Before marriage, one party invests in the renovation of the other party's house. How to divide the property?

First of all, the commercial house belongs to Mr. Tang's personal property, and the decoration invested by Ms. Zhang belongs to the appendage of the property. According to the Property Law, when real estate is attached to chattel, the ownership nature of real estate will not change. The value of movable property materialized on real estate still belongs to the owner of real estate. Therefore, the real estate in this case does not belong to the same property, so it does not involve property division. Secondly, the reason why Ms. Zhang invested in the renovation of the house is mainly based on her expectation and judgment of marrying Mr. Tang, which is an attachment to the lover's property under this condition, rather than a gift to Mr. Tang. From the social common sense, even if the decoration money can be identified as a gift, it should be conditional on the marriage of both parties. It is wrong for Mr. Tang to refuse to return the woman's decoration money as a gift. Thirdly, the love relationship between Tang and Zhang, as a folk custom, belongs to the constraint of moral norms and is not the scope of legal adjustment. However, at the termination of the love relationship, because Ms. Zhang paid Mr. Tang's decoration money, Tang, as the beneficiary, had no legal basis for obtaining benefits, and Ms. Zhang caused losses. There was a causal relationship between them, so Tang's behavior constituted unjust enrichment. The relationship between them constitutes the debt of unjust enrichment in civil law, which should be adjusted by the General Principles of Civil Law. That is, Ms. Zhang enjoys the creditor's rights and Mr. Tang bears the debts. Therefore, Ms. Zhang has the right to ask Mr. Tang to return the decoration money she paid.