Are these horizontal cracks in the foundation dangerous?

My family and I have just moved into a duplex that we’re renting. The house is joined to another house. We share one wall with the other house. We’re not in a row of townhouses.

I’m not a structural engineer, but have concerns about the foundation of the house. I’ve heard that horizontal cracks are bad in a foundation and we have some very long ones in the foundation that span the length of entire walls. One of these wall long cracks on one of the west walls extends right into the south wall and continues on. I’ve attempted to attach pictures of this particular crack to this post, but seem unable to.

The cracks have been patched/filled with concrete at some point, and it looks like the filled concrete has been sanded down to smooth it out, so it’s really hard to tell how wide the cracks actually are. The foundation walls don’t appear to be bowing, but I’d like to understand better whether or not the cracks are dangerous. There’s also vertical cracks in the foundation.

I know it’s hard to judge from just photographs, but are these cracks dangerous, considering that the walls are flat and flush? What’s the difference between a horizontal crack that’s dangerous and one that’s not? Or are all horizontal cracks something to be concerned about?

Thanks in advance to anyone who takes the time to reply.

How old is the house? All concrete will develop cracks the older the house, the more cracks,
How wide are the cracks? Hairline cracking is usually not a structural problem.
Horizontal cracking near or below grade may be caused by frost or the expansion of clay based soils when they get wet. Horizontal cracking often occurs shortly after the house is built, and may be the result of poor practice when backfilling. If the foundation walls are not being pushed out or over, there is probably not a structural problem
Are the cracks moving or getting wider? Stable older cracks are probably not a structural problem.
Are the house floors, walls, level doors, window frames are not pushed out of shape? (is the foundation doing what it is supposed to) Many foundations will settle somewhat, the older the structure the more settling can be expected, and be acceptable.
Without your pictures it is impossible to tell, but from what you say it does not sound like you have a structural problem particularly if the house is older. If it has been standing for 30 or more years it is probably not going to fall over real soon.
Cracks will leak water, which is another issue entirely, make sure your landscaping, gutters, etc… direct water away from the foundation. Efflorescence (white crystaline deposits) in or around the cracks indicate water is leaking through the cracks. Mr. Bubber will have plenty of advice for you should this be the case.

Mr Erik, good points and Q’s :wink:

SOME horizontal cracks might NOT get worse/widen (without ANYTHING being done)

SOME horizontal cracks will get worse over TIME.

SOME horizontal cracks can get worse/widen suddenly.

The fact that somebody apparently filled 'em with concrete on the inside doesn’t do squat.
HERE/photo, a horizontal crack and verticle crack were patched/concrete on the inside…
ZOOM IN and you’ll see the patching.

Same house, what needed to be done…(the outside of the wall)
Click each individual pic to ENLARGE

As Erik said, no pictures so its more difficult to say/help and its still best to be ON SITE.

This article, at least whats in this part-1 is pretty much right on…scroll down to PAGE 3

This article also helps explains some sht, about 1/2 way down, Basement Wall Damage

You/others see what ya see on the inside but that does NOT explain what can and does occur OUTSIDE…see deteriorated blocks and joints here…

Could post some news stories of homeowners who had a wall cave in, only had small crack(s) visible on the inside so, pictures wouldn’t hurt but even then we/NOBODY can tell ya what is going to happen to the wall(s),cracks in the future. Can only explain what we’ve seen for decades and what is BEST for them and, lol, its not any inside work/system/patching.

And please watch this short video…this is what i mean…and imo, NEVER EVER trust an inside system company…NOPE! Foundation problems in Pennsylvania, got milk?

Little Brown Bird, J Beck & E Clapton …Bubba got a bird for duh winter, and Bubba got a bird for the spring