What Documents Do I Need for My Extension on a Marriage Visa in Nong Khai?

You may also require a certificate to confirm you are still married. Samut Prakan ask for it and it’s on their list of docs to be presented. They also request photos in house of all rooms excluding bathrooms

Roughly, you'll need, copies of the relevant pages in your passport, your marriage certificates (maybe your affirmation of freedom to marry document from your consulate), a bank letter, updated bank book showing the 400K baht has been in your account for 2 months before you apply, your thai wife's documentation, (i/d, house book), photos of you and your wife in front of the address where you live, sitting in the living room, a hand drawn map to your place AND those are just the things I can remember that are required at most immigration offices.

That's why I say GO to the immigration office before you need to get your extension and have them give you the hand out listing the documentation you need.

You need to go to the thai immigration office in Nong Khai BEFORE you want to apply for your extension and get the hand out that lists your documentation requirements