The easy answer is we can use an existing survey when the lender and title company say it's ok -- the current survey is valid and permissable to use per each of their underwriting guidelines. He who has the gold makes the rules!
Another easy answer is we can use an existing survey when no changes have been made to the property since the survey was drawn; However, there are times when changes have been made to the property since the survey was drawn and it's still ok to use an existing survey! It just depends what the changes are and if the lender and title company really care about those changes -- there are many changes they do not mind. One example in one transaction is (and it changes depending on the title insurance and lender underwriting guidelines) the survey had a 12x12 permanent patio drawn. The homeowner added more patio using flagstone. The seller very honestly and accurately disclosed on the T-47 Addidavit that the property had one change: There is additional patio approximately 12x8 using flagstone and landscape grass to the east of the existing concrete patio, and the lender and title company both said, "No problem!" The very general rule of thumb is rocks and grass can be moved (typically not drawn) whereas concrete slabs permanently fixed typically are drawn very generally speaking. But an existing survey always has to be approved by the lender and title company, per their specific guidelines.
A person who pays cash for a home may not care to have a survey, so in that case, it's moot. But if a buyer is financing, a survey will be required and who pays for that survey -- the buyer or the seller -- can be negotiated and is part of the legally binding TREC contract or if the seller has one on file, it's worth it to present it and see if the existing survey may be used or if a new one must be drawn.
And another easy answer is: As long as the seller signs a T-47 Affidavit (a form promulgated by the Texas Department of Insurance) filling out six statements of fact before a notary, one including no changes have been made to the property since the survey was done, or, here are the changes and the title company and lender see the statement of fact and say it's ok, then we can still use the existing survey alongside that T-47 Affidavit.
What is a survey, anyway? A land survey for purposes of selling a home in Texas is a diagram that shows legal boundaries, easements, encroachments and right of ways. It will often have the perimeter of the house, the fenceline and anything permanently placed within the property line, like a storage shed on a slab foundation or outdoor covered patio area on a slab foundation or an inground gunite pool drawn in. All of the boundaries are drawn on a survey. If it's a plastic kiddie pool, a clothesline or a temporary fence for maybe a temporary puppy dog run... Not really applicable here.
Sample Survey in Keller Texas Sample TREC Contract with Survey Paragraph on Page 2 of 9