About 90 is the top unless you have CO2 enrichment when you can go to about 100. Remember, though, that spider mites and other nasties love hot arid places and reproduce faster with higher temps. I keep my garden around 75-78 with rh 45-55%, and I've had no problems (yet) with pests or mold and the plants are healthy and happy. If you must grow in an attic, invest in an exhaust fan that will evacuate the area in under 5 min to help keep heat under control. Adding a charcoal filter to the exhaust system (before the fan) makes it serve double duty by keeping the skunk at bay.
Good luck!