This article explains what those codes are telling you, why “EN12101-2 compliant” is not a complete specification on its own, and what to include in a smoke vent schedule so you do not end up in a long email chain of follow‑up questions.
Why this guide exists (based on real enquiries we receive)
Most first‑messages we see contain one or more of the following phrases:
- “EN12101-2 compliant – can you send the certificate?”
- “We need 1.0m² free area.”
- “What’s the aerodynamic free area / Aa?”
- “Do we need wind deflectors?”
- “Which control panel do we need?” (often meaning parts of the EN 12101 series outside Part 2)
Those are reasonable questions. The issue is that the information needed to answer them properly is often missing. A good schedule prevents avoidable RFIs.
What is usually missing from the initial enquiry:
- The required class set (RE / SL / WL / T / B) rather than a simple “yes/no compliant”.
- Whether the vent is smoke-only or also intended for daily/comfort ventilation (which changes what reliability evidence you should request).
- Whether performance should be based on geometric free area or aerodynamic free area (Aa).
- Whether wind deflectors are permitted (and whether the aerodynamic area is being scheduled with or without them).
- Project exposure inputs for loads: roof snow load and wind load basis (typically given by the structural engineer in kN/m²).
BS EN 12101-2 in 90 seconds: what it covers (and what it doesn’t)
BS EN 12101-2 is the product performance standard for natural smoke and heat exhaust ventilators (NSHEVs) – often called smoke vents or AOVs. In practice, it is used to declare performance characteristics such as reliability, environmental load resistance and temperature capability.
Important coordination point: BS EN 12101-2 is about the ventilator. Controls, power supplies and system components are typically addressed in other parts of the EN 12101 series. That is why “Which control panel is required?” can be a separate discussion from the ventilator’s RE/SL/WL/T/B rating.
If you are looking for product options, start here: AOV Smoke Vents (category).
Quick decoder: what RE, SL, WL, T and B actually mean
Use the table below to translate datasheet codes into practical specification questions.
Code |
What it relates to |
What you should confirm in the project |
Common pitfall (what causes delays) |
|---|---|---|---|
RE |
Reliability class (opening function) |
Is the vent smoke-only, or dual-purpose (daily/comfort ventilation as well)? |
Assuming “EN12101-2 compliant” covers heavy daily use (it doesn’t — you need evidence of the additional dual-purpose comfort cycling, often referenced as 10,000 cycles). |
SL |
Snow load class |
What snow load basis applies to the roof zone? Ask the structural engineer for values in kN/m² (e.g. 0.8 kN/m², 1.5 kN/m²). |
Leaving SL unspecified until submittal review, then needing a redesign or product change. |
WL |
Wind load class |
What wind exposure / roof zone assumptions apply? Again, confirm with the structural engineer and project wind strategy. |
Scheduling the vent before wind exposure and restraints are agreed. |
T |
Low ambient temperature class |
Project climate and roof exposure. External roofs often need a defined low-temperature capability. |
Overlooking temperature class until commissioning or winter callouts. |
B |
Resistance to heat class |
Fire strategy expectations for the ventilator’s heat exposure performance. |
Assuming every smoke vent has the same B class without checking the declared performance. |
RE: Reliability (fire cycles) vs comfort ventilation cycles (dual-purpose)
This is one of the most common points of confusion in real projects.
- RE (e.g. RE 1000) is the fire reliability classification.
- Some smoke vents are also used for daily/comfort ventilation (for purge, airflow, or routine opening). In those cases, you should request evidence of additional comfort ventilation cycling separate from the RE fire cycles.
Example: Surespan’s SRHP/AOV performance block references Reliability 1,000 + 10,000 Comfort, and the SRHPAOV test results table lists RE 1000 with an additional note referencing 10,000 comfort ventilation cycles. Treat these as distinct declarations: RE 1000 relates to fire function; the comfort figure relates to dual-purpose use.
Specifier takeaway: If the building will use the vent for daily ventilation, write that into the schedule and request the comfort cycling evidence alongside the BS EN 12101-2 classification.
SL and WL: choose ratings based on roof exposure (not guesswork)
Most projects do not fail because someone “forgot BS EN 12101-2”. They fail because the submittal does not match the building’s real roof conditions.
What to do:
- Ask the structural engineer for the roof zone design basis for snow and wind (values are typically expressed in kN/m²).
- Set the minimum SL and WL classes in the smoke ventilation schedule using those inputs.
- Select a ventilator that declares those classes in the configuration you are actually installing (including deflectors, opening geometry and any access features).
T: Low ambient temperature class
The T class is easy to miss because it looks like a small detail on a datasheet. In practice, it can become a major snag during sign‑off if the project team never agreed the low-temperature requirement.
Example: SRHPAOV data shows a low ambient temperature classification of T(-15) as part of the BS EN 12101-2 performance set (check the model and current datasheet used for your submission).
B: Resistance to heat (commonly seen as B300)
B is the resistance-to-heat classification. You will often see this scheduled alongside the other key classes (RE/SL/WL/T). If your fire strategy or approving body expects a specific B class, make it explicit in the schedule.
Example: SRHPAOV data includes B300 as part of the declared performance set (again, confirm against the current datasheet/DoP for the exact product and configuration being submitted).
The biggest approvals trap: “1m² free area” vs aerodynamic free area (Aa)
The single most common trigger for back‑and‑forth is a requirement written as “1.0m² free area” without stating which definition of area is intended.
Surespan datasheets commonly present both:
- Geometric area / free area (often aligned with Approved Document B style reporting), and
- Aerodynamic area (Aa) to EN 12101-2, which is performance-based.
They can be materially different, and wind deflectors are frequently part of the aerodynamic performance configuration. Some datasheets explicitly show aerodynamic area (with wind deflectors) and geometric/free area (without wind deflectors).
Reality check: examples from Surespan datasheets
Example product |
Size |
Geometric / free area (typical ADB-style reporting) |
Aerodynamic area (Aa) to EN 12101-2 |
What this means in practice |
|---|---|---|---|---|
SRHP/AOV (Smoke Vent with Access) |
1050 × 1050 |
1.03 m² |
0.69 – 0.73 m² (check the exact datasheet / test version used for your submittal) |
If your strategy requires aerodynamic area, a “1m² free area” statement is not enough. |
SRHP/AOV (Smoke Vent with Access) |
1260 × 1260 |
1.52 m² |
1.05 m² |
Area performance improves with size, but still needs to be read as the correct area definition. |
SDP‑MD‑50 (Polycarbonate Dome AOV) |
1050 × 1050 |
1.01 m² (free area example) |
0.67 m² (aerodynamic area example, with wind deflectors) |
It is common for aerodynamic area to be lower than geometric/free area. |
Bespoke Smoke Vent (SRHE‑AOV / SRH‑AOV) |
1050 × 1050 |
1.03 m² |
0.73 m² (with wind deflectors) |
Where aerodynamic area is being scheduled, deflectors/configuration become part of compliance. |
Key takeaway: If you schedule aerodynamic area (Aa), treat the aerodynamic configuration as fixed. Removing wind deflectors late, restricting opening geometry, or changing the installed arrangement can invalidate the performance assumption and trigger approval comments.
If you want a deeper explanation with examples, see: Understanding geometric area vs aerodynamic area in smoke vents.
Specifier checklist: what to include to make your enquiry quote-ready
If you want fewer follow‑up questions, copy/paste this into your enquiry or specification schedule.
Schedule field |
What to state |
Why it matters |
|---|---|---|
Area requirement |
Required area in m² and whether it is geometric/free area or aerodynamic area (Aa) to EN 12101-2. |
Prevents the “1m² free area” misinterpretation. |
Performance classes |
RE ___ / SL ___ / WL ___ / T(___) / B ___ |
Stops “compliant?” becoming a multi‑email interrogation. |
Use case |
Smoke-only or dual-purpose (daily/comfort ventilation). If dual-purpose, request comfort cycle evidence. |
Avoids reliability disputes late in the project. |
Wind deflectors |
Allowed / required / not permitted (and why). |
Direct impact on aerodynamic performance and coordination (clashes, handrails, parapets). |
Roof exposure basis |
Snow and wind basis from structural engineer (typically kN/m²) plus roof pitch. |
Lets SL/WL be selected logically and defensibly. |
Opening & build-up constraints |
Structural opening size, upstand/kerb height constraints, roof build-up and any opening restrictions. |
Prevents performance being “designed out” by roof build-up constraints. |
Controls scope |
Fire alarm interface requirements, local switches, and any BMS integration expectations. |
Avoids confusion between ventilator performance and system/control requirements. |
For drawings, datasheets, wiring diagrams and fitting details in one place, use: Smoke Vent Resources.
Which smoke vent type should you link your schedule to?
Different projects start from different constraints (access, daylight, size, roof pitch). These links help you move from “EN12101-2 compliant?” to an evidence-backed product selection:
- Smoke Vent with Access (SRHP‑AOV) – roof access + smoke ventilation.
- Bespoke Smoke Vent (SRHE‑AOV) – larger or unusual structural openings.
- Glazed Smoke Vent (SRHG‑AOV) – daylight plus smoke ventilation.
- Dome Smoke Vent (SDP‑AOV) – polycarbonate dome options and standard set sizes.
- Exi‑Vent Roof Hatch – combined staircase access hatch + smoke ventilation functions.
Full range overview: AOV Smoke Vents (category)
Recommended next step (fastest route to approvals)
CTA: Request an EN 12101-2 evidence pack and a performance schedule template aligned to your project’s required RE/SL/WL/T/B classes and area definition (geometric vs aerodynamic).
Contact Surespan and include the checklist above. It will materially reduce follow‑up questions and speed up technical sign‑off.
FAQs
What does RE 1000 mean on a smoke vent?
RE is the reliability classification used in BS EN 12101-2. RE 1000 refers to the ventilator’s reliability performance for its fire function. If the unit is also intended for daily/comfort ventilation, ask for the separate comfort cycling declaration (often referenced as 10,000 cycles), as it is distinct from RE fire reliability.
What do SL and WL mean, and how do I choose the right class?
SL is the snow load class and WL is the wind load class. The practical way to choose them is to ask the structural engineer for the roof zone load basis (typically expressed in kN/m²) and schedule minimum SL/WL accordingly.
What does T(-15) mean?
T is the low ambient temperature class. It should be selected based on the project’s climate and roof exposure. If you have an external roof installation, include the required T class in the schedule rather than leaving it implicit.
What does B300 mean?
B is the resistance-to-heat classification. If your fire strategy expects a specific B class, include it in the schedule and request matching evidence for the ventilator configuration being installed.
Why do I see both geometric/free area and aerodynamic area on datasheets?
Because they represent different ways of expressing performance. “Free area”/geometric values are commonly used in UK guidance contexts, while aerodynamic area (Aa) is performance-based under EN 12101-2. Always specify which one your smoke ventilation strategy is using.
Do wind deflectors matter for compliance?
They can. Datasheets may present aerodynamic area values specifically with wind deflectors. If your schedule is based on aerodynamic area (Aa), treat deflectors and opening geometry as part of the tested performance configuration, not as optional extras that can be removed later without impact.
