Flipped Home – Cracks Appearing on Wall Corners – Cause for Concern or Normal

First I don't totally disagree with Tyler but his answer is a bit ridiculous. Only a concrete salesman would tell you to repour your foundation due to hairline cracks in drywall. Maybe the issue has something to do with the foundation shifting seasonally.

But all houses move a little throughout weather changes - humidity and temp. It is virtually impossible to ever create a house that will never have any cracks in the drywall unless you do everything perfectly and use only the best materials and keep the house climate controlled all the time. For 99% of the population adding on 20-40%+ more costs is not worth a few very minor cracks in their drywall.

So what can you do:

1. Take pictures and inspect the attic. You partly did this - not well because the pictures I see have insulation over the beams. If there is anything pulling apart you should be worried about the structure. If you start seeing trusses pulling (I have seen this) or gaps then you have a bigger problem - still not one that warrants a foundation repour. The fact is there might be a truss or beam that is not supported well or simply a cut that is 1/4" short on one side. A lot of times you can see cross beams in your ceiling drywall. This could be an issue with it moving or could just be old drywall or poorly installed drywall. We would need much much better pictures to piece this together.

2. Quit researching your dirt. Your house is already built, you live in it, why would you focus on something that you can't change? Your house has been up for 13 years and you have hairline drywall cracks. Did your builders do the job "right"? Who knows. Did they do a good enough job? Looks like it.

3. I am sure part of your problem is the temp/humidity variance between the different sides of your drywall. It is not a coincidence that the cracks came back as the nights neared freezing. Add more insulation, add better insulation, keep your home at a more consistent temp/humidity. It is also not a coincidence that this is happening on your second floor. Homes with real foundation issues have cracks everywhere including basement walls.

4. If I had to plop down money and bet why you keep getting these cracks I would bet it was simply due to the drywall installation. These are the cracks that you get when you don't float the outside of your ceilings. If everything is screwed in all the way through and wood is expanding and contracting at a greater rate than the drywall this will happen. I have answered how to float ceiling drywall before. I can tell you that this is your biggest problem - $50 drywall install. The company that came in basically redid the exact same thing as the original - did you expect different results. Did they think about cutting both pieces of drywall out and having one piece over that sensitive area? Did they think about using a different material? Nope just blame it on someone else and someone else that did something 13 years ago. I would laugh if contractors came back on a warranty and said that its your truss - so when they took your money they didn't need to investigate but when you take their time they do? I wouldn't believe anything they said period.

5. Second biggest issue is covering the drywall. When you have hairline cracks that pop up in the same places and you use drywall mud and sand/paint... well I can say that you should expect the same crack 98% of the time to show within 2 years. First get some mesh drywall tape. For a nasty crack I might use 2-3 pieces of tape layered slight different. Then you need to use plaster or spackle or at least something more flexible than your basic drywall mud.

Floor bounce is often a factor of the spacing and span of the joists. Assuming you are in the US, there was a time in the 70s when the building codes were still based on the pre-WWII lumber strength data. But after the baby-boom era in the 50s and 60s, most of the old growth trees were harvested and lumber was coming from new faster growing trees that were not as strong. Eventually the "Floor Joist Span Tables" that are used in the construction industry were updated to reflect this, but the lag time meant a lot of wood frame homes built in the 70s have more "bounce" than older ones or newer ones. It's not necessarily bad, it's just different than you might have experienced in a newer or older home. I have a home built in 1971, I noticed it the day I toured it before buying and I researched it, thinking that the home was defective. But the spans and spacings were correct, for the time it was built.

The vibration from the slab and the cracking may be due to the type of soil you have. Clay soils tend to change a lot each year as they absorb water in the winter and dry out in the summer. My house is on California Adobe soil, in the winter and spring I can feel vibrations coming from transformers in a utility substation 1/2 mile away, but by June or July, I can't feel them any more.