To exempt the interior finish of walls and ceilings in bathrooms from the requirements of Sentence 9.10.17.1.(1), which would otherwise limit surface flame-spread rating to 150, and permit a higher maximum flame-spread rating, on the basis that the incidence rate of fires in bathrooms is much lower than in most other parts of a residential suite, bathrooms are usually very small and generally have little effect on the rate of the spread of fire within a suite, and the higher rating will not contribute significantly to the spread of flame.