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Old 04-03-2011, 10:01 PM   #1
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Conditioned Crawlspace question


Since our initial excavation didn't make it seem practical to create a full basement, we are going to go with a crawlspace foundation. I've been researching it for several days and I'm pretty sure I want to do a conditioned crawl space.

I think what I want to do is as shown in Image 10 in this document:
http://www.buildingscience.com/docum...ance-and-codes

I can see why these things are written by PhD's. There is so much to consider that it makes my head spin. But because there is so much information available, it is a bit overwhelming and definitely hard to figure out the real right answer.

I'd like to hear any opinions or experience with doing that but I also have a few questions.

In background, I am in Oklahoma. From a building code region, that is region 3A - no interior vapor barrier required. We just had the lot leveled as a starting point and found that we have a few feet of shale and sandstone and then wet red clay.

So my questions are:

1. What material is used for the capillary break between the footing and the foundation wall? Would I use the same paint- or spray-on material I would use for a basement wall or, in my case, the foundation wall?

2. For soil gas venting, I've seen a product from CertainTeed, Form-A-Drain, but it's not available where I am. But I'd like to create the same effect of an interior drain field connected to the external perimeter drain. How do I pass a pipe through the foundation to tie the two together? My crawl space will be about 80 feet long. How many times should I tie the interior and exterior drains in that much footing?

3. The pictures in the linked pdf don't make it clear, so would you recommend unfaced foam insulation or foil or other facing on the foam? And if faced, facing in our out?

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Old 04-04-2011, 11:44 PM   #2
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Conditioned Crawlspace question


Check with your local B.D. and see if you are able to use a conditioned crawl and if radon is a problem in your area.

Gary

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Old 04-05-2011, 10:00 PM   #3
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Conditioned Crawlspace question


There is no B.D. in the county where I live. The US Government says the average radon for the county I am in is between 2 and 4. We seem to live in a little hot spot.

In any case, the documentation on the conditioned crawlspace recommends a passive system for soil gases. Since the soil gas system also works as a passive radon reduction system then we're probably ok. Between 2 and 4, it seems that a passive mitigation system is the recommended starting place. All we can do is wait and see if we need to turn it into an active system by adding a fan later.
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Old 04-06-2011, 05:16 AM   #4
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Conditioned Crawlspace question


don't get caught up in 'zen' radon stuff,,, 20mm vapor barrier & powered foundation wall vents,,, shut the vents in the winter & just run 1 exhaust vent,,, we usually install 4 - 2 sucking & 2 exhausting - opposing sides.

put 'em on a timer & your annual operating cost will be less than a drive-thru dinner
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Old 04-06-2011, 03:22 PM   #5
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Conditioned Crawlspace question


I would recommend not venting your crawlspace. If your bringing in air, then your bringing in moisture. The polyethelene vapor retarder on the ground will deter any radon. After putting down the plastic, I would suggest pouring a pad of concrete over your plastic. Putting up 2" extruded or expanded foam on the walls with adhesive with your seams taped with tyvek tape or its equivalent should do the trick. Buildingscience.com has a lot of useful information and I have seen some damage done when the crawlspace is vented with the floor cavities insulated with fiberglass insulation.
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Old 04-07-2011, 01:39 PM   #6
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Conditioned Crawlspace question


I'm w/ XX. Condition the crawl space, and deal w/ radon as appropriate for your area.
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Old 04-07-2011, 09:33 PM   #7
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Conditioned Crawlspace question


The building science documentation suggests the vent for soil gases, regardless of radon, with a conditioned crawlspace. Nice thing about it is that you get what should be good enough for even most radon situations out of the same passive vent system. Since, from what I have read only, you can't really do a radon test until the house is closed in, we won't know if we need an exhaust in the vent until we're done. Most likely we won't.

Anyway, the idea of having a water drain on both sides of the footings makes a lot of sense to me, considering the clay we'll be building on. So I'm still curious what others have done to connect drainage systems from the inside of the footing to one outside of the footing.

I'm leaning, though, toward just having both drain systems run to open air outside. That requires a penetration through the footing, though. Then there's that whole "relieving arch" thing. But not having an inspection lets me define "relieving arch" my own way.
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Old 04-08-2011, 06:10 AM   #8
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Conditioned Crawlspace question


radon evac systems are very similar to a french drain in detail except for the vertical standpipe into which a fan on a timer is placed - same excavation, same 4" pipe, same 57stone bedding & cover,,, on occasion we would piggyback radon into the water system,,, not difficult at all.

if you don't need a submersible wtr pump due to gravity drainage availability, you'd still need the exhaust fan,,, unsure why you'd want to penetrate the footing when you can place a ' U ' of sched 80 pvc & reinforce the ftg w/moe steel
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Old 04-08-2011, 09:00 PM   #9
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Conditioned Crawlspace question


itsreallyconc, so instead of going through the footing, you're suggesting underneath with a U? That would mean the U would always hold water since it would be the new low point with "up" on both ends, wouldn't it?

That's why I was thinking of going through - in the same way that CertainTeed recommends with their Form-A-Drain; that would mean the interior drain would drain to air through the exterior drain. At least that's my thinking, for whatever that's worth.

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