What does it mean to demurrer in unlawful detainer?

A demurrer means you claim the allegations made in the complaint do not support the cause(s) of action sued upon, or they are legally barred. You have to file with the court and serve on the plaintiff your written demurrer, but you need to look at the code section on unlawful detainers as it limits what you can demur to. Is it the owner of the house who is suing or the owner's estate if he has died non-owner can not sue. Is there any thing incorrect as to the three or thirty day notice given, such as the amount of rent claimed owed. Is the property covered by rent control. Did you have an agreement, oral or written, that the work you did would cover the entire amount of rent owed and/or would reduce the future sales price for you [breach of contract]. If the agreement was only that you did not have to pay any rent, then you have nothing "invested" in the house because your work was just paying the rent. If you are entitled to more, you may want to file a cross-complaint to get the additional sum back. You need to speak to a local tenant's attorney to see what can be done; they normally do not charge for the first 20 minutes of the initial visit with them.