Short answer: DW/144 is BESA's (the Building Engineering Services Association's) specification for the design, manufacture and installation of sheet metal ductwork, covering rectangular, circular and flat oval duct construction, hangers and supports, air leakage limits and testing — currently in its 3rd edition (2016), with an April 2024 addendum that aligns it with the revised TR19® Air specification for internal cleanliness (BESA Publications). It is a construction and installation specification, not a fire-rating certification.
What DW/144 actually covers
Per BESA's own published scope, the specification runs to eight parts: general scope, technical information the designer must provide, and detailed requirements for rectangular ducts, circular ducts, flat oval ducts, hangers and supports, ductwork-related information, and appendices (BESA Publications). In practical terms, that means it sets out approved materials, gauges and finishes for different duct types and sizes; air leakage limits and performance classes for low, medium and high pressure/velocity systems; construction standards for joints, seams and reinforcement; hanger and support spacing appropriate to duct size and pressure class; how smoke and fire dampers are fitted into ductwork as accessories; and testing methods and acceptance criteria for installed ductwork.
What DW/144 does not cover
This is the single most common point of confusion, and it's worth being precise about it: DW/144 covers how a fire or smoke damper is fitted into ductwork as a component, but it does not establish or test the fire-resistance rating of a complete fire-rated ductwork system. Fire performance is established through separate fire testing regimes, and a fire-rated duct system has to be installed exactly as tested by its manufacturer — DW/144 compliance elsewhere in the system doesn't substitute for that.
Similarly, internal cleanliness and hygiene management sits under a related but distinct specification (TR19 Air), which is why BESA's own April 2024 addendum to DW/144 specifically cross-references the revised TR19 Air document rather than folding cleanliness requirements directly into DW/144 itself (BESA Publications). If a specification or a subcontractor's marketing implies "DW/144 ductwork" is automatically fire-rated, that's a claim worth querying before it goes further.
Practical checklist
When DW/144 is referenced in your project specification, check which pressure class and leakage class apply to each ductwork section; whether any sections also carry a separate fire-rating requirement, and which manufacturer's tested system applies to those sections specifically; whether TR19 Air (or another cleanliness specification) also applies, and whether that's been called out separately from the DW/144 reference; and that pressure-testing evidence is actually being recorded, not just assumed because DW/144 is named in the spec.
Common mistakes
Assuming "DW/144 ductwork" means fire-rated ductwork — the two are separate, and conflating them is a genuine specification risk, not just semantics. Vague specification wording — "ductwork to DW/144" with no stated pressure class, leakage class or fire requirement — leaves room for ambiguity that surfaces at installation, not before. No pressure-testing records, despite DW/144 being referenced as the applicable construction standard. Overlooking the TR19 Air cross-reference introduced in the 2024 addendum, particularly on healthcare, laboratory or other cleanliness-sensitive projects.
What Cliventa needs
To install ductwork in line with DW/144 and your project specification, Cliventa needs the drawings and ventilation schedule (including pressure and leakage classes where specified), the full specification including any fire-rated ductwork requirements and the relevant manufacturer's system details, and confirmation of what pressure-testing evidence your project requires.
See our ductwork installation page, or our note on what should be included in a ductwork quotation.