You are a little confused. A marriage does not need to take place at a chapel/religious venue to be sacramental (at least in the Roman rite) the ministers of marriage are the couple who confer the sacrament on each other. This means that the only requirement for a marriage to be sacramental is for both parties to be baptized (hence why a court house marriage may be sacramental). The marriage automatically becomes sacramental on the baptism of both parties.
However Catholics are bound by canon law which requires them to be married in a Church or obtain a dispensation to marry outside of it. I don’t know why this impacts validity rather than licity but that is the case. I suppose the nearest example is saying that a state has the right to set it’s own requirements for a couple to civilly marry in it.
The conditions for marriage are:
Openness to life
Faithfulness of the spouses
If one of these is not met at the time of the exchange of vows the marriage is not valid and if it could be proven to a tribunal the marriage would be annulled. This means that there never was a marriage.
Assuming one of the parties are not baptized then the marriage is natural and may be dissolved.
This is granted by the Petrine and Pauline privileges.
The Pauline privilege is based on 1 Cor 7
12 To the rest I say, not the Lord, that if any brother has a wife who is an unbeliever, and she consents to live with him, he should not divorce her. 13 If any woman has a husband who is an unbeliever, and he consents to live with her, she should not divorce him. 14 For the unbelieving husband is consecrated through his wife, and the unbelieving wife is consecrated through her husband. Otherwise, your children would be unclean, but as it is they are holy. 15 But if the unbelieving partner desires to separate, let it be so; in such a case the brother or sister is not bound. For God has called us[b] to peace. 16 Wife, how do you know whether you will save your husband? Husband, how do you know whether you will save your wife?
The Petrine privilege is an extension and I assume based on the fact that God does not join the couple in a non sacramental marriage.