Discontinuous footer between full basement and garage
Between my garage and full basement there is a ‘crawl space’ that has a sloped grade. I’ve read that it is common in the Northern climates when garage footings don’t need to be as deep and when they are attached to homes with full basements. However, most information I read is on poured concrete walls allowing this footer step up/gap because it can span the load. My house is built on block, with a longer block spanning this gap in the crawl space.
I’ve attached a photo of one side of the crawl space in question. The other side is identical. As you can see, there has been some soil that made its way through those gaps. The exterior soil grade is only about 1-1.5 feet above the gaps opening. My plan is to create a form to pour concrete to seal this gap. part of the bottom half of the block foundation is 4 inches thicker, so I will just line the form right up with that and make a nice clean ledge on both exterior walls. Is this a good technique?
I’m encapsulating the crawlspace, so looking for ways to sure-up the exterior walls and give myself cleaner surfaces to insulate and cover. The slope is a whole other post/issue 🙂
Replies
The Step or "Jump" in footings you see is very common but not as common to see once the foundation is backfilled and crawlspace leveled. The typical reasons of the example you pictured is overzealous excavator, sand, gravel or loamy soil conditions ,change of plans or combination of any and all. No one wanted the additional work or materials required, so the house was delivered without either.
In your case they neglected the additional material to backfill the whole crawl space above the level of the 'Jump' ,including the longer block span you mentioned ( aka: the crawl space foundation wall footing).
Animals ,less likely but water very likely will enter through this gap and leak through the "cross wall" separating the deep basement and crawl space, this water typically confuses homeowners since it is not considered an exterior wall and leaks into the basement during the biggest storms. On a regular basis , especially with sandy soils it is a perfect recipe to loose a teaspoonful at a time and then start seeing the step cracks ( in block) or the wide cracks in a poured wall at the 'Jump'
It is prudent to pour in place a wall below this gap at minimum the same 8" as the CMU to stop additional soil from being displaced. Pour to the existing sloped soil under the crawl space footing and up to to the footing itself from interior or exterior, whichever is easier, just add a birdsmouth/s at the top or a slightly wider wall to make the pour easier on you and vibrate with hammers/sawzall ( no blades) etc
Since your new wall will be below the frost line and as long as its properly pinned to the existing wall and footing you'll be in good shape. If you excavate that 1-1/2' to 2' on the exterior you mentioned you can detail with some of the shallow wall/slab insulation methods in past FHB articles. in case the original overdig was due to loose soil , you may want to form both side to save on concrete and control the process better, remembering that anything below the crawlspace footing you are exposing to form for your pour but not disturbing soil below that level.
Make sure you add draintile to the footing at the base of the crosswall ( crawlspace side) if not already present and tie into your existing system en route to sump pit or daylight
Back fill the rest of the crawlspace with well draining soil and add additional drain tile on the interior perimeter of the crawl if none is present or working on the exterior. Keep in mind Radon mitigation, if needed can typically be tied into the drain tile system, Future vapor barriers with or without a poured concrete slab will be dependent on radon levels, moisture and humidity levels and general comfort.
Check your downspouts with all this in mind, these areas are usually where roof lines, heights and elevations change and concentrate large amounts of water into your area of concern
Good Luck , It's worth doing and can be done in stages as time,budget and back allow.
Thanks for the detailed info. The biggest thing for sure will be taking extra care when digging for my forms up to the garage footer. I actually already added some concrete blocks on the exterior of the gap when I was having a buried oil tank removed that the prior owners shouldn't have buried there lol they ran the oil lines through that gap.
I'd like the space somewhat usable in the future for storage (wine, emergency supplies, and a whole basement dehumidifier), so I'm trying to address the slope in the easiest way right now. Backfill really isn't in the plans, although I plan to put some stone along the crosswall to level it out some more.
I go back and forth on the drain tile. There is evidence of one on the exterior of the home, but def not it great shape. Not a lot of water issues, as the house is on a slope going downhill in the backyard. Because of this, running to daylight would be really difficult, and I just don't see the need to install a sump pump with my walkout basement. The moisture present I'm 80% sure was from bad grading and downspout placement, both have which been addressed. No intrusion all spring and summer and I've got the humidity down 10% on average. We will see with snow melt this winter. Just some efflorescence that seems to be side effect of moisture finally evaporating out of the block. But I do have pause that putting plastic down will cause moisture aggregation underneath without the ability to evaporate into the space above.
Your correct, a vapor barrier directly on top of the existing crawl space grade would be below the problem area and an invitation to collect moisture as noted.
The walkout basement is a blessing for sunlight, drainage and possible access to backfill the crawl space to make it functional space, maybe 8 to9 yards?
Or you can open the cross wall access to the crawl space down to the existing basement floor and build a second parallel cross wall ( retaining wall) at the jump thereby expanding the basement footprint and using the soil to fill in behind the new cross wall.
Spray high density closed cell foam to match existing grade, pour flowable fill, bucket brigade of crushed stone or washed river rock, fill with GeoFoam, build a pressure treated deck ( don't do this). The simplest economics would be finish what the builder 'forgot'.
A few more photos of exterior garage portion and opposite wall with exterior could help others when they weigh in.
I added a few photos and have many more to show the how it typically presents itself and that animals once they find this access think they found the Waldorf Astoria.
Happy Thanksgiving,
Pb
I had thought about the separate retaining wall within the crawl space.. just wasn't sure how'd i go about it. I initially over thought it by drawing up a 3 step method, simply because of the way the dirt is cut. But I think a single wall that runs 1 block higher than the footer gap, just to the right of the gap would actually work pretty well, and be a clean solution.
I don't think I'll expand the opening into the crawlspace, but by having the floor level on the crawlspace side of the crosswall it would def allow for usable space to step into with an attic ladder style latch. Here are some more photos of the exterior side of the vented wall. a before/during/after of the area being cleared, oil tank removed, and back fill with spout extension completed.
I've also added a photo of what I was thinking for the retaining wall. Simply using CMU blocks and mortar, I estimate that will be enough to support the backfill. I need to research a little more as my masonry knowledge is limited beyond paver patios and garden retaining walls. Grey is the wall and gravel. Brown is soil backfill. Everything would be covered with 16mil plastic. I could then pour 3inch concrete in the future with 2 nice flat surfaces.
Edit: dunno why the photos turn when opened up. Also, have a Happy and Blessed Thanksgiving.
Thanks for the addt'l photos.
The existing cross wall between the big basement and the 'little basement' ( aka: crawl space) is a retaining wall. In your case it was either/or:
a. misplaced given the original excavation
b. not completely backfilled
If a., building a new retaining wall farther back, the lowest part of the existing crawl space will be as deep as the basement and require you to use the ladder to get up and another ladder to get down into the original deep crawl space, similar to a dike surrounding oil and gas tanks ( similar to existing set up)
If you finally decide on the new retaining wall it would seem that walk in access would be a key deciding factor. Most contractors would consider removing some block , completing work and reinstall of block cross wall access.
If b., consider the original intent as a crawl space " little basement", then pouring a wall under the original area of concern should give you peace of mind. To capture the space for possible storage then the space should be leveled off so that only one ladder brings you up to the new level.
The new photos show the sidewall vent which can be used for a concrete pump hose for a new cross wall footing. Keep in mind once you cut back the existing slope ( angle of repose) in the crawl the new retaining wall needs to 100% support the soil under existing three foundation walls, this includes the wall construction details, backfill material and placement.
Project discipline:
*The vent could also serve as access to pour lots of gravel to level off the space!
**Is there a similar vent on the opposite wall?
A third of the work
Using gravity to the best advantage
More economical
Great workout vs. Chiropractic visits
Crisp winter weather vs. summer humidity
Plants and landscaping dormant, will come back easy in the spring
Beats watching TV and makes nightly reading more enjoyable
Get some 1/2" plywood for stone delivery, a good wheelbarrow, two dozen bakery surplus buckets and a few crullers, fritters, bear claws or puncskis, some hot coffee and you'll be done by Christmas if you can 'Tom Sawyer' some Thanksgiving guests into helping ( see donuts and coffee)
Merry Christmas,
Pb
Thoughts on laying block on compacted stone? And do you think I'd need to fill the cores of the entire CMU block retaining wall? It'd be approx. 4 feet tall. I'd certainly core the corners where I'm lining up against the exterior walls, and probably the first row of block. I wonder if I just rebar 2-3 times along the wall and fill those vertical cores if I'd structurally be good. Otherwise, I'm talking a lot of 80lb bags of mortar (15 blocks L x 6 blocks H of 8x8x16) lol
A few photos
Chicago Clay, it usually stays put and can be cut by the excavator, probably the best things you can say about it!
Pb
I've got that Virginia clay. A little softer but rocky. Not friendly to my drainage projects lol