Warning: these figures indicate the number of cases found in the data file. They cannot be interpreted as summary statistics of the population of interest.
This is not a question but an observation. You will usually be able to see for yourself what kind of material the exterior walls are made of. However, ask the respondent if you are not sure. Again, if there is more than one kind of wall material, record the main type of material (the material that covers the largest amount of wall space).