According to the manufacturer, there is no minimum. Apparently the solvents and design of BORACARE enables it to be absorbed by treated wood right down to freezing temps. With that being said, I would have to add that the warmer the temps the easier it is to use and the faster you'll get absorption by the surfaces being sprayed. At least that's been my personal experience. I have used it down to 50 degrees and have not noted anything different but never tried any colder so I don't know about 35 degrees. Since you are treating inside, the exposed wood should be protected which to me means you should be able to get the same results. If you have further questions, give us a call on our toll free at 1-800-877-7290.