mr. cheng's solution is simpler and more elegant, but if you really wanted to use your sentence correctly, it would be: "It's Sally's and my house." Proper nouns before pronouns and that bit of modesty of putting oneself last. As you've already said, it's "our" house, so you just replace the collective with the individuals.
If your sentence was "We live in that house", then you would say "Sally and I live in that house" -- the "our" and "we" determines whether you use "I" or "me/my" in the sentence.