Basis: Virtuoso "Studio and One-Bedroom Expansion" prelim set (2021, not for construction), scaled off the 5' bar. Ken's answers, 6 Sep 2026. Hand estimates only — for the model and for the PE conversation, not for construction.
1. Project facts (stated)#
| Item | Value |
|---|---|
| Location | Jamaica — hurricane wind region, no snow |
| Bearing walls | 3D-printed concrete walls |
| Roof membrane | Spray-applied (Eco Finish industrial coating) |
| Footprint (studio, scaled) | ~25' wide (grid 1–2) × ~21' deep (grid A–B) |
| Stud direction | Span the 21' dimension (A to B) |
| Studs | 6" CFS, gauge to be proposed |
| Channel | 1-1/2" cold-rolled channel run horizontally under the stud bottom flanges, screwed up into the studs; punchouts left open for concrete flow and conduit |
| Reinforcement | Basalt mesh sandwiched between stud bottom flange and channel (spec TBD) |
| Layer stack (form up) | 2" concrete cover → 1-1/2" channel + mesh → 6" stud cavity → 2" cap = 11.5" total |
| Ground pour | 6.5" (2" cover + 1.5" channel zone + 3" into the stud) |
| Top pour (on roof) | 5" (remaining 3" of cavity + 2" cap), slight slope to drain |
| Midspan bearing | Yes — printed interior wall or beam near grid 3; studs span ~10.5' each side |
| Cellular concrete | 30–40 pcf |
| Panels | One panel per roof if possible, two if not; cast-in pick points |
| Cure before pick | 7 days |
| Engineering | PE to be engaged later (Ken has one in mind) |
2. Loads (hand estimate, 35 pcf)#
| Load | psf |
|---|---|
| Cellular concrete, 11.5" @ 35 pcf | 34 |
| Steel (studs, track, CRC, inserts) | 4 |
| Membrane / misc | 1 |
| Dead | ~39 |
| Roof live (min) | 20 |
| Slope build-up if 1/8"/ft over 21' (extra ~2.6" at the high edge, avg 1.3") | +4 avg |
| Total gravity for sizing | ~60–65 |
Wind: hurricane-region flat roof. Net uplift at corners/edges routinely exceeds 0.6 × dead even at 34 psf dead. Anchorage to the printed walls is a design item, not a detail — see §5.
3. Span — the governing issue#
At 16" o.c., 21' clear span, ~60 psf:
- Moment ≈ 53 kip-in per stud. A 600S162-68 (14 ga, 50 ksi) is roughly 42–45 kip-in allowable → over.
- Deflection ≈ 4.2" single stud → ~L/65. Limit for a concrete-topped roof is L/240 or tighter (≈1.05").
- The cellular concrete does not help: at 30–40 pcf it is
200–500 psi with negligible stiffness. Steel carries everything; concrete is fill, insulation (R-1.5/in → ~R-17 total), and ceiling.
A 6" CFS stud cannot clear-span 21' under this roof. Three ways out:
| Option | What changes | Stud proposal |
|---|---|---|
| A. Midspan bearing (preferred if the printed wall layout allows) | Add a printed interior bearing wall or a steel beam at ~10.5' (near grid 3 / the bath–kitchen wall line) | 600S162-54 @ 16" works with margin (≈L/400); use 600S162-68 @ 16" for screw pull-out and hurricane robustness |
| B. Deeper joists, keep the concept | Stud depth 10" | ~1000S200-97 @ 16" clears 21' (≈L/290); panel gets ~4" thicker and ~12 psf heavier |
| C. Keep 6", double/box and tighten spacing | 12" o.c., boxed pairs | Still marginal on deflection; not recommended |
Option A keeps the 6" system exactly as Ken described. The animation should model A as the default with B as a config switch.
4. Panel at pick (Option A, one panel)#
| Item | Value |
|---|---|
| Panel plan size | ~25' × 21' (525 sf) plus edge forms |
| Concrete at pick | 6.5" @ 35 pcf ≈ 19 psf |
| Steel | ~4 psf |
| Pick weight | ~12,000 lb (+ lifting frame) |
| Crane | Mid-size hydraulic (40–60 t class depending on reach); cast adjacent to the building |
| Pick points | 8 cast-in inserts on stud lines, 2 rows at ~0.2L from each end, spreader frame so all legs are vertical |
| Cracking risk | 7-day cellular concrete in a 2" layer under a flexing steel frame. Basalt mesh helps; the real control is a stiff spreader frame and keeping frame deflection under ~L/360 during the pick. PE to check |
| Two panels | 12.5' × 21' each ≈ 6,000 lb — fallback if crane access is tight; joint runs parallel to studs at grid 3 |
5. Interfaces to detail#
- Wall top: cast a bond beam on the printed wall with embedded plates or anchor bolts. Panel bears on a continuous track; weld or bolt track to embeds. Uplift straps/anchors at each stud line at edges and corners.
- Edge of panel: closure track or angle so the top pour doesn't run over the wall; the spray membrane turns down over it.
- Ceiling: 2" cellular concrete under the studs is the finished ceiling (one skim coat max). Mesh should sit ~1" from the bottom face for crack control.
- Top pour: 2" minimum cap over studs; build slope in the cap (1/16–1/8"/ft) toward scuppers or a drain edge. Second mesh layer in the cap if the PE wants it.
- Penetrations: sleeves for plumbing vents and electrical set in the form before the ground pour.
6. Open items for Ken / the PE#
- Channel-to-stud screw pattern and spacing of channel rows (the channel now carries the 2" ceiling layer and the mesh; the PE will want to see the fastener count).
- Exact position of the midspan bearing line relative to the interior wall layout.
- Basalt mesh spec (grid, weight, layers).
- Design wind speed / exposure the PE will use (Jamaica NBC adopts ASCE 7-style loads).
- Cellular concrete supplier mix (density, 7-day and 28-day strength).