SLTNS Engineered Systems®

We bring the SLTNS®. Smoke control, A2L leak detection, fire-rated ducts & dryer exhaust systems - repped right. 🔥

[SLTNS Engineered Systems® @SLTNSengsys]

Architecture firms are still grinding through one of the longest downturns on record.

June’s Architecture Billings Index came in at 47.3 — a solid nearly 3-point climb from May, but still below the critical 50 mark. That means the majority of firms continued to report declining billings.

A few bright spots: project inquiries jumped to 56.1 and design contracts held essentially flat at 49.8. Backlogs, however, edged lower to 6.3 months, with the smallest firms (under $250k) seeing the sharpest drop — from 4.9 months down to just 3.1.

Regional picture:
South led at 49.5
West 45.6 | Midwest 45.1 | Northeast 44.9

Sector view:
Institutional 47.4
Commercial/Industrial 46.7
Multifamily Residential 45.6
Mixed Practice 42.7

The rebound is taking its time. Pipelines remain thin and competition is intense.

What are you seeing out there in your markets?

[SLTNS Engineered Systems® @SLTNSengsys]

Architecture Billings Weaken Further in May

The AIA/Deltek Architecture Billings Index fell to 44.5 — its lowest since January — as economic uncertainty slows projects.

Billings declined across all regions: South (49.6), Northeast (46.2), West (45.4), and Midwest (45.3). All sectors also saw declines, with inquiries dropping below 50 and new design contracts weakening.

Elevated interest rates, rising material costs, and labor shortages are weighing on demand.

Key signal for the building industry as early-stage design activity cools.

[SLTNS Engineered Systems® @SLTNSengsys]

As states or AHJs legalize egress reforms, let's make sure the fire safety engineering keeps pace.

Scissor stairs share a single shaft. The fire-rated center wall only works if you maintain a positive pressure differential across it. On taller buildings, that requires active compensated stairway pressurization — not just a constant-volume fan that fails the moment doors open during evacuation.

Legalize the design. Specify the system that makes it survivable. Both can happen at once.

[SLTNS Engineered Systems® @SLTNSengsys]

"Pressurization" is doing a lot of heavy lifting there. What kind?

A constant-volume fan can't maintain the required pressure differential when doors open during evacuation. ASHRAE RP-1447 proved this — even a single open door can drop pressure below the IBC 909.6.1 minimum. Multiple doors open at once and the system fails entirely.

"As safe as physically possible" is active compensated multipoint injection — a UL 864-listed controller modulating fan speed and, if necessary, the relief damper in real time, maintaining pressure across the full height of the stair regardless of door conditions.

Fire rating is the foundation. Active compensation is what makes it perform.

[SLTNS Engineered Systems® @SLTNSengsys]

Not true. Fire-rated walls and self-closing doors are necessary — but not sufficient.

Smoke migrates toward stairwells driven by stack effect, buoyancy, and wind. These forces generate pressure differences that push smoke through construction cracks, gaps around closed doors, and every leakage path in the barrier. IBC 909.5 even defines maximum allowable leakage area ratios for smoke barriers — because no wall or door assembly is airtight.

And during evacuation, those self-closing doors aren't closed. They're being held open by a stream of people escaping the building. ASHRAE RP-1447 showed that opening even a single stairwell door can drop the pressure differential below the minimum needed to keep smoke out. Open several doors at once — which is exactly what happens during evacuation — and the pressure difference collapses entirely.

Passive barriers buy time. Active compensated stairway pressurization maintains the positive pressure differential that actually keeps smoke on the other side of that fire-rated wall — in real time, under real conditions, with doors opening and closing unpredictably.

Walls don't pressurize themselves.

[SLTNS Engineered Systems® @SLTNSengsys]

Everyone's celebrating scissor stairs. Nobody's talking about the engineering that makes them survivable.

Scissor stairs share a single shaft. If smoke enters one stairway, only a fire-rated wall separates it from the other. The most certain way to keep smoke out? A multipoint injection system monitored and controlled by LF Systems' Active Compensated Stairway Pressurization (ACSP).

IBC 909.6 requires positive pressure differentials across smoke barriers — min 0.05" w.g., max limited by door-opening force. A constant-volume fan can't hold that range. When doors open during evacuation, pressure drops instantly. When they close, it spikes. No feedback means no control.

ASHRAE RP-1447 (NRC Canada full-scale fire tests) proved it: opening even a single stairwell door can drop pressure below the minimum. With multiple doors open near the injection point, single-injection systems fail entirely — pressurization air escapes through the openings. The SFPE Handbook and ASHRAE Handbook of Smoke Control Engineering confirm that single injection systems for stairwells over 100 ft can fail when a few doors open simultaneously.

The solution is multipoint injection with active compensation: the ACSP's UL 864-listed L864 controller continuously compares stairwell-to-floor pressure using multiple transducers. Doors open → fan speed increases. Doors close → output reduces, relief damper opens. Real-time feedback keeps pressure in the code-required band — regardless of stack effect, wind, or door conditions.

For taller scissor stair buildings, injection point regulators at each zone provide zone-by-zone pressure control through modulating dampers, or individual fan controllers at each injection point — not guesswork.
And per IBC 909.12, the smoke control system controller MUST be UL 864-listed. A BAS, PLC, or standalone VFD is a code violation unless it carries that specific listing.

Legalizing scissor stairs is a win for housing. But a scissor stair with a constant-volume fan is a liability waiting for a fire. Active compensated multipoint injection pressurization is the most certain method to ensure these stairs perform when lives depend on it. Build smarter AND safer.

[SLTNS Engineered Systems® @SLTNSengsys]

We honor those who made the ultimate sacrifice in service to our country and for our freedom.

Memorial Day is not just a long weekend — it’s about gratitude, remembrance and reflection. As we spend time with family and friends, let’s also take a moment to recognize their courage and selflessness. 

Our offices will be closed on Monday, May 25, in observance of the national holiday.

#MemorialDay

[SLTNS Engineered Systems® @SLTNSengsys]

📉 Architecture Billings Index (ABI) slipped to 48.3 in April from 49.8 in March, with billings remaining below the 50 growth threshold since January 2023.

All regions stayed in contraction:
- West: 49.0 (least negative for 3rd straight month)
- Midwest: 48.0
- South: 47.7
- Northeast: 47.2

Positive developments in key sectors: Multifamily residential (51.5) and institutional (51.1) posted modest growth, while commercial/industrial (48.9) continued to decline. Mixed-practice firms remained weakest at 42.5.

New project inquiries rose for the third consecutive month, and the value of new design contracts is approaching growth territory again.

[SLTNS Engineered Systems® @SLTNSengsys]

No problems, only SLTNS®… even on the track! 🏁

Car #54, our sponsored FG2 Civic Coupe and backup car, competed in two 8-hour American Endurance Racing events at Watkins Glen International on May 2nd & 3rd, earning a podium with a 3rd-place class finish on Saturday and fighting hard to secure 8th in class on Sunday.

Huge congrats to the entire SLTNS Racing Team on an incredible weekend! 🏆

Next up: Summit Point in June. See you at the track!

#americanenduranceracing #watkinsgleninternational #watkinsglen #WGI

[SLTNS Engineered Systems® @SLTNSengsys]

NYC's new A2L refrigeration safety standards take effect May 15th. The rule adopts ASHRAE 15-2022 and introduces ventilated shaft requirements that will impact multi-story buildings across the city. Is your team ready? @NYC_Buildings #A2L #ASHRAE15 #NYC #RefrigerationSafety

[Chimney Design Solutions® @chimneynet]

NYC Adopts New Safety Standards for A2L Refrigerants — Effective May 15, 2026

The NYC Department of Buildings has adopted new rules relating to Safety Standards for Refrigeration, adding four new sections to Chapter 7000 of Title 1 of the Rules of the City of New York. Driven by Local Law 77 of 2023, this rule aligns the city's Mechanical Code with the transition to lower-GWP A2L refrigerants like R-32 and R-454B.

The rule formally adopts ASHRAE 15-2022 as the governing standard for A2L systems, establishing requirements for refrigerant detection, mitigation actions, prohibited piping locations, machinery room ventilation, and pipe shaft enclosures, including the requirement that refrigerant piping penetrating two or more floor/ceiling assemblies be enclosed in a fire-resistance-rated, ventilated shaft. That provision alone carries significant design and construction implications for multi-story buildings across the city.

Engineers, contractors, and building owners in NYC: this takes effect next month. If you haven't reviewed these requirements yet, the clock is ticking. We offer an accredited lunch & learn, "A2L Refrigerant Line Shafts: Ventilation & Enclosure Requirements," approved for continuing education credit in FL, MD, NJ, & NY. Reach out to schedule one for your team. Full rule details linked in the comments.

#A2LRefrigerants #ASHRAE15 #NYC #NYCMC #LL77 #AIMact #R454B #R32

[SLTNS Engineered Systems® @SLTNSengsys]

ASHRAE 15-2024 Addendum A allows you to skip the shaft if the refrigerant piping passes a pressure test per Section 9.13. But, before you remove the shaft from your drawings, consider these three key points:

1. The 2024 IMC does not recognize Addendum A.

The 2024 International Mechanical Code references ASHRAE 15-2022 – not 2024. Section 1109.3.2 (or equivalent in adopted versions) requires a ventilated shaft for refrigerant piping in many cases. Addendum A currently has no legal standing under the IMC.

2. Most AHJs aren’t accepting Addendum A.

Even in jurisdictions referencing ASHRAE 15-2024, adoption of Addendum A varies widely (some AHJs may approve alternatives case-by-case, but many don't). Designing around it risks code rejection and costly late-stage redesigns.

3. Addendum A does not apply to A3 refrigerants.

A3 refrigerants (e.g., R-290/propane) require continuous mechanical ventilation and detection – no shaft exemption applies here. If your client's building might transition to A3 refrigerants in the future, the shaft needs to stay in the design regardless.

And here's the real question: If a refrigerant pipe leaks 10 years from now without a shaft, where does the refrigerant go?

A pressure test only proves the piping is leak-free at the time of testing. It doesn't guarantee long-term integrity through thermal cycling, building settlement, vibration, or service work over decades.

[SLTNS Engineered Systems® @SLTNSengsys]

Is the three-year slide in architecture billings finally bottoming out?

March's AIA/Deltek ABI came in at 49.8 — the closest read to the 50-point growth threshold since early 2023. Just as important, the sectors that drive commercial construction are already expanding:

• Institutional: 52.6
• Commercial/Industrial: 52.5
• Multifamily Residential: 50.9

Inquiries jumped to 56.8. Backlogs now average 6.6 months, the highest in over two years. Multifamily backlogs in particular have grown nearly a full month since December.

The caveats are real: design contracts are still contracting (47.8, now 25 straight months), the Northeast remains soft at 44.2, and AIA itself flagged labor shortages and geopolitical risk as meaningful headwinds.

But for AEC firms planning headcount, capacity, and pipeline for H2, this is the first month in a long time that the signal points up.

[SLTNS Engineered Systems® @SLTNSengsys]

Size your A2L shaft ventilation system in 60 seconds.

Enter your pipe circuits, insulation, and clearance — the tool calculates shaft dimensions, selects the right fan, generates a CSI Section 23 09 23 spec, and produces a branded PDF report.

→ https://t.co/uyoVGiCLr7

[SLTNS Engineered Systems® @SLTNSengsys]

Shaft ventilation isn't the only compliance path being discussed.

ASHRAE 15-2024 Addendum A introduces an alternative for branch box applications — but only if your local AHJ permits its use. Not all will.

PurgeSafe™ is being developed to support branch box applications as well.

More details coming soon.

[SLTNS Engineered Systems® @SLTNSengsys]

R-290 (propane) is already in commercial refrigeration and moving into HVAC.

Under both the 2024 IMC §1109.3.2 and ASHRAE 15-2022 §9.12.2.2, A3 refrigerant shafts must be continuously mechanically ventilated with a refrigerant detector.

No natural ventilation option. No shaft alternative. No exception.

PurgeSafe™ can be equipped with sensors to detect A3 refrigerants.

Design the future-proof shaft now.

[SLTNS Engineered Systems® @SLTNSengsys]

A refrigerant leak in a shaft shouldn't be a silent event for building management.

PurgeSafe™ sends alerts to your BMS via Modbus RTU/TCP or optional BACNet the moment a leak is detected.

Facility managers know. The system responds. Occupants are protected.

Full visibility. Fully integrated.

[SLTNS Engineered Systems® @SLTNSengsys]

When a refrigerant leak is detected, the last thing you want is the compressor continuing to run.

PurgeSafe™ includes a compressor interlock that shuts down the VRF system the moment a leak is confirmed.

Less refrigerant loss. Less exposure. Less risk.

Detection without interlock is half a solution.

[SLTNS Engineered Systems® @SLTNSengsys]

IMC §1109.1 requires periodic testing of mechanical shaft ventilation systems.

PurgeSafe™ handles it automatically.

Every 30 days, the system runs a self-test — verifying fan operation, damper function, and sensor performance.

No manual testing. No scheduling. No forgetting.

Compliance built in.

[SLTNS Engineered Systems® @SLTNSengsys]

PurgeSafe™ is compliant with ASHRAE 15 and the 2024 IMC.

Available in six configurations from 430 to 5,660 CFM — for shafts of virtually any size.

Detect. Ventilate. Protect.

[SLTNS Engineered Systems® @SLTNSengsys]

A2L refrigerant leaks are invisible and odorless. They accumulate silently — at floor level, across multiple floors, with no warning.

A properly designed shaft changes every one of those outcomes.

Here's how PurgeSafe™ works. 🧵

[SLTNS Engineered Systems® @SLTNSengsys]

Built-in monthly self-testing automatically verifies fan, damper, and sensor operation.

Satisfies IMC §1109.1 — no manual testing required.

The system proves it works before you need it to.