Crawl space questions

[JStructsteel]

A couple questions when designing for a crawl space.

1. Do you usually take the footing below the frost depth on the inside of the crawi space around the perimeter, also interior piers?

2. What is a min height below joists?

Residential in Ohio.

Thanks

 

[milkshakelake]

1. Around the perimeter, should be at frost depth per code. Frost heave doesn't care if it's a crawl space or not. Water gets under the footing and expands, which pushes it up and cracks the walls.
About interior piers, if the wall isn't waterproofed, I'd put the piers at frost depth. If it's waterproofed, you can put it at a good soil level. I have yet to see a waterproofed crawl space in my neck of the woods, so I'd put it at frost depth.

 

[XR250]

i think code allows 18" w/o using pt lumber (12" under beams).
I would not go any less than 30" below the joists though or there will be some angry subs and homeowners hunting you down.
My house is 30" below joists and 22" below the W8 dropped beams and it is about the lowest I feel is comfortable.

 

[JStructsteel]

Thanks all

I thought that the interior could be higher than Grade due to less water towards the center.

I would expect 3’ would be a good number under joists, a little less at the beam line due to their depth.

 

[phamENG]

I thought that the interior could be higher than Grindr due to less water towards the center.

Grindr? Really?

I'm going to assume you meant grade. And in that case, I agree, the interior should be higher than the lowest exterior grade to prevent a buildup of water in the crawl space. In flood prone areas, FEMA recommends a minimum of 1" higher in the crawl space.

Can't speak to frost depth since to put it above frost depth here would be to expose it above the soil. I agree with XR regarding framing heights. Few things worse than having to tunnel under a beam and getting stuck...just glad there were no snakes in that one!

 

[DoubleStud]

Frost depth at the exterior, not from the interior grade.

 

[JStructsteel]

Thanks again all.

Looks like 18" is the min to joists without having to use pressure treated. I have asked the Building official if they have a requirement.

I would be lower than frost measured from the exterior. About even with the interior.

 

[KootK]

I have yet to see a waterproofed crawl space in my neck of the woods, so I'd put it at frost depth.

Ditto. The nature of ground water movement is that I've no expectation whatsoever that an exterior foundation would meaningfully prevent water migration to the interior of the floor plan. If the interior footings get cold, I think that they may be susceptible to frost heave.