Large Concrete Cracks in Basement 12

[cal91]

I was asked to look at some slab cracks in an unfinished basement. The house is coming up on a year old (when the warranty expires).

The builder was asked to come and look, and he said they were fine and they would not fix the cracks.

The cracks are near structural posts, and there is moderate elevation change across the crack. The side with the post is lower. I suspect there is not a thickened slab under the post and the post reaction has cracked through the slab. I have not seen any building plans however.

I am wondering if the IBC or some other source I could reference that defines acceptable crack widths and elevation differentials?

Any opinions would greatly be appreciated. Thanks!

 

[Rabbit12]

I can tell you this. If this was my house, this would be a major problem. Maybe not major in the long term performance of the house but it's pretty unsightly and you'd need a pretty good argument to convince me this is reasonable performance after 1 year.

 

[cal91]

I can tell you this. If this was my house, this would be a major problem. Maybe not major in the long term performance of the house but it's pretty unsightly and you'd need a pretty good argument to convince me this is reasonable performance after 1 year.

I'm with you but the problem is that the builder doesn't need to convince you that this is reasonable performance.

You need to convince the builder that it is not reasonable performance, and that they are legally obligated to fix it. Good ole' burden of proof.

 

[TheDW]

You could maybe argue floor flatness and levelness? It might get them to grind it down and make it look better at least.

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[Ron247]

I keep saying I am going to write a book on "Contractor, Engineer and Architect Excuses". My favorite one for a Contractor's excuse for new concrete that has big cracks is "We all know concrete cracks. I would be more afraid of concrete that did not crack than concrete that cracked like this."

Those cracks well exceed normal shrinkage.

 

[JoshPlumSE]

Have the homeowner send the builder a letter which states that they've consulted an independent engineer who believes this damage represents a significant structural defect and that if they don't propose a remedy then they will be forced to pursue a legal remedy.

You don't need to convince the builder of shit. You need merely point out that this is (in your opinion) a breach of contract / warranty and if they refuse to acknowledge that then they'll have a lawsuit on their hands.

 

[STrctPono]

I understand that it's a cut throat market for Engineers in residential design and any squawking could lose you your next job but it's a darn shame that residential builders aren't held to higher standards and that this is "par for the course".

 

[EdStainless]

If you go up a floor or two are there any signs of this post settling, like cracks?

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, consulting work welcomed

 

[dik]

50 years back, being a 'wise old engineer' then... I was sure that concrete will shrink... so much so that I told the contractor not to remove the plywood between concrete pours... the concrete would shrink and you could then pull the plywood out... if it's still standing, I bet the plywood is still there...

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[gte447f]

Agree with Ron that this most likely started as shrinkage cracks (probably right after concrete was poured). As the shrinkage cracks grew, shear strength of slab was reduced at the crack locations due to loss of aggregate interlock. Eventually you ended up with a concentrated point load eccentrically located at the very corner of an isolated section of slab on grade. Naturally this condition resulted in settlement of the corner of the isolated section of slab locally at the corner under the concentrated point load.

Not sure what the 4-2x6 stud pack is there for, but the real load seems likely to be from the 3-2x4 stud pack (2 jack studs and a king stud) at the corner that is supporting the end of the header beam that can be seen in the photos above. The 2x4 wall is obviously load bearing as can be seen from the photos of the floor joists above. Around here (southeast US) that slab would most likely be nominal 4" thick with an 8"-12" deep by 12"-24" wide monolithically poured, thickened slab under that load bearing wall. Reinforcing in the slab would probably be 6x6 W1.4xW1.4 welded wire reinforcing that was not chaired properly and was stomped into the dirt at the bottom of the slab during placement of concrete. The thickened slab under the load bearing wall might or might not have 2-#4 longitudinal bottom bars specified.

Looking at the photos, I doubt if there is a thickened slab under the load bearing wall because I don't think the shrinkage cracks would propagate through the thickened area, but I would not bet on this. I would be curious to investigate the presence/location of a thickened slab by drilling through the slab.

Based on the photos, I would consider this a relatively significant structural deficiency, albeit related primarily to serviceability. If left unaddressed, that condition will definitely affect the marketability and value of the home if/when the owner attempts to sell it. I routinely assess much less significant "structural" concerns related to residential real estate transactions.

 

[Tomfh]

favorite one for a Contractor's excuse for new concrete that has big cracks is "We all know concrete cracks. “

And no engineer has ever used that excuse, have they.

 

[XR250]

This is the standard lingo I hear from contractors...
"There are two kinds of concrete: 1) Concrete that is cracked. 2) Concrete that is gonna crack"