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Old 10-30-2018, 10:30 PM   #1
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Vented Crawlspace 101


According to one of the articles in the greenbuildingadvisor.com website, an insulated and vented crawlspace is the way to go if you live in dry plAces. They took some place in Arizona as an example. I checked their stats and we get less rain, less snow and humidity levels are very comparable. Central Oregon zona 6(a), AKA the High Desert.

Can someone please confirm this is the way to go here? Nice R38 batts and lots of vents in the crawlspace?

Cheers.
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Old 10-30-2018, 10:38 PM   #2
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Re: Vented Crawlspace 101


Where I live the crawlspace is 48" below the joist with a 2" skim coat of concrete over 6 mil poly sealed to the foundation. With a perimeter drain around the outside with a water proofing on the out side of the foundation.
Most people spend a few extra dollars and call it a basement.
Rule will be different in different areas.
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Old 11-01-2018, 11:35 PM   #3
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Re: Vented Crawlspace 101


There are generally two ways to deal with a crawlspace:
1. Insulate the walls, seal from the outside and open to the conditioned air of the house
2. Insulate the ceiling, seal from the house and open to outside air

1. is generally the way it's done in northern climates while 2. is much more common in the south. While 1. means you're heating and cooling more cubic feet, it keeps the floor above the crawlspace warmer. Both methods will have a vapor barrier over the floor.
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Old 11-02-2018, 10:44 AM   #4
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Re: Vented Crawlspace 101


What does seal from the house mean? It is very dry here and I believe nobody uses vapor barriers in crawl spaces.
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Old 11-02-2018, 06:53 PM   #5
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Re: Vented Crawlspace 101


Seal from the house means you keep the house air and the crawlspace air separate; it's as if the crawlspace is considered outside the house.
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Old 11-03-2018, 08:32 AM   #6
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Re: Vented Crawlspace 101


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Originally Posted by Richard Pryor View Post
Can someone please confirm this is the way to go here? Nice R38 batts and lots of vents in the crawlspace?

Cheers.
You also need to be mindful of Radon gas issues. Have you checked for Radon?

I talked to a local "Radon Mitigation" guy and he instructed us to seal up all the vents except one, and install this in the remaining vent opening...

https://shop.tjernlund.com/products/...entilation-fan
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Last edited by HenryMac; 11-03-2018 at 08:35 AM.
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Old 11-03-2018, 08:43 AM   #7
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Re: Vented Crawlspace 101


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Originally Posted by HenryMac View Post
You also need to be mindful of Radon gas issues. Have you checked for Radon?

I talked to a local "Radon Mitigation" guy and he instructed us to seal up all the vents except one, and install this in the remaining vent opening...

https://shop.tjernlund.com/products/...entilation-fan
Would you pay extra attention to sealing the floor so house air does not leak into the space?
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Old 11-03-2018, 03:53 PM   #8
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Re: Vented Crawlspace 101


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Would you pay extra attention to sealing the floor so house air does not leak into the space?
Opinions vary, as do radon levels.

The radon test we did showed levels just barely above the "Government Recommended Level".

We've got a new radon test underway now that the fan is installed. We'll see if the local expert knows his stuff.

Worth noting: It is very arid here, we have cactus growing in the yard. So moisture isn't an issue in our crawl space.

Did I mention I hate crawl spaces?
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Old 11-03-2018, 04:00 PM   #9
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Re: Vented Crawlspace 101


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Opinions vary, as do radon levels.

The radon test we did showed levels just barely above the "Government Recommended Level".

We've got a new radon test underway now that the fan is installed. We'll see if the local expert knows his stuff.

Worth noting: It is very arid here, we have cactus growing in the yard. So moisture isn't an issue in our crawl space.

Did I mention I hate crawl spaces?
We don't have radon so limited knowledge there.
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Old 11-04-2018, 06:29 PM   #10
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Re: Vented Crawlspace 101


So sealing the floor is a must no matter where you live?

I don't think anyone around here seals the floor and everyone just insulates floor and vents them. So dry here that no problems seem to arise. But I want to do things 100% right.
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Old 11-04-2018, 09:13 PM   #11
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Re: Vented Crawlspace 101


Do you need a crawl space? You could just build on an insulated slab.
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Old 11-04-2018, 09:16 PM   #12
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Re: Vented Crawlspace 101


That was the plan but the architect drew plans with a crawlspace so I'm stuck with it now. Although I don't think they're that bad in this part of the USA.
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Old 04-23-2019, 05:10 PM   #13
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Re: Vented Crawlspace 101


Quote:
Originally Posted by HenryMac View Post
Opinions vary, as do radon levels.

The radon test we did showed levels just barely above the "Government Recommended Level".

We've got a new radon test underway now that the fan is installed. We'll see if the local expert knows his stuff.

Worth noting: It is very arid here, we have cactus growing in the yard. So moisture isn't an issue in our crawl space.

Did I mention I hate crawl spaces?
Update 2019-04-23

We got our long term 6 month radon test back from the lab. The reading went from 7 pCi/L before the fan installation, down to 0.5 pCi/Lafter the fan installation.

4 pCi/L is the EPA action level.

I knew the fan would help... but wow, that's impressive.
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