If you are a rent-paying tenant of your father-in-law, and if (as you seem to indicate) the rot posses a health hazard, your father-in-law, as your landlord, must remediate (repair or replace; clean up) the flooring. The law requires landlords to provide residences that are safe and fit to live in; this is called the "implied warranty of habitability." If he won't do so voluntarily, you could withhold rent to force him to do so (put the withheld rent in a bank account or other safe place; if/when he takes you to court for your nonpayment and you raise the lack of habitability as a defense, the court may ask you to deposit the money). Alternately, if you feel that this is an urgent health hazard, you could affirmatively go and bring a legel action seeking a court order requiring him to make repairs; you can get instructions on what to do/file from your court (e.g. the clerk).If you are a tenant and this is not a health or safety hazard, he has no obligationt to fix it; he can just carpet over it.If you are not a tenant, but a guest (allowed to stay there without paying rent) of your father-in-law, you can't force him to make repairs; guests, no matter how long they have been in a place, cannot require the property owner to change or fix anything.