Contractor Rob Paisley details fire-rated wall assemblies for a new four-story building that's shoulder to shoulder with its neighbor.
Already three stories tall as seen here, this Portland, Maine multifamily building will rise another story, plus a rooftop patio. It must be isolated from the existing building at right by a two-hour fire-rated assembly.
Contractor Rob Paisley shows the two-hour "burn wall" he's installing level by level as he frames each floor of the new building.
Two one-inch layers of gypsum board are rated to provide two hours of fire protection for buildings on either side, if the other side should catch fire. The H-stud holds the gypsum board in place.
Aluminum clips hold the steel H-stud firewall framework off the wood framing, with a typical 3/4-inch gap. In a fire, the clip would melt and allow the burned framing to fall away without pulling down the wall, which would remain secured to the other building and isolate it from the fire.
A view down the firewall. The old building is on the left, the partially framed new building is on the right.
The yellow GP DensGlass gypsum board at right is protecting the walls of the two stairwells for the building, which also must be fire-rated assemblies. DensGlass was chosen for this assembly because of its weather resistance as well as its fire resistance, since the assembly must be left exposed to the weather for weeks during construction.
A view from underneath a stair landing within a stairwell shows the ledger for the floor frame. Structural framing is not allowed to penetrate the fire-rated gypsum board on the shaft walls, so structural screws are used to support the ledger.
The ceiling of a hallway between the elevator shaft and the garage on the building's street level. Both walls are fire-protected. Like other floors in the building, the framing above is fastened through the DensGlass with structural screws. This ceiling will also receive one inch of gypsum board.
A view of the underside of a stairwell from the garage level. Gypsum board continues through the floor assembly to completely isolate the stairwell from the rest of the building. The DensGlass gypsum board extends down an inch to meet up with more DensGlass that will be applied to the ceiling. Each floor of the building will be isolated in this manner from the floors above and below.
This metal fire door separating two protected spaces had to be detailed and attached so that the frame for the door could fall away from either side, leaving the door itself in place to protect the other side of the wall.
"There is no plate-to-plate wood connection anywhere in this building" between the fire-protected spaces, explains Rob Paisley. The truss hangers shown here provide a one-inch space that allows gypsum board to be slipped between the floor frame and the wall frame.
Another look at the specialized truss hangers, which allow wood floor framing to be isolated from wall framing by fire-resistant gypsum board.
As the new building rises up above the roof of the adjacent building, the two-hour firewall rises up also. Here, Paisley works on the wall frame. The protective gypsum material must rise three feet above the top of the adjacent building's roof access structure at this location.
A view along the roof of the older adjacent building toward its roof access structure and deck. This wall will receive a three-foot fire-resistant barrier rated for two hours.
The fire-protected stairwell for the new building rises up above the roof of its older neighbor. This section of wall will receive a two-hour "burn wall" at this location, extending three feet above the neighboring structure.
A view of the new firewall assembly over the rooftop of the neighboring building's roof access structure. The gypsum board is intended to protect either building from a fire in the neighboring structure.
A view of the partially completed firewall as seen over the top of the neighboring building's rooftop access structure. The frewall is being assembled in stages as the new building goes up and provides the workers with a working platform.
Contractor Rob Paisley fastens an aluminum breakaway clip to the wood wall frame of the new building. If the wall should catch fire, this clip would melt and allow the wall to fall away, leaving the protective gypsum board assembly intact and still fastened to the neighboring structure.
Paisley attaches the firewall frame to the wood wall of the new building with an aluminum clip.
On a snowy day in spring, the crew constructs the gypsum-board and steel firewall assembly, working on the roof of the existing building next door. Later they will cover the firewall with framing and siding from this side and integrate it into the roof of the existing building.
The crew slips gypsum board into the space between the old building and the new frame under construction.
The crew slips an H-stud over the edge of the double layer of 1-inch gypsum board.