In case that you conduct the interview somewhere outside of the house, then you should ask the informant about the main material of the floor of the household. In that case, if the interviewee mentions more than one type of material, you should investigate with him/her, which one is the main material or the material of largest proportion.
It is a general rule that when the walls, floor and roof of the household are made out of two or more materials, you should always consider the material with the largest proportion, and when the materials have equal proportions, consider the one with the highest quality.