If your builder wouldn't allow it, you picked the WRONG builder.....period!!!!!!!!! An engineer should look at it. If the engineer fails it, you might have to take the builder to court .

Are there relief cuts? There realistically is two types of concrete, cracked and yet to crack and the purpose of relief cuts are so the chance of these cracks are reduced. Is this a full basement and this is the cellar floor? House built on a slab? Tract or developer home? Custom home?

If an engineer "failed" a cracked concrete slab, I'd fail him, because he knows little about construction. millworkman is correct. Concrete cracks. Wood grows on trees.

@robin0919 @millworkman @Joseph Corlett, LLC Thank you all for your comments! The home is a "luxury" (according to the builder) tract home. It is costing a lot of money (it's CA) so I do not want to end up with a home that has any major issues. The builder has done a lot of things wrong (mostly cosmetic/my option choices to my knowledge so far) so I do not have a lot of confidence that things were done correctly. However, there is a hole in bedroom one wall and it looks like they did not tape the drywall seams. Luckily a friend saw this and pointed it out although I am not sure what to do about it unless I just walk away from the home due to the issues. (A photo is attached if have any advice on that).

There is no basement. I am not sure about relief cuts, I would need to ask. However, the crack is not necessarily in an entirely straight line across the width of the home. At a certain point it starts to run on a bit of a diagonal. If it was a relief cut would it be a straight line? The foundation was poured approximately last September (2019). The home was framed in approx. Dec 2019. I know concrete cracks, but should it have this large of cracks this soon? I just want to make sure that I won't have any moisture issues, and that it won't cause any other structural problems.

Concrete can and will crack at any time basically from day 2 on. Typically not an issue. Relief cuts would be straight lines and quite obvious as they would pretty much cut up the slab into square or rectangular quadrants. A tract home builder ("luxury" or otherwise) will not allow an inspector as technically you do not on the house until closing. The hole in the drywall is an hour or two work to repair and not a big deal. The crack in the slab would not bother me either. The walk away decision is up to you but expect to lose your deposit and any money up put up for upgrades.

@millworkman, Thank you again. I am not concerned about the hole in the drywall, but that fact that the seam of the drywall does not appear to be taped. I have been told that all seams should be taped. Did you notice that? I am a novice and I am just trying to protect my investment the best I can. I appreciate your help.

Seam looks way to flat to me to not have been taped.

It does look like it was taped. It's likely a careless worked did something that resulted in the hole and the paper pulled away from that section.

If you have a "luxury" tract home, you now have "luxury" cracks.

The Canadian new home warranty max acceptable concrete slab crack is 4mm.

https://www.tarion.com/cpg/foundation-basement/foundation-basement/concrete-basement-floor-cracked

Now I wonder if the slab crack is related to why the hole in wall. Is that separation I see in hole possibly wall cracking. Where is wall issue in relation to wall crack/hole physically?

Here's what the government mandated warranty programme in my jurisdiction (Ontario) says about poured concrete foundation wall cracks:

Less than 6mm is minor. If it widens, it should be repaired to prevent eventual water leakage.

Same according to the B.C. Residential Performance Construction Performance Guide., p.25.

@Flo Mangan, I think the hole in the wall is from someone punching through. There is a light switch on the opposite side of the wall that I think is in approximately the same location. Next to the light switch they poked a bunch of holes in a line as if looking for a stud. There is another place below the hole that is not as bad, but it too seems like someone punched through -- the wall is raised in a circular pattern and there is a small hole. Maybe they messed up when installing the light switch? The crack in the slab goes through the same room but is probably 6-10 feet away from the wall.

Ask builder for a meeting if you haven’t already and ask for his/her slab/foundation expert to come and observe and give inspection and assessment. Then send email with photos to everyone in the on site meeting documenting very factually (non-emotional) the points and actions agreed upon. This could be valuable 10 months after moving in in case you have further indications such as tile cracking. As a minimum, I would request repair of cracks to help keep things as stable as possible. Good luck.

That crack looks fairly big. I’ve poured a lot of slabs and concrete walls and have never seen a shrinkage crack that wide. It looks like 3/16”? The ones that I saw are less than 1/16, more like hairline cracks. I’d get that checked out by a structural engineer.

You may also want to get yourself a 2 foot and a 6 foot level and make sure that slab isn't falling off on one side of that crack. To me, this crack - opened up like that - seems indicative of not enough support under it. If it keeps the plane, I'd be less concerned - but if the level rocks at the crack, a deeper discussion is warranted.

Good point just_janni. I too am concerned about slab support system.