work best. Homes higher or with basements usually have crawlspace.