During the 1960’s and 1970’s, several catastrophic fires in residential dwellings prompted changes in building codes. Preventative measures, aimed at stopping and/or slowing the spread of fire through a house were introduced and enforced. One such requirement is fire blocking, defined by the International Residential Code (IRC) as the following:
Building materials installed to resist the free passage of flame to other areas of the building through
concealed spaces. The IRC stipulates that blocking (accomplished by nailing a piece of2X4 lumber between each stud in the framed wall) must be installed as follows:
1. In concealed spaces of stud walls and partitions.
2. Vertically at the ceiling and floor levels.
3. Horizontally at intervals not exceeding 10 feet.
4. At openings around vents, pipes, ducts, cables and wires at ceiling andfloor level, with an approved material to resist the free passage of flame and products of combustion.
Although these blocks will not stop a fire completely, they will help contain flames for several hours. If you think about it, a wall stud bay without blocking, can serve as a vented chimney for flames and combustible gases. This is particularly worrisome in older houses where balloon framing was used. Within minutes, a fire started in abasement kitchen can travel several stories through a stud bay and set the attic ablaze.
Therefore, we installed blocking (at approximately 5 feet) between each stud in every interior wall on both the first and second floors, and sprayedall holes around plumbing pipes, HVAC lines, and electrical wires with special fire-resistant foam.
The IRC goes on to stipulate that, Dwelling units in two-family dwellings shall be separated from each other by wall and/or floor assemblies having not less than a 1-hour fire-resistance rating when tested in accordance with ASTME 119.We accomplished this by installing strips of 5/8-inch “fire-code”drywall above the top plate of each interior wall on the first floor(done prior to building and standing up the framing walls.) The same5/8-inch drywall will be used on the ceiling on each floor since it carries a minimum 1-hour fire rating, as opposed to the 30-minute rating attached to ½-inch drywall. In addition to being thicker, fire-code drywall has a denser core and is manufactured with glass fibers that eliminate crumbling in heat.
Lastly, we had to address the 30 recessed lights on the first floor. Since each of these lights is cut into the fire-code ceiling drywall, we were required to install a box (carrying a 1-hour minimum fire rating)around the top of each light fixture. We had the option of purchasing pre-made ready to install boxes, or building them ourselves out of framing lumber and 5/8-inch drywall. In view of the significant price difference – $130 per pre-made box as opposed to $10 per home-made box– we opted to build them ourselves. Considering that there were 30lights this saved the client approximately $3,600.
