Deepening a very shallow crawl space?

14 Replies

Does anyone have good or bad experience deepening a crawl space that is so shallow that it doesn't allow for full access to the crawl space and floor joists for inspection?

I have had some termite trouble so this is forcing the issue and I'd like to fully spray for termites thus the idea to dig out the crawl to 16 inches from soil grade to bottom of joists.

Standing by to fill in any needed extra detail...

Thanks for your help!

I should also mention that my biggest concern is water entry into the space since the soil removal to 16 inches below the joists would also place the crawl grade below the grade of the yard by about a foot.

I'm trying to make sure I won't cause a bigger problem by fixing this clearance problem.

Aaron - what is the foundation made of, and do you know what type?  Where is the water-table in the area? How is the condition of the foundation?  All of these are pretty important questions... Most foundations (in my area at least) are called "strip footings." This is basically just a block of concrete poured directly into a trench, so that the weight of the house sits directly on "un-disturbed" soil.  If this is the case with your house, then digging the crawl space down is not an issue... as long as you only do it in the center of the space, away from where the foundation is bearing on the un-disturbed soil.  On the other hand, bigger buildings tend to be built on caissons with "grade beams" - so that the building itself sits directly on bedrock.  As long as the bottom level is not a floating slab, you can dig to until the building is sitting on bare rock and not affect its stability.

In terms of water intrusion... this is related to the water table and grade of your yard (and soil type) more than the crawl space elevation.  If you live in an area with a really high water table, so that digging down 6" causes a hole to fill with water, then maybe don't do it.  On the other hand, if your yard drains back toward the house, you will get water intrusion from surface runoff.  In most cases, water does not percolate very quickly through soil, so a normal rain-storm will inundate the top 6" of soil, and then the rest of the water will become surface runoff, going into rivers and eventually to the ocean.  In soils with a high clay content, it can take months or even years for water to percolate even 1" (which is why clay is used to line landfills... keep that trash juice away from me!). 

So I guess the answer is... it depends. Stay away from your foundation and any support columns,  control water, and generally you will be fine.  

Only take out what you need to perform the work stay away from footings and interior columns ,

Use a pump type bug sprayer to spray whatever your spraying 

Hint copper green  

You can dilute with mineral spirits

One to one  

Don't forget to Wear protective clothing,throw away type tyvek suite and the proper respirator.   

Also if you do have active termites forget what you read and hire a fumigator.

Do all repairs through the subfloor and interior walls drywall work is cheap .

Your welcome

Not sure about Virginia but in California many foundations only go down about a foot. As @John Wanberg said don't dig right next to a foundation or post. Also, you might have sewer lines resting on the dirt which will need to be supported after you remove the dirt.

If your water table is only a foot beneath the grade level you would probably either have rotting wood or very good crawl space ventilation.

I can't imagine how removing a foot of dirt from beneath you house would have any affect on surface runoff. If your dirt is almost impervious to water, removing dirt from beneath your house won't change that. If the dirt is as porous as sand, the water sits at the water table height.

@Aaron Z. Wow, this takes me back 35 years ago when I was in High School. One of my dad's old rental houses in Northern CA - Eureka. did not even have enough space to crawl under. It was a small home maybe 1,000 sq ft or so. He and I dug the whole thing out using a 5 gallon bucket and pulling it out with a rope one bucket at a time! Took 6-7 large truckloads out. Jacked up the house, poured new piers and leveled the house out. Strung up some batt insulation and called it a day. Or I should say maybe a month or so! I'll never forget that one! Everything turned out great when we were finished. Never something I would do if it was up to me though.

Originally posted by @John Wanberg :

Aaron - what is the foundation made of, and do you know what type?  Where is the water-table in the area? How is the condition of the foundation?  All of these are pretty important questions... Most foundations (in my area at least) are called "strip footings." This is basically just a block of concrete poured directly into a trench, so that the weight of the house sits directly on "un-disturbed" soil.  If this is the case with your house, then digging the crawl space down is not an issue... as long as you only do it in the center of the space, away from where the foundation is bearing on the un-disturbed soil.  On the other hand, bigger buildings tend to be built on caissons with "grade beams" - so that the building itself sits directly on bedrock.  As long as the bottom level is not a floating slab, you can dig to until the building is sitting on bare rock and not affect its stability.

In terms of water intrusion... this is related to the water table and grade of your yard (and soil type) more than the crawl space elevation.  If you live in an area with a really high water table, so that digging down 6" causes a hole to fill with water, then maybe don't do it.  On the other hand, if your yard drains back toward the house, you will get water intrusion from surface runoff.  In most cases, water does not percolate very quickly through soil, so a normal rain-storm will inundate the top 6" of soil, and then the rest of the water will become surface runoff, going into rivers and eventually to the ocean.  In soils with a high clay content, it can take months or even years for water to percolate even 1" (which is why clay is used to line landfills... keep that trash juice away from me!). 

So I guess the answer is... it depends. Stay away from your foundation and any support columns,  control water, and generally you will be fine.  

Very detailed response.  Thank you.  The footer is poured concrete, not sure if it is original (~100 years old) or to what specs it was poured to, but the standard now is 8 inches deep and 16 inches wide, about 2 feet below grade.  Then there is a course or maybe 2 courses of cinder block on top of that.  The house was fully rehabbed about 12 years ago (down to the studs)...not sure why they didn't jack up the house and add another course of block...probably cutting costs. 

The weight of the house sits on the footing which sits on undisturbed soil.   I haven't been under there but I will definitely have the digging crew avoid getting too close to the footer/block foundation or near any piers that might be under there.  The footprint of the house is pretty small - only 1400sf, 2 story and the house is about 22 feet wide.  

Water table isn't close to the surface, though the house is only 15 feet above sea level and less than 1/2 mile from the water in the inlet to the ocean.  The back yard really doesn't "drain in any direction...it fills up by a few inches when it rains and then just percolates into the ground in a matter of hours.  My fear is that I might be encouraging water to run under the house, but I'm leaning toward believing that won't be an issue...

Thanks again for your feedback.

Originally posted by @Jesse Jesttes :

Only take out what you need to perform the work stay away from footings and interior columns ,

Use a pump type bug sprayer to spray whatever your spraying 

Hint copper green  

You can dilute with mineral spirits

One to one  

Don't forget to Wear protective clothing,throw away type tyvek suite and the proper respirator.   

Also if you do have active termites forget what you read and hire a fumigator.

Do all repairs through the subfloor and interior walls drywall work is cheap .

Your welcome

 Jesse, I've got a termite treatment warranty so I won't be doing that myself, I just want to get him full access to the crawl...honestly i want to know the full condition of the joists as well since there are active termites I'm trying to get rid of.  I'll be sure to spell out the precautions you've spelled out so that he doesn't cause any structural problems by his digging.  Thanks again.

Originally posted by @Jeff Keller :

Not sure about Virginia but in California many foundations only go down about a foot. As @John Wanberg said don't dig right next to a foundation or post. Also, you might have sewer lines resting on the dirt which will need to be supported after you remove the dirt.

If your water table is only a foot beneath the grade level you would probably either have rotting wood or very good crawl space ventilation.

I can't imagine how removing a foot of dirt from beneath you house would have any affect on surface runoff. If your dirt is almost impervious to water, removing dirt from beneath your house won't change that. If the dirt is as porous as sand, the water sits at the water table height.

 Jeff, thanks...that's a good point about any lines or things hidden in the dirt.  I don't think I have to worry about the water table.  Thanks for making me feel better about the water runoff...what you say makes a lot of sense to me, but I didn't want to just go with my gut...it's nice to hear that from a neutral party.

Originally posted by @Charlie Price :

Aaron Z. Wow, this takes me back 35 years ago when I was in High School. One of my dad's old rental houses in Northern CA - Eureka. did not even have enough space to crawl under. It was a small home maybe 1,000 sq ft or so. He and I dug the whole thing out using a 5 gallon bucket and pulling it out with a rope one bucket at a time! Took 6-7 large truckloads out. Jacked up the house, poured new piers and leveled the house out. Strung up some batt insulation and called it a day. Or I should say maybe a month or so! I'll never forget that one! Everything turned out great when we were finished. Never something I would do if it was up to me though.

 Sounds like a good time!  That'll make you appreciate being able to pay someone to do that next time!

Sounds like you really want to jack up or lift the house rather than dig dirt out from under it - should have the same effect of getting more clearance beneath. Have you though of that as an option and priced it? (I have never done either of the above since basements are normal where I am.)

In exactly the same situation I opted to jack up the house as opposed to disturbing the soil. It was easier, quicker and caused no other issues.  Did it myself with 1/2 dozen 20 ton jacks, took about 12 hrs. Raised it 1 ft. It was a small home, about 1000sq ft. but works the same for any size home.

Greg S. That sounds like a fun project...one I'd take on in the future for sure. Right now for this property I doesn't make sense for me to do it... it is occupied and it never has a vacancy. It's 3 hours away from where I live. I work a day job full-time. And I'd want to be on-site to oversee this if I didn't do it myself. It's in the city limits and I don't have any contracting licenses so I'll have to check but I'm not sure how keen they'd be on me doing the work myself. And there are termites now...
I'm counting down until my time isn't more valuable at a desk so I can take on stuff like this myself. I love the hands on, problem solving aspect of RE investing and I enjoy working with my hands and seeing a project from start to finish done right.

@Steve Babiak thanks for the feedback. I'm going to price that out.

After considering my problem more I believe I won't have a water intrusion problem since the entrance and back part of the crawl is already accessible just not with a full 16 inches of clearance and it's always stayed dry. That is the part of the crawl closest to the back yard where the water pools a bit when it rains hard.

Aaron, I am a fellow Virginian (Richmond) in the exact same situation. My house is 100+ years old with an almost inaccessible crawlspace. I'd  like to dig it out so I can get up under it, maybe cap it, insulate it, etc. I am curious how your project went, approx. how much it cost you?  I talked to a structual eng that said he thought I'd be fine as long as I stayed as far away from the structural members as I dug down. I am considering renting a vacuum trailer to suck the dirt out as it's removed. Have you encountered any moisture issues so far? 

Create Lasting Wealth Through Real Estate

Join the millions of people achieving financial freedom through the power of real estate investing

Start here