I’m going to work for Salmond Reed over the summer. Knowing that I love to have a dekko at an old building with the covers off, Tracey Hartley from SR very kindly invited me along to a site visit she was making to the Pitt St Buildings. A brief post, then, to share with you a couple of details from the project.
The main aim of the work at Pitt St is to replace the roofs and restrain the parapets. The parapets are large, ornate and slender. They needed thorough bracing, but that bracing had to be as unobtrusive as possible. The original design was a conventional diagonal bracing approach, but that was too obvious from the street and created future roof maintenance problems. Following close collaboration between the architects and the engineer, a design was developed that not only met the seismic strengthening requirements but also was acceptable aesthetically for this important 5th elevation of the building. Most of the braces and their triangulated members have been tucked under the roofs and exposed steelwork minimised to the gables. At the bottom left edge of the picture above you can see a hatch—I ducked though it to have a look at the rest of the brace.
Draining the pool
Designing efficient water run off is part of Tracey’s expertise. She’s developed an instinct for understanding how water flows through and over a structure. My photograph below doesn’t show quite the right angle, but Tracey explained that she’d advised on the design of the connections between the bracing and the parapet, to avoid potential water traps. For example, the C-section channels that run horizontally are packed out slightly from the wall, allowing water to run behind them without getting trapped.
On our way to look at another part of the roof, we passed by a beautiful piece of crafting—a welded-lead cap connecting the new stainless-steel gutter with the existing downpipes. This nifty improvisation is the work of Chris the artisan plumber.
Moving to the Pitt St/K Road corner of the building, we inspected the timber and steel components of the new roof. The roof has been altered from its original profile: it now has a central gutter, instead of sloping right down to the back of the parapet. Keeping the water away from the brickwork protects better against intrusion.
The repositioning of the gutter at this corner section also serves a structural purpose: the short rafter members that go from the gutter to the parapet are also tying the parapet back to the steel beam that runs around the corner section. The timber running along just below the top of the parapet is fastened into the brick. As you know, attentive reader, this kind of heritage-structure win-win design is catnip for me.
All the water on that roof has to go somewhere. In this case, the gutter leads to a smallish aperture in the rear gable wall called a corner sump outlet. Tracey wanted to make sure that the water would pass through the outlet, visible in the picture below, without backing up, overspilling, getting behind the lead flashings (the grey step-shapes on the right) or exerting too much pressure on the outer wall.
In the end, the solution she devised with Adam the project architect and René the contractor was to increase the fall somewhat, and form a stainless-steel sump box before the hole. The increased fall makes the choke-point a bit larger, and the tank protects the surrounding fabric if water backs up at this point. This is the kind of on-the-fly rethinking that takes decades of experience to spot and to remedy. The author (somewhat uncharacteristically) kept his trap firmly shut.
Passing around the corner to the Pitt St side of the building, we saw more re-roofing and parapet work. There was no angle to photograph it from, but it was possible to peek under the bottom of the timber roof sarkings that you see in the photo above. Underneath were more steel parapet braces—these ones appeared to be long straight members, concealed entirely under the roofs. They have to be long because they can only rise at a shallow angle under the small roof spaces. As at the corner section, these braces connect to a longitudinal beam.
Tracey, Adam and Chris worked on a plan to connect the gutters of the new roofs to the existing Colorsteel™ gutters on the parts of the building that sit behind this section—to the right, in the picture. They settled on a plan that involved joining the new stainless steel and the old Colorsteel™ on the vertical section of a step (the riser, as it were), as opposed to joining it on the flat, where water could pool at the joint. The plan also involved overlapping new and old materials for some distance below the joint. Pernicious stuff, rainwater.
Do have a look next time you’re going along K Road. The project is also going to involve repairing the awning—Heritage Society regulars will remember both Peter Boardman and Jason Ingham talking about how strong awnings protect passers-by from falling parapets. Hopefully, the newly-strengthened parapet won’t tumble, but if it did, you’d be grateful that the ties were in better nick than this.
Thanks very much to Tracey, René, Chris, and Adam for letting me have a look. More soon—two site visits coming up in the next two weeks. Registration links at the top of the page if you’re keen.