No, of course, I wouldn't agree with all those Protestant commentators if they disagreed with what the Church teaches. I just cited them to show that the idea of reading the appositive as referring to the word "Church."is a lot more widespread than just within Catholicism.
Googling around like that also illustrates another important point: that there is commonly a lot of disagreement amongst guys like this about doctrine, which is why I usually go first to a reliable, coherent, and internally consistent source of interpretation, i.e. the Catechism.
I'm out to an all-day Shape-Note Singing!~
That's why it's important to search the scripture for oneself. Teachers obviously CAN shed light and often do; however, if they contradict what's in the text...that's when a red flag goes up because political considerations or other considerations of the day can color church leaders' "interpretations". I wonder what was going on politically in the Catholic church when the Immaculate Conception was doctrinized in 1850 or thereabouts and when the Assumption of Mary was doctrinized in 1950.
As I look at that Timothy passage I become more convinced that the foundation is God...the "household" referred to in the earlier passage denotes believers; however, Paul is pointing out that the "foundation" under that household and the "pillar" which holds it up are God. Then Paul goes on to exalt in that foundation in the last verses of the chapter. Of course, as I said I would like to hear what a Greek scholar thinks about it as I don't know Greek. But the English and the Interlinear seem fairly straightforward to me.