I am building my first home with a builder and during the framing stages we had a lot of rain for weeks. Drywall and insulation is not yet done. As seen in the picture there was water collection and I'm not sure if the sub floor has developed a sag? The water from the first floor has leaked into the basement. Should I be worried about Mold?
Do I need to ask my builder to replace this floorboard?
Also what kind of floorboard is this? Thanks in advance
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Oriented Strand Board (OSB)

Start with a simple conversation with the builder and air your concerns and see what he says. Does no good to replace anything if the leak is not found and fixed. Good you have pictures.

Thank you very much hkstroud and talaniman. This was during the framing stages and the roof was not up. Since it was raining for weeks the builder couldn't roof the house. Do you know how much these OSBs can withstand water collection ? Again appreciate your responses and thanks a lot.

Some type of tarp or cover for the roof should have been used to prevent this type of damage, but since it wasn't the full extent of the damage has to be assessed even if that means tearing up the floor. What has your builder suggested? Don't sign off until YOU are satisfied and all your questions are answered to your satisfaction.

I have not looked up the specs and guarantees of the products in question, but the onus is on you and the builder to verify if they have lived up to those specs and guarantees, and take the appropriate actions. I will say this though, who leaves an unfinished roof exposed to weeks of rain in the first place?

I doubt any warranty, or guarantee covers such actions.

OSB is compressed wood chips and wood fiber glued together with a water resistant glue. It will shed, but is not impervious to water. It is not unusual for it to rain during the building process. OSB will delaminate around the edges if continuously exposed to water for a period of time. The flat surfaces will shed water quite well but water can be adsorbed in through the edges. Builder would have done well to have swept out the water after each rain.

Don't panic. Inspect yourself, looking for swollen edges. Discuss with builder and express your concerns. Wood swells and contracts with moisture. If edges are delaminating I would have some concerns. Not about structural integrity but about squeaking floors. If you are not confidant in your own knowledge and judgment consider hiring an independent individual (a carpenter) for an opinion. A quick walk through by an experienced carpenter can tell you if there is anything to be concerned about.

I think you will find the flooring is most likely Advantech, 3/4" T&G. It can tolerate the water, at least for a while. I too wondered why the roof wasn't on with windows installed. I hope the roof is on now.