The latest from an ambitious multi-family infill project in Portland, Maine
3 MIN READ
Framers attach a ledger for a stair landing to the stairwell shaft wall, after first fastening a strip of GP Gold Bond gypsum board in place at the ledger location. Framing multiple fire-protected elevator and stairwell shafts is tricky when no wood-to-wood contact between the shafts is allowed, observed contractor Rob Paisley. This staircase will help keep the shaft plumb and stable as the walls rise.
Portland, Maine, is like many cities on the Atlantic Coast: In the popular parts of town, housing is scarce and property values, along with rents, are rising. In the older, fully built-out parts of the city, developers are looking for high-density solutions. In many cases, the answer is an infill project. Outdated, older single-family homes are being torn down, and the few small remaining empty lots are being developed to support shoulder-to-shoulder multifamily construction.
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Already three stories tall as seen here, this Portland, Maine mu…
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.
Ted Cushman/JLC
Contractor Rob Paisley shows the two-hour "burn wall" he's insta…
Contractor Rob Paisley shows the two-hour "burn wall" he's installing level by level as he frames each floor of the new building.
Ted Cushman/JLC
Two one-inch layers of gypsum board are rated to provide two hou…
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.
Ted Cushman/JLC
Aluminum clips hold the steel H-stud firewall framework off the …
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.
Ted Cushman/JLC
A view down the firewall. The old building is on the left, the p…
A view down the firewall. The old building is on the left, the partially framed new building is on the right.
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The yellow GP DensGlass gypsum board at right is protecting the …
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.
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A view from underneath a stair landing within a stairwell shows …
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.
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The ceiling of a hallway between the elevator shaft and the gara…
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.
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A view of the underside of a stairwell from the garage level. Gy…
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.
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"There is no plate-to-plate wood connection anywhere in this bui…
"There is no plate-to-plate wood connection anywhere in this building" across the walls separating fire-protected spaces, Rob Paisley explains. Here you can see the special truss hangers used to attach floor trusses, which have a two-inch space so that gypsum board can be slipped between the wall frame and the floor frame.
Ted Cushman/JLC
Ted Cushman/JLC
Ted Cushman/JLC
"There is no plate-to-plate wood connection anywhere in this bui…
"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.
Ted Cushman/JLC
Another look at the specialized truss hangers, which allow wood …
Another look at the specialized truss hangers, which allow wood floor framing to be isolated from wall framing by fire-resistant gypsum board.
Ted Cushman/JLC
As the new building rises up above the roof of the adjacent buil…
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.
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A view along the roof of the older adjacent building toward its …
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.
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The fire-protected stairwell for the new building rises up above…
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.
Ted Cushman/JLC
A view of the new firewall assembly over the rooftop of the neig…
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.
Ted Cushman/JLC
A view of the partially completed firewall as seen over the top …
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.
Ted Cushman/JLC
Contractor Rob Paisley fastens an aluminum breakaway clip to the…
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.
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Paisley attaches the firewall frame to the wood wall of the new …
Paisley attaches the firewall frame to the wood wall of the new building with an aluminum clip.
Ted Cushman/JLC
On a snowy day in spring, the crew constructs the gypsum-board a…
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.
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The crew slips gypsum board into the space between the old build…
The crew slips gypsum board into the space between the old building and the new frame under construction.
Ted Cushman/JLC
The crew slips an H-stud over the edge of the double layer of 1-…
The crew slips an H-stud over the edge of the double layer of 1-inch gypsum board.
Ted Cushman/JLC
Paisley pins an H-stud to the gypsum board with a one-inch screw…
Paisley pins an H-stud to the gypsum board with a one-inch screw.
Ted Cushman/JLC
Paisley places an aluminum breakaway clip.
Ted Cushman/JLC
Screwing the aluminum clip to the steel C-channel.
Ted Cushman/JLC
Paisley screws the breakaway aluminum clip to the stud wall.
Last month, JLC showcased the balcony structure of a new four-unit apartment building in Portland, built on a tight lot with close setbacks (see “Cantilevered Balcony Beams,” JLC 5/16). This month, we’ll take a look at a nearby building under construction that’s not just close to the neighbor—it’s touching it (well, almost).
We talked with contractor Rob Paisley on site during the framing of the new apartment building. The property is sited on a double lot, adjacent to an existing building that dates back to the 1800s.
A recent change in the neighborhood’s zoning allows the developer to build a new four-story structure directly abutting the older house. But while that zoning change was pending, Paisley renovated the existing house. Now, he’s constructing the new building next door.
“When you do that,” Paisley explained, “the new structure has to be completely isolated from the old one.” To accomplish the required fire separation, Paisley and his framing crew built a typical two-hour firewall (in Paisley’s phrase, a “burn wall”) between the two structures as they framed the new building.
Framers attach a ledger for a stair landing to the stairwell shaft wall, after first fastening a strip of GP Gold Bond gypsum board in place at the ledger location. Framing multiple fire-protected elevator and stairwell shafts is tricky when no wood-to-wood contact between the shafts is allowed, observed contractor Rob Paisley. This staircase will help keep the shaft plumb and stable as the walls rise.
This isn’t the only fire-rated wall in the building. The building’s two stairwells and its elevator shaft are each isolated from the rest of the structure with two-hour fire-rated assemblies. That was a challenging problem, said Paisley. “There is no plate-to-plate connection anywhere in this building,” he said. “It literally has to be broken everywhere, which makes this hard.”
With no wood-to-wood connections, keeping the walls straight and plumb has had its own difficulties. And with four occupied floors above the garage level, topped off by a walkable rooftop patio, resistance to lateral loads is also a concern. “This project encompasses every bit of residential and commercial you’d be likely to see in one building,” said Paisley. “It could be a crash course for somebody who has never done it before.”
Paisley beefed up structural assemblies in several places—for instance, adding shearwalls in the garage level and applying structural sheathing to both faces of some wall assemblies. For the wall backing up the two-hour gypsum-panel assembly, Paisley’s crew installed old-school diagonal bracing between the studs.
Working from the roof of the older house next door, Rob Paisley and his crew slip a two-foot by four-foot piece of National Gypsum Shaftliner eXP gypsum board into the space between their new four-story condominium building under construction.
As the new building rose next to the old one, the two-hour fire separation assembly had to be pieced together in between. That’s accomplished using light-gauge-steel H-studs and C-runners, attached to the wood framing with aluminum breakaway clips. The 4-foot-by-2-foot pieces of gypsum board slip into the channels of the vertical H-studs and horizontal C-channels, and are secured lightly to the metal with screws. Then the metal framework is attached to the wood framing of the buildings on either side using the aluminum clips.
Ted Cushman/JLC
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.
The gypsum board is tested to hold up for two hours in the event of a fire, allowing time for occupants of adjacent buildings to evacuate and for firefighters to extinguish the fire. If fire spreads into the wood walls on either side of the firewall (and the assembly works as designed), the heat of the fire will melt the aluminum clips only on the affected side, so that collapsing stud walls on that side would not pull down the firewall.
