For you rookies the process can be a breeze but for a newbie there can be many snags along the way. Sometimes two people can go into the office and come out with different info. My friend has an "O" visa but needs to go to Laos every 90 days to renew it. The only around this is to go back to UK and request a 1 year visa.
Here is some of the information for visa extension in case of foreign husband with Thai national wife, as of the 3rd Dec. 2008. Pamphlet available at IO
Be advised to bring original and two copies of each document below, though if it's a letter to the IO the original document plus one copy.
1 T.M. 7
2 Photo copies of passport or travel document (Complete with copy of all pages that have anything to do with the current visa, re-entry visas, arrival stamps and current TM 6 slip etc.)
3 Valid visa, category Non-immigrant "O" or"B" (This Visa can only be obtained from a Thai Embassy or consulate outside the Kingdom of Thailand)
4 In case of working, the average income of the husband must be not less than 40,000 Thai Baht. If the husband works he must have a Work Permit, Income Tax papers from previous year (พงด 1, 91, 94) or have ฿4000,000 up to husband .
5 Or in the case receiving pension.
Applicant must provide evidence of a monthly pension with a minimum of ฿40,000. Evidence must include a letter of certification issued by the Embassy/Consulate of which applicant holds citizenship (E/C stamp needs to be verified by Thai MOFA Consular Department Chang Wattana Road BKK) and husband must show money exist in Thai bank ฿4000,000 before 2 months (Evidence and letters etc. accepted in English and/ or Thai only, all other languages must be translated and verified)
6 The bank must issue a letter of verification (Bank Statement) Stating the current balance of the savings deposit account (Bank Statement should be made the same as application of visa extension is submitted) Copies of all
pages of savings deposit account pass book ( Note: money must be in Thai bank before 2 months)
7 Marriage Certificate
8Wife ID Card and House Registration
9 2 photos 4 x 6 cm Full face within past 6 months
10 Birth certificate of children (if applicable)
Application fee ฿1,900
12 house map
13 House photo, photo of spouse in bedroom, photo in living room (Wrong
They want photos of both
of you in the living room in the bedroom and outside
14 And any other document the IO wants