View Full Version : Crawl space dirt level?

Ken Platt
07-20-2018, 4:26 PM
Folks -

I am working in a crawl space with a dirt floor; the main purpose of being under there is to replace the under-floor fiberglass insulation that was infested with mice (stench of urine worse than any outhouse I've ever been in!) .

Anyhow, the dirt floor isn't level. In one corner - about a 5' x 5 ' portion - the floor dirt is ramps up, to just below the level of the top of the foundation. The sill plate does appear to be pressure treated, as of course it should be, but nothing surprises me anymore in this house. Still, it seems as though the floor ought to be level, and at least a few inches down from the top of the foundation. Does anyone know a standard, or practice, for this? I searched online but couldn't find anything on this.

I can remove the dirt, of course, but that's going to be hard and unpleasant. It'd be a lot easier to rake out the elevated portion and spread it over the rest of the crawl space - but I don't know how high I can raise the dirt level with respect to the foundation in the rest of the crawl space. I, and my middle-aged back, are appreciative of any thoughts or information.

As an aside, does anyone know what whitish material might have been put on the soil under the crawl space? There is a lot of white, crumbly, granular material in this area. It looks like that white stuff they put in potting soil, I think to hold moisture, but that doesn't make any sense. Appearance could also be lime, but again, why? I'm worried it's something toxic - especially since I'm going to be messing with that dirt and, like I said, lots of weirdness in this house.

Much appreciated -


Jim Becker
07-20-2018, 5:03 PM
I doubt there is any kind of universal "standard", per say, relative to how even a dirt floor has to be and as you have found, there can be a lot of variation, especially dependent on when construction occurred. It gets covered up fast and sometimes contractors, get lazy. I have that in this house with the exception of our 2008 addition where the township demanded 4' depth and a rat-slab be poured. (The local township has a penchant for being, um...demanding) But the area under the 1980s addition put on by a previous owner varies in level, has a dirt floor and also features a lot of debris that are really fun to crawl over and around. The area under the 1950s construction is even worse...it varies between about 4' at the front and 4" at the back in some places, and yes, that's caused issues with insects over time.

Pat Barry
07-20-2018, 5:55 PM
Ive got the same problem at my cabin except nothing is pressure treated. it's all old logs. At least the logs sit on concrete posts and are dry. I'm working on raking the high areas down and trying to create some airspace. I'd also like to know how much clearance i need.

Dimitrios Fradelakis
07-20-2018, 6:04 PM
A quick Google search turned up these results:

https://www.google.com/search?source=hp&ei=a1tSW_rSBsiv_Qa096fgDg&q=crawl+space+dirt+height&oq=crawl+space+dirt+he&gs_l=psy-ab.1.2.33i22i29i30l10.13.6867..9000...0.0...184.14 53.16j2......0....1..gws-wiz.......0j0i131j0i22i30.VsvSalBVwwY


Tom M King
07-20-2018, 6:21 PM
You don't want it to be lower than the ground level right outside the foundation, unless there is a waterproofed "French Drain" system. Some of the old houses I work on are impossible to even get under.

At least sitting room, without having to bend your neck, is the minimum I would want.

If it's close under there, wear a hard hat, or at least a baseball batting helmet. If you wear a regular cap with a bill, you are guaranteed to hit your head harder than you might think. Even a bare head, without the bill of a cap to block vision, will get hurt more easily than you might expect.

Bill Dufour
07-20-2018, 6:45 PM
Depends on local inspector and ground moisture. I have seen 18" to bottom of floor joist and 12" to bottom of beams supporting joists. In California cripple walls went out in the 1950's. My house ,1949, has a trapzoid foundation but no cripple wall. The mudsill was not bolted.
Bill D.

Ed Labadie
07-20-2018, 7:17 PM
The white stuff would be lime, used to keep mold from growing.


Doug Garson
07-20-2018, 7:45 PM
Might also want to wear a respirator especially if you are removing mouse infested insulation.

Stephen Tashiro
07-20-2018, 9:24 PM
As an aside, does anyone know what whitish material might have been put on the soil under the crawl space?

I suggest you post a photo of it.

One possibility is diatomaceous earth as an anti-roach treatment.

Tom M King
07-20-2018, 9:39 PM
It's fairly common to use lime in a crawlspace for several reasons, with the most common being to cut odor.

Ken Platt
07-20-2018, 10:05 PM
Thanks folks. I guess I'll remove some of it, at least to get it somewhat lower, then maybe finish by raking it out. I just can't see leaving the dirt an inch from the top of the foundation - just seems like a bad idea. It'll be slow and tedious, but at least not as nasty as taking down the insulation (for which job I did put on full suit, N95 mask, goggles. I would not have believed how much sweat I could physically produce in that outfit on a hot day. )

The white stuff must be lime, then. It makes sense, it just hadn't occurred to me that it might be used for a crawl space.


Bill Dufour
07-21-2018, 6:58 PM
The white stuff is more then concrete flaking off of joists that were used as forms? I think in my house they used plaster to fill any knotholes in the top layer of the floor boards.
Bill D

Bill Dufour
07-21-2018, 7:00 PM
The white stuff must be lime, then. It makes sense, it just hadn't occurred to me that it might be used for a crawl space.


May be whitewash to prevent insects and mold. Today it can be applied with a tank sprayer or a plaster spray rig.