You were smart to walk away and with your money. We were like you when we had our last house built. Young and inexperienced. We trusted our builder which was a huge mistake. We saw a crack on the side of the slab but excepted the explanation the builder gave us. Eventually we had structural damage in the same area where the crack was formed. Every pipe under the master bathroom was broken and separated. When you have cracks (hairline or larger) in a new build it is time to get an independent inspector involved. Losing money is hard but dealing with major issues years later is worse. Remember, the builder usually walks away after a year. Even trying to sue is not always the solution since some builders close the business and reopen later under another name. We were lucky since the builder provided a warranty plan that covered structural issues but we had to fight everyone tooth and nail to get things covered. Consider this a life lesson for you. We did. You never look at builders the same way and you spend the extra money to have someone inspect all areas during the building process. I am glad you were able to get out of this nightmare. However, I feel bad for the person who will be buying this house.

Please update on how the problem was handled! I have me own tale of woe and hopefully can be an example of what can happen if you move into a house that has a mold problem. My husband, my son and I moved into our brand new home in Jan 2016. Literally a month later I began having issues with what I thought could be liver (nausea, pain in my right side, my right side under rib cage felt as if it were swollen) and I went to doctors, of course there was nothing wrong with me, but then my skin went bonkers, became red, so irritated that smiling hurt! And I won't even bring up all the countless respiratory problems! I've lost appetite, lost weight, but then suddenly gained it all back plus some more. My skin problems became a daily struggle... I could go on and on! To make a long story short, we're moving out in December! I can't wait! There's black colored mold seeping through cracks in shower stall of our master bathroom and I haven't been sleeping in my bedroom because of the smell. We're foreclosing. F this noise!! We wanted this house so much and were so excited to own a brand new home not knowing how miserable it can make us! (I have allergies and was hoping a brand new house would mean clean environment for me) OP, protect your kiddos, stop this train before it derails! And I know how you feel about your son's kindergarten, it's such special time for him and you and now it's all uncertain and it causes anxiety because you want to provide stability for your child. My little boy started kindergarten too in August and we're going to transfer him to a different school once we move. I can't wait til we're out of this house! Please get an attorney involved to help you get through this nightmare without losing the battle. And please update on the progress and I wish you happy ending!!!

Based on what you've said, this certainly seems like the builders fault. Getting them to eat the cost may be difficult depending on how your contract is structured. Personally I'd be much more concerned about the mold. My understanding is that you can kill surface mold but not mold that has penetrated the surface. E.G., any chemical that can kill mold has particles too large to penetrate wood or other materials to get to the roots. If it's in a place that will no way ever get wet or damp again then you may be OK as it should remain effectively dormant. If it ever does get wet or damp then the roots that weren't killed will begin to grow and you could have some serious problems depending on the type of mold. Also look in to what chemicals were used and what impacts they may have on your health.

@joseph_corlett People have mold panic. Folks are right to be concerned with anything in their homes that may affect occupant health and safety. To be sure, lumber yard mold is common on framing materials and is inactivated after the home is dried in. Most folks will understand that if the builder will take time to explain and a simple internet search can confirm that no treatment is typically required. Pull-down stairs, however, are not typically stored outdoors like framing lumber is, and not installed until after drywall-- so they never get wet. Indeed, by the time interior trim, interior doors and pull-down stairs are being installed, the interior environment of the home should be conditioned using either portable equipment or the home's HVAC system. If drying in a home were the only condition required to prevent mold, it would not have taken up residence on the OP's pull-down stairs. While we don't have all of the information, it's not that difficult for anyone with knowledge of basic physics or building science to connect the dots. The photos, combined with the OP's description that spray foam was installed under the roof deck, that there is mold on the rafters, and that the HVAC system is not operational points to a moisture problem in the (unvented) attic. I suspect your physics is fuzzy, so let's take a look at what's going on. Hot air rises. Moist air rises (it's less dense than dry air.) In a home, that means moisture and heat can accumulate in the attic volume. Designers can address those conditions by choosing to either vent the attic or to create a "conditioned" attic. The building code doesn't dictate the choice, but it does provide specific requirements to be met in each case. The designer of the OP's home has opted for a "conditioned" attic. I'm not sure which code is in effect in Texas at the moment, but in the 2018 IRC, the requirements for unvented attics are listed in section R806.5 Among other things, the code requires the installation of a vapor diffusion port at the highest point in the attic and that conditioned air be supplied at a rate greater than or equal to 50 cfm/1,000 sq. ft. of attic area. We don't know if the first condition has been met, but we know that the second hasn't. Without the supply of conditioned air, the relative humidity in the attic is obviously sufficient to allow mold growth. Spray foam insulation is wonderful stuff, but it is unforgiving of installation errors. In this case, some form of temporary attic ventilation should have been provided and the installation of spray foam in the attic should have been deferred until the HVAC system was operational. Getting the HVAC system operational should halt the propagation of mold and an expert can be consulted with regard to any abatement. At today's prices for spray foam insulation, a conditioned attic is a significant investment. Homeowners will be well served to ensure their builder knows how to construct one without causing problems like the OP's.