We recently moved to the US Northeast and bought a 6 year old, two level plus basement house. I've been finishing the basement and have noticed several floor joists are splitting. I come from a country where this would not look good, but where there are also very few basements and no really cold, dry winters.
I'm inclined to write off some of the joist splits due to the climate, but a few are significantly split, offset, and/or split almost the length of the joist (see images). The image with the big offset shows one that has noticeably worsened during the winter months, and I'm reasonably sure the bangs we've heard have been the joists (not just normal thermal expansion/contraction).
My questions are: When do these become a problem that needs attention? Is this normal for the area, or did the builder cheap out on his timber? If this is not normal and a problem, what approach would you take to fixing it; would you start by calling the builder and giving him an opportunity to get it right? (after 6 years...) Would appreciate any help you can offer. Never had to deal with this type of issue. Thanks.