Street in New York City, built in 1934, was the city's first house to use glass blocks as walls. Skylights and sidewalk lights Glass blocks used in flooring are normally manufactured as a single solid piece, or as a hollow glass block with thicker side walls than the standard wall blocks. These blocks are normally cast into a reinforced concrete gridwork or set into a metal frame, allowing multiple units to be combined to span over openings in basements and roofs to create skylights. Glass wall blocks should not be used in flooring applications because the way in which they are manufactured does not allow them to support a load. Construction methods Glass wall blocks are fixed together to form complete walls by several methods – the most common method of construction is to bed the blocks together in a Portland cement-based mortar with reinforcing rods of steel placed within the mortar as recommended by the project architect or block manufacturer. Other methods of construction include several proprietary systems whereby the mortar is replaced by timber or PVC extrusions. Specialty types Specialist glass blocks are produced for various applications including: Bullet and vandal resistance Bullet and vandal resistant blocks are generally solid glass or have very thick side walls similar to pavement blocks. Fire resistant Fire resistance of varying degrees can be achieved by several methods. Standard production hollow wall block will offer little fire resistance; however, resistance is improved by utilizing specially produced hollow blocks with thicker sidewalls, or the inclusion of a special layer of fire-resisting material between the two halves of the block during manufacture. Some manufacturers of glass blocks have developed a method of bonding two glass blocks together with adhesive, producing blocks of up to 160 mm (6½") thick with enhanced fire resistance. It is important that the block manufacturer's recommendations are followed with regards to the installation of fire resisting glass block walls, as without special construction techniques, the wall will not achieve the desired fire resistance. Gas insulated A recent innovation in the manufacture of glass blocks is the inclusion of argon gas within the hollow center of glass wall blocks. This advancement in production technique has resulted in a glass block which is able to offer significantly improved thermal insulation properties. Colored Some hollow glass wall blocks are available in colored variants. These colored variants fall into two categories. The first type