Yes, they can require repairs prior to refinancing. Rotting deck means your deck and wood trim have either wood rot or some other "wood destroying organism". This could be as simple as wood rot, dry rot or as complex as termites. The appraiser is trained to look for those items and the bank won't finance a property with rotton wood/dry rot or termites. Once it is repaired, then the appraiser would need to come back out to check to make sure the repairs were done properly. BTW, if there are termites, the lender will require that you treat for termites too and prove it with a clear WDO report.
If you go back and read your current mortgage you will see language that says it is up to you to maintain the property. So even your current lender can send someone out to check the condition of your property. That's really rare just to have an appraiser show up without a refi or a sale but it's perfectly normal in a refi or sale of the property.
