For a 45-story office tower around 1.1M sf GFA, are you getting better net-to-gross with a sky lobby + shuttles or by just beefing up low/high-rise banks? On our last 38-story we lost about 14% to VT and cores, and I’m trying to keep this one tighter without killing wait times.
I’ve seen a single sky lobby around 23 with 6–8 shuttles feeding two 8‑car zones beat a straight low/high bank by roughly 1–1.5% core on a 45‑story about 1.1M sf, but it falls apart if ‘interfloor >10%’ because transfers sting. Quick step: mirror your last building’s 5‑min handling and 80th‑percentile wait targets in a sim and toggle a double‑deck shuttle; CTBUH has a few case studies: https://global.ctbuh.org/resources/elevators. @OP curious what your expected interfloor share and peak design density are.
On a transfer level + shuttles setup, skew the split so the heavier lower floors have a shorter zone, spec about 1,400 fpm shuttles and tighten door times (30–35 s), and make the transfer level a “pit stop” with amenities — I’ve seen that claw back about 1–2% core versus fatter low/high banks. @liamill’s point is solid, but if you expect lots of inter-floor trips or 3–5 floor stacks, a through-served mid zone with destination dispatch can beat transfers on user feel even at a small core premium. What peak 5‑min handling and average wait are you targeting?
If your AHJ allows it, consider two cars in one shaft (TWIN); on a 45‑story about 1.1M sf we clawed back about 1–1.5% net vs a transfer setup and eliminated two shafts without wrecking waits. Caveat: capex and code path can be an , but it beats your ‘14%’ hit — @OP would your AHJ allow TWIN, or a small double‑deck zone on the busier lower floors? Page not found.
We shaved about 0.8–1.0% core by running a short double‑deck low zone (L1–18) into a single transfer at 20, keeping the upper zone single‑deck, and stacking the transfer with the refuge/mech floor to keep the lobby off rentable corners. Building on @sophia5187’s timing note, tune the DD door cycles separately from the shuttles — would your AHJ allow a limited double‑deck just in the low zone?
I’d squeeze area by right‑sizing cars and door openings before adding a sky lobby. If most passenger cars stay 3,500 lb with 42" doors and a single 48" stretcher car per bank, you typically shave about 4" off shaft width and about 3–4" off depth — roughly 200–300 sf per floor across 10–12 shafts — while destination dispatch preserves the “tighter without killing wait times” goal. Caveat: verify stretcher requirements with the AHJ and queuing clearances; what door width are you carrying now?
Skip the transfer unless you can monetize that floor; on a 45‑story about 1.1M sf, destination dispatch + unequal group sizing and required interconnecting stairs for 2–3 floor tenants cut peak enough to drop a car and trim about 0.8–1.2% from core. I’m with @sophia5187 on right‑sizing, but DD + interconnects moved the needle more than a sky lobby for us. What’s your up‑peak target and how much inter‑floor traffic are you carrying off the 38‑story that landed you at “14%”?
Leaning sky lobby only if you can stack it with the required refuge/mech level and monetize that floor; otherwise you’ll lose more in transfer area than you save in shafts. On a about 45‑story about 1.1M sf with your “14% to VT and cores,” I’ve clawed back about 0.5–0.8% by upping car speed one notch (e.g., 1200→1400 fpm) and widening the mid‑zone so one fewer shaft serves the stack, sanity‑checked in Elevate. Quick ref: CTBUH VT planning envelopes are here https://global.ctbuh.org/resources/.
And , watching 14% disappear on a 38‑story hurts. Building on @brad_taylor99, if your AHJ will approve two independent cars in one shaft (TKE TWIN), you can often drop 2–3 shafts and avoid a transfer floor while keeping waits acceptable; we clawed back about 1.5–2% net‑to‑gross on a 46‑story that way, but egress modeling and controls sign‑off were the sticking points. Does your jurisdiction allow TWIN or are you limited to single cars/double‑deck?