Asked January 13, 2017, 10:45 PM EST
Fort Bend County Texas
Tough question. The answer centers around safety to your home, belongings, and humans. Twenty-Thirty feet may be the minimum. This is because of hanging branches. Pecan wood tends to be weak and large branches can fail without warning. This creates caution to roofing, cars, etc. Further, ground work on the job site can cause long term damage to the root system of established trees. So, the final note is to avoid trees that will have large branches that spread over driveways, structures, home, pool, etc.
You may want to hire professional advice and services. To find a certified arborist in your area visit http://ISA-arbor.com and click on "tree owner looking for certified arborist". Put in your zip code and it will pull up a list of arborists in your area.
Best of luck,