In this act the following terms shall have the meanings respectively assigned to them as follows:

Par. 1. - First Class Building. - A first class building shall consist of fireproof material throughout, with floors constructed of iron, steel or reinforced concrete beams, filled in between with terra cotta or other masonry arches or with concrete or reinforced concrete slabs; wood may be used only for under and upper floors, windows and door frames, sashes, doors, interior finish, hand rails for stairs, necessary sleepers bedded in the cement, and for isolated furrings bedded in mortar. There shall be no air space between the top of any floor arches and the floor boarding.

Par. 2. - Second Class Building. - All buildings not of the first class, the external and party walls of which are of brick, stone, iron, steel, concrete, reinforced concrete, concrete blocks, or other equally substantial and fireproof material.

Par. 3. - Third Class Building. - A wooden frame building.

Par. 4. - Composite Building. - A building partly of second class and partly of third class construction. Composite buildings may be built under the same restrictions as, and need comply only with the requirements for, third class buildings as to fire protection and exterior finish.

Par. 5. - Masonry. - Masonry shall include such parts of a structure as are constructed with stone, bricks of burnt clay, cement, or sand lime, hollow blocks of burnt clay or concrete, and stone or cinder concrete, both plain and reinforced work.

Par. 6. - Foundation. - That part of a wall below the level of the street curb, or, if a wall is not on the street, that part of the wall below the level of the highest ground next to the wall, or, in the discretion of the commissioner, that part of a party or partition wall below the cellar floor.

Par. 7. - Underpinning. - In third class buildings the wall reaching from the foundation proper to the under side of the sills.

Par. 8. - Height of a Building. - The vertical distance of the highest point of the roof above the mean grade of the curbs of all the streets upon which it abuts, and if it does not abut on a street, above the mean grade of the ground adjoining the building.

Par. 9. - Party Wall. - A wall that separates two or more buildings, and is used or adapted for the use of more than one building.

Par. 10. - Partition Wall. - ■ An interior wall of masonry in a building.

Par. 11. - Thickness of Wall. - The minimum thickness of such wall.

Par. 12. - Story of a Building. - That part of a building between the top of any floor beams and the top of the floor or roof beams next above.

Par. 13. - Basement. - That story of a building not more than forty per cent of which is below the grade of the street.

Par. 14. - Cellar. - That part of a building more than forty per cent of which is below the grade of the street, and in third class buildings that part of the building which is below the sills.

Par. 15. - Gas Fitting. - The work of putting together any fittings, pipes or fixtures or other appliances which are to contain gas for heat, light or power purposes and will be subject to inspection under existing laws.

[1918, c. 179, sect. 3, Special Act.]