Case Files · Risk analysis
The hidden risks of ESP.
Why elevator shaft pressurization can cost you millions in commissioning exposure — and when smoke curtains are the clearer choice.
The critical issue
You don’t know if it works until commissioning day.
After spending $100,000–$300,000+ on installation, you’re hoping that when systems finally come together — with the right weather — elevator shaft pressurization will actually meet code.
15–30%
of ESP systems require remediation during commissioning — weeks of delay and $50,000–$200,000+ in fixes.
The commissioning gamble.
For ESP to work on commissioning day, you need a perfect storm of conditions:
1. All building systems completed and operational
HVAC balanced, facade sealed, doors installed and adjusted.
2. Ideal weather conditions
Specific temperature differential, minimal wind.
3. Perfect building tightness
Every penetration sealed, every door gap within tolerance.
4. Coordinated system operation
Elevator controls, fire alarm, HVAC dampers, and fans communicating correctly.
5. Accurate modeling
Engineer’s calculations captured real-world leakage characteristics.
Miss any one condition = failed commissioning
No certificate of occupancy. Project delays. Cost overruns.
When commissioning fails
Three failure modes.
Over-pressurization (>0.25 in. water column)
Problem: Elevator doors won’t open or require excessive force — a code violation that blocks the occupancy permit.
Run the numbers
Real financial risk.
Same planning model as before — ESP cost, curtain alternative, and a two-month failure scenario.
Interactive · Planning ranges
ESP risk exposure.
Compare ESP install cost to smoke curtains, then model a two-month commissioning failure. Formulas shown below the totals — planning guidance only.
Model vs reality
What engineers model vs what happens.
ESP design calculations typically include 10–20% safety factors. Real-world variance is 50–200%.
| Models assume | What happens | Impact |
|---|---|---|
| Uniform door gaps (1/8" all around) | Door gaps vary 1/16" to 3/8" with install and settling | 100–300% leakage variance |
| Consistent facade leakage per specs | Actual curtain-wall performance varies widely | 200–500% leakage variance |
| All penetrations properly sealed | Trades don’t seal to air-barrier standards | Unpredictable leakage paths |
| Perfect HVAC coordination | Balancing takes months and changes pressure profiles | System performance drifts |
| Standard occupant behavior | Tenants modify spaces, prop doors, add equipment | Requires recalibration |
Bottom line: Hundreds of small deviations from perfect construction cannot be captured in models. You’re designing for an idealized building that doesn’t exist.
Compliance paths
Compare four methods.
Smoke curtains
Advantages
- →Lowest install cost ($4,000–$8,000/floor)
- →Zero commissioning risk — factory tested
- →Weather independent
- →Gravity fail-safe
- →No space consumption
- →Invisible when retracted
- →Simple annual testing
Considerations
- →Annual drop testing required
- →Motor replacement every 20+ years
- →Visible when deployed
Elevator shaft pressurization
Advantages
- →Single system for multiple elevators
- →No space consumption
- →Completely hidden from view
Major disadvantages
- →Unknown until commissioning ($100K–$300K+ at risk)
- →15–30% failure rate requiring remediation
- →Weather-dependent performance
- →Complex maintenance ($3K–$8K/year)
- →Recalibration after building modifications
- →System-wide failure affects all floors
- →Performance drifts over time
Enclosed lobbies
Advantages
- →Completely passive — most reliable
- →No commissioning risk
- →Minimal maintenance
- →Proven 100-year track record
Disadvantages
- →High cost ($20K–$30K/floor)
- →Consumes 50–150 sq ft per floor
- →Lost rental revenue
- →Blocks modern open designs
- →Impedes firefighter access
- →Wayfinding confusion
Swing doors
Advantages
- →Lower cost than lobbies
- →Returns some floor space
- →Simpler than lobbies
Critical problems
- →30–50% found propped open by occupants
- →Bottom seal is a weak point for smoke
- →High maintenance burden
- →Tampering defeats protection
- →Gasket replacement every 5–10 years
- →Industry moving away from this method
Risk-return
Would you take this bet?
ESP system
10:1 to 40:1
RISK RATIO
You’re risking millions in delay costs to save maybe $100K–$200K vs smoke curtains.
Expected value: −$195,000
Smoke curtains
Near zero
RISK RATIO
Pay slightly more upfront for certainty — no commissioning risk, no failure exposure.
Expected value: +$51,900
Best case: save $150,000. Worst case: lose $500,000–$4,000,000 in delays plus retrofit. Failure probability: 15–30%.
Of course you wouldn’t take that bet with your own money. Yet ESP is still specified on outdated assumptions.
By building height
Recommendations.
Primary: avoid protection requirements where code allows
Ensure full NFPA 13/13R sprinkler protection in non-institutional occupancies to eliminate hoistway protection for buildings connecting ≤3 stories.
If a 4th story triggers requirements:
- → New construction: enclosed lobbies often most cost-effective
- → Retrofit: smoke curtains excel
- → Never use ESP — complexity unjustifiable at this scale
Exception: institutional occupancies (I-1 Condition 2, I-2, I-3) require protection regardless of height — smoke curtains optimal.
Industry incentives
Why this isn’t discussed openly.
| Stakeholder | Incentive | Why they don’t warn you |
|---|---|---|
| MEP engineers | Design fees from complex systems | Once designed, commissioning failure becomes “contractor’s problem” |
| General contractors | Build what’s specified | Commissioning issues generate lucrative change orders |
| Commissioning agents | Paid to troubleshoot | System failures mean more billable hours |
| Owners (who’ve been burned) | Reputation protection | Don’t publicly advertise expensive project failures |
The people who could warn you don’t write the specifications.
Bottom line
What should you do?
Under 20 stories
Specify smoke curtains.
ESP should be disqualified on commissioning-risk grounds alone. Financial exposure from uncertainty exceeds any install savings by 10–40×.
Over 20 stories
ESP only if every condition is met.
- → Experienced ESP commissioning team
- → 6–8 week post-completion buffer
- → $100K–$200K troubleshooting contingency
- → Weather-independent commissioning protocol
- → Clear remediation responsibility in the contract
Otherwise, smoke curtains remain the prudent choice for risk-averse owners.
Retrofit — any height
Smoke curtains. No exceptions.
Minimal structural work, floor-by-floor install in occupied buildings, contained costs — no wholesale shutdowns.
Next step
Don’t gamble the C of O.
Ask for a project-specific risk read — usually same-day.
john@thesmokecurtainguy.com