Architectural Economics, Circular Construction & Lifecycle Costing
Habraken Open-Building Support vs Infill Lifecycle Cost
Compare John Habraken Open-Building Decoupled Support + Modular Infill Cumulative Lifecycle Cost against Entangled Monolithic Renovation Tear-Out Penalties, Circular Demolition Savings, and Annualized Cost.
Eliminate destructive gut-renovation penalties by decoupling Base-Building Support from Tenant Infill!
Architect John Habraken’s Open Building (SAR) methodology—and Stewart Brand’s "Shearing Layers"—separates long-lived shared structural Base-Building "Support" (columns, slabs, facade, risers; 75–100 yr life) from short-cycle Tenant "Infill" (demountable partitions, raised-floor MEP, fit-out; 12–15 yr churn cycle)! In conventional entangled construction—where conduits are cast into slabs and drywall is glued across structural services—every subsequent tenant churn cycle N_rep = (Horizon_Yrs / Infill_Cycle_Yrs) - 1 incurs a Demolition & Entanglement Tear-Out Penalty p_demo (typically +25%–40% extra cost to jackhammer, haul waste, and patch base systems)! Decoupled Open Building replaces modular infill cleanly at 1.0x cost, saving N_rep * Infill_Capex * p_demo over the building’s life!
Verify on a 75-Year Adaptive Mixed-Use Tower—Base_Support_Capex = $30.00M (B2), Modular_Infill_Capex = $12.00M per fit-out (B3), Tenant_Infill_Churn_Cycle = 15.0 years (B4 -> 5 total infill generations = 1 initial + 4 replacements over a 75-year horizon), Monolithic_Entanglement_TearOut_Penalty = 0.35 (35%, B5), and Study_Horizon = 75 years (B6): Decoupled Open-Building 75-Year Cost is 30 + (5 * 12) = $90.00M (E2); Entangled Monolithic 75-Year Cost is 30 + 12 + (4 * 12 * 1.35) = 42 + 64.80 = $106.80M (E3); Circular Decoupling Savings equal $16.80M (E4); and Annualized Open-Building Capex is 90 / 75 = $1.20M/yr (E5)!
| Open-Building Lifecycle Metric ($30M Support, $12M Infill, 15-Yr Cycle, 35% Penalty, 75 Yr) | Formula | Verified Output |
|---|---|---|
| Open-Building 75-Yr Cost ($M) | Support + Infill * (Horizon / Cycle) | $90.00M ($102.00M @ 12.5-Yr Churn) |
| Entangled Monolithic 75-Yr Cost | Support + Infill + N_rep*Infill*(1+p_demo) | $106.80M ($123.00M @ 12.5-Yr) |
| Decoupling Tear-Out Savings ($M) | Monolithic_Cost - OpenBuilding_Cost | $16.80M ($21.00M @ 12.5-Yr) |
| Annualized Open-Building ($M/yr) | OpenBuilding_Total_Cost / Horizon_Yrs | $1.20M/yr |
Habraken Open-Building vs Entangled Lifecycle Savings Formula
Validate Support_Capex > 0, Infill_Capex > 0, 0 < Infill_Cycle <= Horizon_Yrs, and non-negative Tear-Out Penalty p_demo!
=LET(sp_c, B2, in_c, B3, cy_y, B4, dm_p, B5, hr_y, B6, IF(OR(sp_c <= 0, in_c <= 0, cy_y <= 0, cy_y > hr_y, dm_p < 0), "Invalid Building Lifecycle Input", LET(n_cy, hr_y / cy_y, ob_t, sp_c + n_cy * in_c, mn_t, sp_c + in_c + (n_cy - 1) * in_c * (1 + dm_p), ROUND(mn_t - ob_t, 2))))Accelerated 12.5-Year Tenant-Churn Sensitivity Check
Shorten Infill_Churn_Cycle B4 from 15.0 years to 12.5 years (6 infill cycles = 5 replacements over 75 years): Open-Building Cost E2 is $102.00M vs $123.00M Monolithic in E3, expanding Decoupling Savings E4 to $21.00M!
=IF(ISTEXT(E4), E4, ROUND(E2 / B6, 2))Try the example
Use the original values or change them to test your understanding.